NUNAVUT

NUNAVUT AIR BRAKE MANUAL

NUNAVUT AIR BRAKE MANUAL

Canadian Cataloguing in Publication Data Main entry under title: British Columbia air brake manual

ISBN 0-7718-8387-0

1. Air-brakes - Handbooks, manuals, etc. I. British Columbia. Motor Vehicle Branch II. Title: Air brake manual. 2. Reproduction of part or parts of this publication may only be made with the written consent of the Superintendent of Motor Vehicles, British Columbia.

TL269.B75 1983 629.2´46 C83-092274-1

MV 1852 (Rev. 05:91) DLD NUNAVUT AIR BRAKE MANUAL

FOREWORD

The Nunavut Air Brake Manual has been prepared The illustrations of the various types of air brake to assist a driver in determining the basic functions of system designs and explanations are provided for air brake systems. The manual has been designed in a instructional purposes, and are not to be interpreted in manner that study questions are included in order any way so as to supersede the requirements of that a reader may self-test his/her understanding of the Motor Vehicle Act, the Public Highways Act and the subject matter. the regulations pursuant to these acts. The study of the content of this manual, together A professional driver knows that attitude is a major with practical instruction, is recommended to a driver factor in trouble-free driving. This driver also knows who is preparing him/herself for the Branch’s air brake that a knowledge of safety equipment installed in a examination. Drivers who have qualified and are vehicle, which is maintained on a scheduled basis, is authorized to operate the air brake-equipped vehicles another major factor. All drivers are encouraged to are encouraged to review the manual on a periodic drive professionally at all times, thereby contributing basis to ensure they are fully aware of problems that to efforts to reduce accidents on our highways. can occur, resulting from air brake system defects.

Director Motor Vehicles Division NUNAVUT AIR BRAKE MANUAL

CONTENTS

SECTION I Hand Operated Valve ...... 31 Two-Way Check Valve ...... 31 BRAKES AND BRAKING Tractor Protection ...... 33 Heat, Energy, Traction, Friction ...... 6 Automatic Trailer Supply Valve System ...... 33 Speed, Weight, Distance ...... 6 Tractor Supply Valve ...... 34 How We Obtain Force...... 7 Tractor Protection Valve ...... 34 Stopping Distance ...... 8 Tractor and Trailer Unit Coupled ...... 36 Section Summary Questions ...... 8 Charging the Trailer System ...... 36 Brake Application – Foot Valve ...... 37 Brake Application – Hand Valve...... 37 SECTION II Emergency Applications...... 38 Service Line Rupture...... 38 THE COMPONENTS OF AN AIR BRAKE SYSTEM Supply Line Rupture...... 39 Compressor...... 12 Loss of Main Reservoir Air ...... 39 Reservoirs ...... 13 Manually Operated Trailer Supply Valves ...... 40 Foot Valve ...... 14 Section Summary Questions ...... 41 Brake Chambers and Slack Adjusters ...... 14 Wedge Type Brake ...... 16 Disc Brakes ...... 16 SECTION V Section Summary Questions ...... 17 DUAL AIR SYSTEMS

A Simple Dual Circuit Air System ...... 44 SECTION III Combination Truck and Trailer ...... 46

T-75 Off-Highway System, Single Unit ...... 47 HOW THE BASIC SYSTEM WORKS L-75 Off-Highway System, Combination Simple Air Brake System ...... 20 with Schedule X Trailer ...... 48 One-Way Check Valve ...... 20 Schedule SX, Off-Highway Trailer Gauges ...... 21 with Spring Brake ...... 48 Brake Application Gauge ...... 21 Section Summary Questions ...... 49 Low Pressure Warning ...... 21 Wig-Wags ...... 21 Stop Light Switch ...... 21 SECTION VI Quick Release Valve ...... 21 PRE-TRIP INSPECTION Relay Valve ...... 22 Front Wheel Limiting Valve...... 22 Single Unit ...... 52 Tandem Rear Axles ...... 23 Combination Unit ...... 52 Parking Brakes ...... 24 Brake Adjustment ...... 53 Dual Control Valve and Reservoir System ...... 26 Air Operated Disc Brakes...... 53 Mechanical Release ...... 26 In Service Check ...... 53 Air Activated Hydraulic Brakes ...... 27 Maintenance and Servicing of the Air Brakes...... 54 Section Summary Questions ...... 28 Section Summary Questions ...... 54 Metric Conversion Table ...... 54

SECTION IV

TRAILER SYSTEMS

Glad Hands...... 30 Application Line ...... 30 NUNAVUT AIR BRAKE MANUAL

SECTION I NUNAVUT AIR BRAKE MANUAL

SECTION I BRAKES AND BRAKING HEAT, ENERGY, TRACTION, FRICTION

SPEED, WEIGHT, DISTANCE HOW WE OBTAIN FORCE STOPPING DISTANCE SECTION SUMMARY QUESTIONS

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NUNAVUT AIR BRAKE MANUAL SECTION I

1 To stop the vehicle in /10 of the time it took to accelerate BRAKES AND would require a stopping force of ten times the accelera- tion force – the equivalent of approximately 2,000 horse- BRAKING power. If the vehicle had six wheels, each wheel would 1 have to provide /6 of the braking force. If one or two of the wheels had brakes that were not properly adjusted, the

other wheels would have to do more than their share of the braking, and that might be more than their brakes were constructed to stand. Excessive use of the brakes HEAT-ENERGY- would then result in a buildup of heat greater than the brake drums could absorb and dissipate. Too much heat would result in brake damage and possible failure. TRACTION-FRICTION For a vehicle to move along the highway, an internal combustion engine must convert its HEAT ENERGY into mechanical ENERGY. This mechanical ENERGY goes from the engine to the driving wheel tires by means of a system of connecting rods, shafts and gears. The final factor that moves the vehicle is the amount of TRACTION its tires have on the road surface. TRAC- TION is the ability of a tire to grip the road surface on which it rolls. The vehicle’s acceleration rate depends on the power the engine develops and the amount of TRACTION the tires have on the road surface. FRICTION is the force which resists movement between two surfaces in contact with each other. To stop a vehi- cle, the brake shoe linings are forced against the 250° C 425° C 1100° C machined surfaces of the brake drums, creating FRIC- NORMAL MAXIMUM PANIC! TION. This FRICTION produces HEAT. The engine converts the ENERGY of HEAT into the ENERGY of motion; the brakes must convert this ENERGY of motion back into the ENERGY of HEAT. The FRICTION between brake drums and linings gener- Most brake linings operate best at around 250° C and ates HEAT while reducing the mechanical energy of the should not exceed 425° C. It’s important to understand revolving brake drums and wheels. The heat produced that the power needed to stop generates heat which is absorbed by the metal brake drums, which dissipate could ruin the brakes. the heat by passing it off into the atmosphere. The amount of heat the brake drums can absorb depends on the thickness of the metal of which they are made. When enough FRICTION is created between the brake linings and the drums, the wheels stop turning; but the final SPEED-WEIGHT- factor that stops the vehicle is not the brakes, but the TRACTION between the tires and the road surface. DISTANCE If an engine of 200 horsepower accelerates a vehicle to The distance required to stop a vehicle depends on its 100 km/h in one minute, imagine the power needed to speed and weight, in addition to the factors of energy, stop this same vehicle. Not only that, but the vehicle might heat and friction. The brake force required to stop a have to be stopped in an emergency, in as little as six vehicle varies directly with its weight and the “square” 1 seconds (just /10 of the time it took to reach 100 km/h). of its speed. For example, if the weight is doubled, the stopping force must be doubled to be able to stop in the same distance. If the speed is doubled, the stopping force must be increased four times to be able to stop in the same distance. And, when weight and speed are both doubled, the stopping force must be increased eight times to be able to stop in the same distance. For example, a vehicle carrying a load of 14000 kgs force at 16 km/h is brought to a stop in a distance of 30 metres by normal application of the brakes. If this same vehicle carried 28000 kgs at 32 km/h, it would require eight times the braking force to stop the vehicle in 30 meters. This would be more braking force than the brakes could provide. No vehicle has enough braking force when it exceeds its limitations.

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SECTION I NUNAVUT AIR BRAKE MANUAL

HOW WE OBTAIN FORCE B. USE OF AIR Force can also be multiplied by the use of air to gain a fur- ther mechanical advantage. Everyone has felt the force of air on a windy day. Air can be compressed (squeezed) into A. MECHANICALLY a much smaller space than that amount of air normally would occupy. For instance, air is compressed in tires to support the weight of a vehicle. The smaller the space into which air is squeezed, the greater the air ’s resistance will be to being squeezed. This resistance creates pressure, which is used to gain mechanical advantage. If a constant supply of compressed air were directed through a pipe that was one inch square, and if a one inch square plug were placed in the pipe, the com-

pressed air would push against the plug. Holding a scale Braking systems use devices to gain a mechanical advan- against the plug would register how many pounds of tage. The most common device for this purpose is lever- force were being exerted by the air against the plug. age. Look at this simple lever system:

If the scale registered ten pounds, for example, then it could be said the force was ten pounds on the one square inch surface of the plug. This would be ten pounds per square inch (P.S.I.).

The more the air in the supply tank has been com- A lever is placed on a pivot called the fulcrum. As the pressed, the greater the force that would be exerted on distance from A to C is four feet, and from C to B is one the face of the plug. foot, the ratio is four to one (4:1) Force has been multi- plied by the leverage principle. If a 100 lb. downward force is applied at point A, then the upward force at C. LEVERAGE & AIR PRESSURE point B is 400 lbs. In actual operation, pipes are round and plugs are diaphragms of flexible material acting against push rods. This is the result of the mechanical advantage of leverage. If compressed air of 120 P.S.I. acts on a diaphragm of 30 square inches, 3,600 lbs., of force is produced (120 x 30). Apply this force to a push rod to move a 6-inch slack adjuster operating a cam and the total force equals 21,600 inch pounds torque (3,600 x 6), or 1,800 foot pounds torque (21,600 ÷ 12). It requires 25 - 30 foot pounds of torque to tighten the wheel on a car. This com- parison illustrates the force obtained from using mechanical leverage and air pressure combined.

Compare the Points A, C, B to the previous lever diagram. 7

NUNAVUT AIR BRAKE MANUAL SECTION I

STOPPING DISTANCE SECTION SUMMARY In addition to the above factors, a driver must under- 1. What is the final factor that will determine if the stand what is meant by the term “stopping distance”. vehicle will move? Stopping distance consists of three factors: 2. What is the final factor that will determine if the vehicle will stop? Driver’s reaction time + Brake lag + Braking distance. 3. How is the heat dissipated that is generated by the REACTION TIME: The time it takes from the moment a brakes? hazard is recognized to the time the brake is applied, 4. If one set of brake shoes are poorly adjusted, what 3 approximately /4 of a second. (Reaction time is often effect could it have on the remaining sets of brake called “thinking time”). shoes in the system? BRAKE LAG: The time the air takes to travel through a 5. What is meant by the term “FRICTION”? properly maintained air brake system, (approximately 6. If the weight of the vehicle is doubled, how many 4 /10 of a second). times must the stopping power be increased? 7. If both weight of the vehicle is doubled, how many BRAKING DISTANCE: The actual distance the vehicle times must the stopping power be increased to be travels after the brake is applied until the vehicle stops. able to stop in the same distance? (The distance depends on the ability of the lining to pro- 8. If the speed of the vehicle is doubled, how many duce friction, the brake drums to dissipate heat and the times must the stopping power be increased to be tires to grip the road.) able to stop in the same distance? The professional driver never takes the brakes for grant- 9. What is compressed air? ed. The braking system must be tested and the adjust- 10. What does the abbreviation “P.S.I.” stand for? ment checked before placing the vehicle into service. The 11. If 40 P.S.I. is exerted against a diaphragm of professional understands the braking system, realizes 30 square inches in area, what is the total pounds the capabilities and limitations, and learns to use them to of force that could be exerted? 4 the best advantage. 12. “Brake lag” is approximately /10 of a second in a Heavy vehicles require powerful braking systems that well-maintained, single circuit brake system. What are obtained by use of mechanical leverage and air pressure. is meant by “brake lag”? Brakes must be used keeping in mind the heat generated 13. What is meant by the following terms? by friction. If the heat becomes too great, braking effec- “Reaction distance” – “Braking distance” – tiveness will be lost. The heavier the load and the faster “Stopping distance”. the speed, the greater the power needed to stop. Stopping distance is also affected by the driver ’s reaction time, brake lag, and braking distance. The professional driver is well aware that the vehicle, even NOTES with properly adjusted brakes, will not stop as quickly as a passenger vehicle.

COMPARATIVE STOPPING DISTANCES

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SECTION I NUNAVUT AIR BRAKE MANUAL

Section I of this manual has explained that it is possible to gain a mechanical advantage through the use of levers and that air under pressure can be used to gain a mechanical advantage. Section II will explain how air under pressure can be used to operate the air brakes of a vehicle. Piping diagrams have been kept simple in order to be easily understood. The piping arrangements found on vehicles in actual use on the highway might differ somewhat from the illustrations in this manual.

The diagrams in this manual ARE NOT to be interpreted as regulations for, or specifications of, air brake systems. 9

NUNAVUT AIR BRAKE MANUAL

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SECTION II NUNAVUT AIR BRAKE MANUAL

SECTION II THE COMPONENTS OF AN AIR BRAKE SYSTEM COMPRESSOR RESERVOIRS FOOT VALVE BRAKE CHAMBERS AND SLACK ADJUSTERS WEDGE TYPE BRAKES DISC BRAKES SECTION SUMMARY QUESTIONS

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NUNAVUT AIR BRAKE MANUAL SECTION II

COMPRESSION STROKE: The upward travel of the pis- THE COMPONENTS ton compresses the air in the cylinder. The rising pressure cannot escape past the inlet valve (which the compressed OF AN AIR BRAKE air has closed) and as the piston nears the top of the stroke, the pressurized air is forced past the discharge valve and into the discharge line leading to the reservoir. SYSTEM A basic air brake system capable of stopping a vehicle has five main components: 1. A COMPRESSOR, to pump air 2. A RESERVOIR or TANK, to store the compressed air 3. A FOOT VALVE, to regulate the flow of compressed air from the reservoir when it is needed for braking 4. BRAKE CHAMBERS and SLACK ADJUSTERS, the means of transferring the force exerted by the com- pressed air to mechanical linkages 5. BRAKE LININGS and DRUMS or ROTORS, to cre- ate the friction required to stop the wheels. It is necessary to understand how each of these compo- nents works before studying their functions in the air brake system.

THE COMPRESSOR Compressed air is the means of transmitting force to an air brake system. The source of the compressed air is the compressor. A compressor is designed to pump air. Air pumped into a tank will result in pressurizing the air, as UNLOADING: When sufficient pressure has been built was explained previously in this manual. up, the compressor goes into an “unloading” stage. The unloader plunger holds the inlet valves off their seats A piston type compressor operates on a similar principle until pressure drops to the pre-set cut in pressure which to that of the intake and compression strokes of an is regulated by the governor. engine. INTAKE STROKE: The downward stroke of the piston creates a lower pressure within the cylinder than the atmospheric pressure outside the compressor. This causes air to flow past the inlet valve (which the atmos- pheric pressure has opened)into the cylinder.

The compressor is driven by the vehicle’s engine, by either belts and pulleys or shafts and gears. In vehicles which the compressor is driven by belts, the belts should be checked regularly for cracks and tension. Belt adjust- ment is usually checked by pressing with a finger mid- way between the pulleys. A greater distance between the pulleys will affect the amount of permissible slack. If the 12

SECTION II NUNAVUT AIR BRAKE MANUAL

belts become too slack, they could slip, and the com- pressor will not achieve its maximum efficiency. While THE RESERVOIRS checking the drive belts also check the compressor for Reservoirs or tanks hold a supply of compressed air. A broken mounting brackets or loose mounting bolts. safety valve protects them from being over pressurized and bursting. The safety valve protects the air brake sys- The compressor is in constant drive with the engine. tem from an excessive buildup of air pressure. The valve Whenever the engine is running, so is the compressor. It consists of a spring loaded ball which will allow air to is usually lubricated from the engine lubrication system. exhaust the reservoir pressure into the atmosphere. The Some compressors are self-lubricating and require regu- valve’s pressure setting is determined by the force of the lar checks of lubricant levels. spring. A safety valve is normally set at 150 P.S.I. If the There are periods of time when it is not necessary for pressure in the system rises to approximately 150 P.S.I., the compressor to pump air. A common pressure in the pressure would force the ball off its seat, allowing the an air brake system is from a low of 85 P.S.I. to a high of pressure to exhaust through the exhaust port in the 105 P.S.I. Some systems operate between 105 P.S.I. and spring cage. When reservoir pressure is sufficiently 125 P.S.I. Minimum pressure is approximately 20 P.S.I. reduced (to approximately 135 P.S.I.), the spring will below maximum pressure. force the ball back onto its seat, sealing off the reservoir When the pressure has reached the system’s maximum, pressure. Not all safety valves have a manual release fea- the compressor goes into an “unloading” stage. ture as shown in the diagram below. Most compressors have two cylinders. In the unloading If the safety valve has to relieve the pressure, it indicates stage, the inlet valves are held open, allowing the air to that the governor or compressor requires service or be pumped back and forth between the two cylinders, repair. This should be done by a qualified mechanic.

instead of compressing it. During the “unloaded” stage , the compressor is able to cool. It is most important that the air in the air brake system be kept as clean as possible. Dirt in the system can cause trouble. The air from the atmosphere that enters the compressor must first pass through a filter to remove any dust parti- cles from the air. The air filter must be cleaned regularly. A dirty filter will restrict the flow of air into the com- IMPORTANT! SAFETY VALVE ADJUSTMENTS MUST pressor, reducing its efficiency. Some vehicles have the NOT BE TAMPERED WITH. ONLY QUALIFIED inlet port of the compressor connected to the air cleaner MECHANICS SHOULD SERVICE SAFETY VALVES. of the vehicle’s engine.

A governor controls the minimum and maximum air pressure in the system. As the compressor is in constant drive with the engine, the governor ’s job is to “unload” Reservoirs or tanks are also equipped with drain cocks the compressor when the desired pressure is reached. to drain off any moisture. When air is compressed, it The governor does this by directing air pressure to the becomes heated. The heated air cools in the reservoir, inlet valves of the compressor, holding them open when forming condensation. Oil leaking past the piston rings pressure in the system reaches its maximum. When the of the compressor mixes with this moisture to form pressure in the system drops by approximately 20 P.S.I., a sludge in the bottom of the reservoir. If allowed to the governor allows the inlet valves to close, returning accumulate, this sludge (water and oil) would enter the the compressor to its pumping stage. braking system. An excess of water in the system causes trouble with valves and other parts. In winter, water in the system may freeze, causing malfunction of valves or brake chambers.

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NUNAVUT AIR BRAKE MANUAL SECTION II

To minimize the amount of water collection, all tanks must be drained daily. Under extreme conditions, tanks THE BRAKE CHAMBERS may have to be drained more than once a day. Park the vehicle on a level surface, set the parking brake, block AND SLACK ADJUSTERS the vehicle’s wheels, open drain cocks fully. Allow all air pressure to escape, which will then permit the moisture, collected in the tank, to drain. Some tanks have more than one compartment and each compartment has its own drain cock. Briefly opening the valve just to allow some of the air to escape DOES NOT drain the moisture! Some reservoirs are equipped with automatic reservoir drain valves (spitter valves). These may be drained manually by pushing up on a rod on the underside of the valve. Most vehicles are equipped with more than one reser- voir. This gives the system a larger volume of main reser- voir air. As the first tank collects more of the moisture and oil from the compressor, it is called the “wet tank”. The second tank is usually further from the compressor and so collects drier or cleaner air. This tank is called the “dry tank”. A brake chamber is a circular container divided in the middle by a flexible diaphragm. Air pressure pushing against the diaphragm causes it to move away from the THE FOOT VALVE pressure, forcing the push rod outward against the slack The foot-operated valve is the means of applying air to adjuster. The force exerted by this motion depends on air operate the brakes. The amount of distance the treadle of pressure and diaphragm size. If a leak occurs in the foot valve is depressed by the driver determines the the diaphragm, air is allowed to escape, reducing the amount of air pressure that will be applied, but the effectiveness of the brake chamber. If the diaphragm is MAXIMUM APPLICATION WILL NOT EXCEED THE completely ruptured, brakes become ineffective.

PRESSURE IN THE RESERVOIR. Releasing the foot valve treadle releases the brakes.

Front brake chambers are usually smaller than rear brake chambers because the front axles carry less weight than the rear axles. A brake chamber is usually mounted on the axle, near the wheel that is to be equipped for braking. Air pressure is fed through an inlet port. The air pushes When the driver applies the brakes, depressing the trea- against the diaphragm and the push rod. The push rod is dle part way, the foot valve will automatically maintain connected by a clevis and pin to a crank arm type lever the application air pressure, without the driver having to called a “slack adjuster”. This converts the pushing adjust the pressure of his/her foot on the treadle. motion of the push rod from the brake chamber to a twist- Releasing the treadle allows the application air to be ing motion of the brake camshaft and “S” cams. When the exhausted through the exhaust ports to the atmosphere. air is exhausted, the spring in the brake chamber returns Air treadles are spring loaded, producing a different the diaphragm and push rod to the released position. “feel” from hydraulic brake application. 14

SECTION II NUNAVUT AIR BRAKE MANUAL

As indicated by its name, the slack adjuster is also the means of adjusting the “slack” or free play in the linkage between the push rod and the brake shoes. This slack occurs as the brake linings wear. If the slack adjusters are not adjusted within the limitations, effective braking is reduced and brake lag time is increased. If too much slack develops, the diaphragm will eventually “bottom” in the brake chamber. If this condition is allowed to occur, the brakes will not be effective at all.

Some systems have automatic slack adjusters which adjust automatically to compensate for brake lining wear, thus maintaining the correct clearance between the brake lining and drum. Automatic slack adjusters must be checked regularly to ensure that correct adjustment is being maintained.

NOTE: Detailed brake adjustment procedures are out- lined in Section VI. The diagram below illustrates a common type of brake assembly used on truck rear axles and trailer axles. A front axle assembly has the brake chamber and slack adjuster mounted on the backing-plate because of the steering action.

The diagram illustrates a common type of slack adjuster, showing the worm adjusting gear. When the brakes are fully applied, the angle between the push rod and the arm of the slack adjuster should be no less than 90 degrees (a right angle). On this type of slack adjuster, the adjusting worm bolt is turned until the brake linings 1 1 touch the drums and then backed off, normally /4 to /2 a turn. A locking device, which may be a spring loaded collar over the head of the adjusting bolt, must be depressed when the wrench is slipped over the bolt head. Some slack adjusters use a spring loaded internal check ball to lock the adjustment. The more often the dri- ver checks the “slack”, the less the probability of brake failure. Vehicles rarely “lose” their brakes because of loss of air; it is usually a loss of adjustment.

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NUNAVUT AIR BRAKE MANUAL SECTION II

Brake lining material is attached to the shoes. The material used depends on the braking requirements of the vehicle. Brake lining must give uniform output of brake effort with minimum fade at high temperature. Fading or a reduction in braking effort occurs when the heated drums expand away from the brake linings. The brake linings also lose their effectiveness with over- heating. The twisting action of the brake cam shaft and “S” cam forces the break shoes and linings against the drums. The brake linings generate heat from friction with the brake drum surface. The thickness of the drums determines the amount of heat they are able to absorb and dissipate to the atmosphere. Drums worn thin will build up heat too

quickly. Dangerously undependable brake performance will result from distorted drums, weak return springs, Spring brakes added to these units are of the piggy-back improper lining, poor adjustment, or grease or dirt on type. the lining. Drums must never be turned or worn beyond the manufacturer ’s specification.

DISC BRAKES

WEDGE TYPE BRAKES Here is another example of a type of brake assembly used on some air brake equipped vehicles. The action of the brake chamber push rod forces a wedge shaped push rod between the brake shoe rollers. This forces the brake shoe lining against the brake drum.

The air activated heavy truck disc brake is similar in principle to the disc brake used on passenger vehicles. Air pressure acts on a brake chamber and slack adjuster, activating the brakes. For light truck and passenger car braking systems, hydraulic pressure is used. Instead of The vehicle may be equipped with a single chamber or the cam or wedge used in conventional heavy truck two chambers on each wheel, depending on the vehicle’s drum brakes, a power screw is used. A “power screw” size and style. works like a C-clamp, so that the lining pads exert equal These brakes may be equipped with a self-adjusting force to both sides of the disc or rotor. Some types of disc mechanism or with a manual “star wheel” adjuster. The brakes have a built-in automatic adjuster. Disc brakes “star wheel” adjustment is made with the vehicle jacked that require manual adjustment have adjustment specifi- up, to ensure that the brake linings do not drag. Manual adjustment of wedge type brakes is usually a job for a cations different from conventional “S” cam braking mechanic. systems. ALWAYS CHECK MANUFACTURER’S SPECIFICATIONS BEFORE ADJUSTING. 16

SECTION II NUNAVUT AIR BRAKE MANUAL

SECTION SUMMARY 1. What are the five basic components of an air brake system? 2. What are two standard main reservoir pressures for the operation of a vehicle’s air brakes? 3 At what pressure should the governor cause the compressor to return to its pumping stage? 4. How is a plugged air filter likely to affect the air compressor? 5. What causes moisture to form in the air brake system? 6. When is the compressor able to accomplish most of its cooling? 7. How are most compressors lubricated? 8. How often should the reservoirs be drained? 9. Is it necessary to allow all the pressure to escape from the reservoir in order to remove the moisture and sludge which may have accumulated? 10. What is the maximum pressure available for a full brake application at any given time? 11. What will result if the brake drums are worn thin or turned too far? 12. If the governor valve failed to “unload” the compressor, what would be the result? 13. What is the purpose of having more than one reservoir? 14. What are two functions of the slack adjuster? 15. Does the amount of slack in the brake linkages have any effect on the braking efficiency of the vehicle? 16. What is the advantage of keeping the brake chamber push rod travel adjusted to minimum travel? 17. What is the most common cause of loss of effective braking in an air brake system, loss of air pressure or loss of brake adjustment? 18. Do automatic slack adjusters on “S” cam brakes require checking? 19. Can the adjustment on air operated disc brakes differ from “S” cam type brakes? 20. What occurs when drum brakes become overheated? 21. What causes brake fade at high temperatures? 22. What is the main function of the foot valve? 23. Why does the “feel” of an air operated foot valve differ from a hydraulic brake pedal? 24. On what principle does a disc brake operate?

NOTES

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NUNAVUT AIR BRAKE MANUAL

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SECTION III NUNAVUT AIR BRAKE MANUAL

SECTION III HOW THE BASIC SYSTEM WORKS SIMPLE AIR BRAKE SYSTEM ONE-WAY CHECK VALVE GAUGES BRAKE APPLICATION GAUGE

LOW PRESSURE WARNING WIG-WAGS STOP LIGHT SWITCH QUICK RELEASE VALVE RELAY VALVE FRONT WHEEL LIMITING VALVE TANDEM REAR AXLES PARKING BRAKES DUAL CONTROL VALVE AND RESERVOIR SYSTEM MECHANICAL RLEASE AIR ACTIVATED HYDRAULIC BRAKES SECTION SUMMARY QUESTIONS

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NUNAVUT AIR BRAKE MANUAL SECTION III

The first tank in the system collects most of the moisture, HOW THE BASIC and is referred to as the wet tank. The second tank is referred to as the dry tank. Reservoirs vary in size. The SYSTEM WORKS size of the tank or tanks installed on a vehicle depends on the number and size of brake chambers. To prevent air from flowing back from the reservoirs to A SIMPLE the compressor, a ONE-WAY CHECK VALVE (9) is installed. This valve allows the air to flow in one direc- AIR BRAKE SYSTEM tion only. The valve is spring loaded. Pressure at the inlet NOTE: ALL PIPING DIAGRAMS ARE USED TO ILLUS- side overcomes the spring pressure and lifts the check TRATE BACSIC BRAKING PRINCIPLES ONLY AND valve ball, or disc, off its seat. Air passes through the DO NOT ILLUSTRATE ACTUAL AIR BRAKE SYSTEMS. valve to the outlet. When pressure at the outlet becomes greater than at the inlet, together with the spring pres- sure, the check device seats, preventing air from flowing BASIC OPERATION PRINCIPLE back through the valve. Air is pumped by the compressor (1) to the reservoir (2), which is protected from over pressurization by a safety valve (3). The governor (5) controls the pressure in the reservoir by governing the compressor. Air is available from the reservoir to the bottom of the foot valve (6). The driver pushes down the foot valve treadle and air pres- sure flows to the front and rear brake chambers (7, 8). The brake chamber push rods move the slack adjusters. The slack adjusters rotate the “S” cams, forcing the brake shoes against the drums. This causes friction which stops the wheels. The driver releases the foot valve trea- dle, and the air in the brake chambers is allowed to exhaust through the foot valve, releasing the brakes. Other valves are necessary to ensure smooth and efficient operation.

ONE-WAY CHECK VALVE In the diagram below, two reservoirs are shown. This gives the system a larger volume of main reservoir air.

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SECTION III NUNAVUT AIR BRAKE MANUAL

GAUGES WIG-WAGS All vehicles are equipped with a pressure gauge (10) to There are two common types of “wig-wag” low pressure indicate the amount of air pressure in the main reservoir warning devices that may be used. Both types will drop system. This gauge is mounted in the cab, usually on the into the driver ’s view when the pressure in the system dashboard. Common operating pressures are 85 P.S.I. to drops below approximately 60 P.S.I. The automatic 105 P.S.I. and 105 P.S.I. to 125 P.S.I., depending on the warning device will rise out of the driver ’s view when system. Monitoring the gauge will alert the driver to any the pressure in the system rises above 60 P.S.I. The man- unusual changes in pressure. ual reset type must be placed in the “out of view” posi- tion manually and will not stay in place until the pres- sure in the system goes above 60 P.S.I.

Whichever warning system is used, buzzer, lights or wig-wag, the driver MUST STOP his/her vehicle and find BRAKE the cause of the air loss. The air pressure remaining in the system (approximately 60 P.S.I.) is enough for brake APPLICATION GAUGE application if the driver acts promptly. An additional gauge can be installed on the dash to indi- cate the application pressure when the brakes are applied. This gauge can be piped to indicate the pressure of either a foot application or of hand application. (Hand STOP LIGHT SWITCH application will be explained later in the manual.) Any driver following must be warned that speed is being reduced or the vehicle is being stopped. The STOP LIGHT SWITCH (12) is an air operated electric switch which turns on the brake lights on the rear of the vehicle when a brake application is being made.

QUICK RELEASE VALVE The application of the brakes in the simple system was described earlier. In such a basic system, when the driver releases the foot valve, it would be necessary for the air

LOW PRESSURE WARNING All vehicles equipped with air brakes must have a device to warn the driver if the air pressure in the system drops to a dangerous level.

Should the air pressure drop below approximately 60 P.S.I. due to overuse or leaks, the low pressure indicator switch (11) will turn on a red warning light on the dash, or cause a buzzer to sound. Some vehicles are equipped with both a light and a buzzer to warn the driver of a low air pressure condition.

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NUNAVUT AIR BRAKE MANUAL SECTION III

under pressure in the brake chambers to return back to The driver places the control valve in the “normal” the foot valve to release the brakes. This releasing action position for dry road surfaces and the front braking would be slowed in long wheel base vehicles, due to application pressure is normal. On a slippery road longer lines between the foot valve and the rear brake surface, the driver may flip the control valve to the “slip- chambers. To allow the brakes to release quickly and pery road” position. In this position, the control valve fully, by discharging the application air near the brake will cause the LIMITING VALVE to operate. Application chambers, a quick release valve (13) may be installed. air pressure to the front wheels is then reduced to 50 per- cent of the application air pressure being delivered to the rear brake chambers.

RELAY VALVE The foot valve is usually located closer to the front wheels than to the rear wheels. The longer the distance from the foot valve to the rear chambers, the more time it will take (known as brake lag) before the rear brakes apply. To correct this condition on a long wheel base vehicle, a RELAY VALVE (14) is installed near the rear brake chambers. A larger diameter pipe is connected between the main reservoir and the relay valve. The air line from the foot valve to relay valve now becomes a “control line”. (The air in the control line “dead ends” at the relay valve.) When the foot valve is depressed, the air pressure in the control line acts on the top section of the relay valve, causing the relay valve to “relay” reservoir air directly to the rear brake chambers through the larger diameter pipe. The pressure of the reservoir air delivered in this way will be the same as the control pressure delivered by the foot valve. Releasing the foot valve exhausts the control air to the relay valve, * DELIVERY PORTS NOT SHOWN allowing it to cut off the flow of reservoir air to the rear chambers, in turn exhausting the air in the brake chambers Some systems are equipped with an AUTOMATIC by the quick release feature of the relay valve. LIMITING VALVE. (17)

FRONT WHEEL This valve will hold off brake application to the front wheels from 0 to 10 P.S.I., depending on how it has been LIMITING VALVE preset. Between the preset pressure and 40 P.S.I. of brake For better steering control on a slippery road surface, it application, the reduction is approximately 50 percent. can be an advantage to reduce the braking effect to the Brake applications between 40 P.S.I. and 60 P.S.I. are front wheels. This can be accomplished by installing a reduced by less than 50 percent. Brake applications over control valve (15) in the cab, and a FRONT WHEEL 60 P.S.I. are not reduced, full application is directed to the LIMITING VALVE (16) on the front axle. front wheels. 22

SECTION III NUNAVUT AIR BRAKE MANUAL

CHECK YOUR UNDERSTANDING illustrates an air brake system of a vehicle equipped with an automatic front wheel limiting valve (17), a quick From the above diagram name each numbered compo- release valve (13) and a tandem set of rear axles. Both nent and briefly describe its function in the system. Write axles of the tandem set are equipped with brakes. your answers on a separate sheet of paper. A relay valve (14) is used to provide quicker application pressure to the tandem rear axles. TANDEM REAR AXLES The air brake system discussed previously is that of a vehicle equipped with a single rear axle. The diagram

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NUNAVUT AIR BRAKE MANUAL SECTION III

Application of the dash control valve exhausts air from PARKING BRAKES the spring brake chamber, causing spring force to activate the spring brake. (SPRING BRAKES) Spring type parking brakes may be installed on an air brake equipped vehicle to ensure a reliable parking brake system. In the service brake system, the brakes are held retracted by springs, and applied by air pressure. Spring type parking brakes are applied and remain applied WITHOUT AIR PRESSURE. The parking brake chambers are attached to the service brake chambers and operate the brakes through the same linkage. Therefore, the effectiveness of the parking brake depends on the service brake adjustment. A control valve (usually a square, yellow button) in the cab allows the driver to exhaust air out of the parking brake circuit to apply the brakes, or to repressure the circuit to release them. The system can also act as an emergency brake. Loss of air from the main system may automatically apply the brakes, depending on how the system is piped.

During normal driving, air pressure cages the spring, holding it ready for parking or emergency braking. PARKING BRAKE SYSTEMS

The installation of parking brakes and their piping arrangements into a vehicle air brake system will vary depending on the vehicle make. Control valves will vary, depending on the manufacturer and type of piping arrangements.

During normal service brake operation, the spring brake does not apply. Air pressure keeps the spring caged.

This type of spring loaded valve requires that the driver push the button to release the parking brakes. This valve cannot be left in the released position below approximately 35 P.S.I. pressure in the main reservoir system. Any time the main reservoir pressure drops to approximately 35 P.S.I., this valve will exhaust automatically, placing the parking brakes into full application. Similar types of spring loaded valves require that the driver pull the button out to release the parking brakes. There is a single type of push-pull control valve in use that does not have an automatic release feature. To apply the parking brakes, the valve must be operated manually, even though the main reservoir pressure has been emptied.

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SECTION III NUNAVUT AIR BRAKE MANUAL

USING THE SINGLE CONTROL PARKING BRAKES PARKING BRAKE SYSTEM The above diagram illustrates spring parking brakes (18) The diagram below illustrates the use of a third tank with added to the brake chambers of the rear axle on the a single control, used on the rear axle of a single unit. single unit vehicle. A control valve (19) is mounted in the A control valve (19) is mounted in the cab. A supply line cab. A supply line of reservoir air is piped from the dry of reservoir air is piped from the dry tank through a tank to the control valve. Opening the control valve one-way check valve (9) into a third tank. Closing the admits main reservoir air pressure to the parking brake control valve shuts off the supply of reservoir air units, releasing them. pressure and exhausts the existing pressure in the Closing the control valve shuts off the supply of parking brake units, allowing them to apply the brakes. reservoir air pressure and exhausts the existing pressure If the main reservoir air in the system should be in the parking brake units, thus applying the brakes emptied, the parking brakes will not apply, because the one-way check valve will isolate the pressure in the third tank. If the spring (parking) brakes are to be used to stop the vehicle, the driver will have to set the parking brakes manually with the cab control valve.

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NUNAVUT AIR BRAKE MANUAL SECTION III

The emergency release would only be used to move the DUAL CONTROL VALVE vehicle from an undesirable location, if the parking brakes had been applied due to allow main reservoir air AND condition. RESERVOIR SYSTEM CAUTION: Parking brakes should be in the released position before making a service brake application. A Some vehicles, such as buses, may also be equipped with full brake application, made when the parking brakes an EMERGENCY RELEASE TANK (2). are applied, can compound the force exerted on the slack In this system, if main reservoir pressure is lost, the adjusters and linkage which could result in damage or spring brakes will automatically apply. brake failure. Compounding is the combination of two If the parking brakes have applied because of a loss of forces; the force applied by the spring brakes and the main reservoir air, the driver can draw reserve air from force applied by the service brake. the emergency release tank to release the parking brakes. NOTE: Spring type brakes are primarily a parking A dual parking brake control (19) is used together with brake, but in the event of loss of main reservoir air, they the emergency release tank. The driver must press on the can assist in stopping the vehicle. How quickly they will emergency release button. Releasing the emergency stop the vehicle depends on such factors as: release button will automatically allow the parking The weight and speed of the vehicle; brakes to re-apply. The steepness of the grade; The spring force of the spring brakes which have been installed; and, The adjustment of the service brakes.

MECHANICAL RELEASE Some spring type parking brakes can be released mechanically by “winding them off” or “caging” them. A bolt, which runs through the centre of the chamber body, is turned to compress the spring. It may be neces- sary to first remove a lock plate and stud, to gain access to the head of the bolt. Other types have a plug which

26

SECTION III NUNAVUT AIR BRAKE MANUAL

must first be removed and a bolt inserted. In some cases, a special wrench is required. Instruction on how to AIR ACTIVATED “cage” is usually on the body of the parking brake. If all air is lost and the vehicle has to be towed, the parking HYDRAULIC BRAKES

brake can be released by winding them off. Always When the foot valve is depressed, air pressure flows block the wheels when caging the parking brake spring. into the primary (rear brake) and secondary (front Caging means the brakes are being released. brake) circuits. The air pressure in each circuit acts upon that circuit’s brake chamber which transmits force to the master cylinder. Each master cylinder in turn transmits hydraulic pressure to the wheel cylinders, actuating the front and rear axle service brakes. When the driver pushes the parking brake control valve to the released position, air pressure behind a diaphragm in the spring brake chamber compresses the spring and maintains the parking brake in a released position. When the parking brake is applied by pulling the parking brake hand valve out, air in the diaphragm chamber is released and the spring extends, applying the rear brakes. If the main reservoirs drop to approximately 35 P.S.I., the parking brake valve will exhaust automatically, placing the parking brakes into full emergency/ parking application.

WARNING! Parking brakes should never be disassembled without first compressing the spring with a wind-off bolt. These springs are under extreme pressure and could cause serious personal injury if disassembly is attempted by anyone not experienced in servicing these units. Disassembly is a job for a mechanic.

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NUNAVUT AIR BRAKE MANUAL SECTION III

SECTION SUMMARY 1. How can the driver tell how much air pressure there is in the main reservoirs? 2. What must the driver do when a low pressure warn- ing system activates? 3. What is the purpose of a quick release valve? 4. What is the purpose of a relay valve? 5. What is the purpose of using a larger diameter pipe between the main reservoir tank and the relay valve? 6. If the front axle limiting valve is in the “slippery road” position, and the foot valve is depressed to make a brake application of 30 P.S.I., how much pres- sure will be applied in the front brake chambers? 7. How is the reservoir protected from over pressurization? 8. What stops pressurized air from flowing back into the compressor from the dry tank? 9. At what pressure should the low pressure warning device activate? 10. How is “brake lag” to the rear wheels minimized? 11. When should a driver use the front wheel limiting valve? 12. What is meant by “compounding” the brakes? 13. Why are spring brakes a reliable type of parking brake? 14. How are parking brakes held in the released position? 15. What are the functions of the cab-mounted parking brake control valve? 16. Will parking brakes apply “automatically” in all braking systems? 17. What is the reason for releasing the parking brakes before making a full brake application test? 18. What is the purpose of an emergency release reser- voir tank in a parking brake system? 19. How can some types of parking brakes be released without the use of air pressure? 20. What is the danger of disassembling a parking brake unit?

NOTES

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SECTION IV NUNAVUT AIR BRAKE MANUAL

SECTION IV TRAILER SYSTEMS GLAD HANDS APPLICATION LINE HAND OPERATED VALVE TWO-WAY CHECK VALVE TRACTOR PROTECTION AUTOMATIC TRAILER SUPPLY VALVE SYSTEM TRAILER SUPPLY VALVE TRACTOR PROTECTION VALVE TRACTOR AND TRAILER UNIT COUPLED CHARGING THE TRAILER SYSTEM BRAKE APPLICATION – FOOT VALVE BRAKE APPLICATION – HAND VALVE EMERGENCY APPLICATIONS SERVICE LINE RUPTURE SUPPLY LINE RUPTURE LOSS OF MAIN RESERVOIR AIR MANUALLY OPERATED TRAILER SUPPLY VALVES SECTION SUMMARY QUESTIONS

29

NUNAVUT AIR BRAKE MANUAL SECTION IV

tractor. These couplers have a snap-lock position, and a TRAILER SYSTEMS rubber seal prevents air from escaping. Before connection is made, couplers should be clean and It can be assumed that the system illustrated up to this free of dirt and grit. When connecting the glad hands, point is the air brake system of a truck unit. If a trailer start with the two seals together and the couplers at a was coupled to this unit, the brakes of the trailer would 90 degree angle to each other. A quick snap downwards have to be operated from the tractor. will join and lock the couplers. Vehicles equipped with The following diagram shows the piping of a unit, “dead-end” couplers should have these protection plates similar to the tandem axles of the truck unit. The trailer in use whenever the vehicle is used without a trailer. has a single axle equipped with brake chambers. This will prevent water and dirt form entering the cou- pler and lines. A “TEE” has been installed in the application line between the foot valve and the truck axle system. A line If the unit is not equipped with dead-end couplers, the has been connected from this tee to the trailer by a set of glad hands of the service line can be locked to the glad couplers called “GLAD HANDS” (20). hand of the supply line to keep water and dirt from entering the unused lines. The cleaner the air supply is kept, the less chance of brake problems! GLAD HANDS Glad hands and lines should also be secured to prevent This term refers to the coupling device used to connect the line from bouncing off the vehicle. This could seri- the service and supply lines of the trailer to the truck or ously damage the couplers.

THE APPLICATION LINE The application line is referred to as a SERVICE LINE. In this simple system used for an example, the driver depresses the foot valve treadle, and application air will be delivered to the tractor brake chambers and to the trailer brake chambers. When the driver releases the foot valve treadle, the application air to the trailer brake chambers must return to the foot valve to be exhausted to the atmosphere. In this example system, there would be disadvantages: If the trailer broke away from the tractor, the trailer would have no brakes.

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SECTION IV NUNAVUT AIR BRAKE MANUAL

If the service line parted or ruptured, the trailer brakes HAND OPERATED VALVES could not be applied, and the application air would be lost from the tractor if a brake application were made. For trucks that are intended to pull trailers, the hand operated valve is added to the air brake system to oper- If the air in the main reservoirs were lost, there would be ate the trailer brakes. This valve allows the driver to no way to apply the brakes of the tractor or the trailer. apply the trailer brakes independently of the tractor. The The trailer brakes cannot be applied independently from amount of application air pressure delivered depends on the tractor, and there is no way to set the trailer brakes the amount the valve is opened by the driver. Some when coupling to the tractor. valves must be closed by the driver; others will close automatically from any open position. Valves may be of The application and release of the trailer brakes would a type that will remain in the full open position only, or be slower than those of the tractor. they may be equipped with a locking device that will These disadvantages are overcome by the addition of the hold them in the desired position. lines and valves discussed in the following pages. NOTE: The hand valve is NOT to be used for parking, as air may bleed off if the engine is stopped or the hand valve moves to the released position. HAND VALVE AND TWO- WAY CHECK VALVE To provide a brake application to the trailer unit only, a HAND VALVE (21) and a TWO-WAY CHECK VALVE (22) are piped into the system. The purpose of the hand valve is to allow the driver to control independently the amount of application air to be directed to the trailer brakes when a trailer brake application is being made. It also provides a method of applying the trailer brakes when coupling the trailer to the tractor. The purpose of a two-way check valve is to allow control of the trailer brake by use of the hand or foot valve. This valve will permit air to flow from the source which is supplying the higher application pressures.

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NUNAVUT AIR BRAKE MANUAL SECTION IV

A TWO-WAY CHECK VALVE This valve allows air to be directed to one delivery pipe from either of two sources. A two-way check valve allows the source applying the higher pressure to shift the shuttle so that the higher pressure will be directed to the delivery or “service line.” This valve is used between the foot operated valve and the hand operated valve, for the purpose of independently controlling the trailer brakes. The driver has applied the brakes by using the foot valve. Application air is directed to the brake chambers of the tractor AND to the trailer brakes through a two- way check valve (22). The shuttle has shifted to the low pressure side, closing off any air flow toward the hand valve side. The hand valve (21) is in the closed position and equal pressure is being applied to the brake cham- bers of the tractor and the brake chambers of the trailer.

In this diagram, with the foot valve released, and the hand brake chambers. The two-way check valve in this appli- valve (21) opened, application air is directed from the cation has shifted to the low pressure side, closing off hand valve through the two-way check valve (22), to the any air flow toward the foot valve side.

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SECTION IV NUNAVUT AIR BRAKE MANUAL

The amount of application pressure through the hand There are two types of trailer supply valves in use. The valve depends on the amount that the valve is opened by most common is a spring loaded valve that, after being the driver. (But it cannot exceed main reservoir pressure!) opened manually, is held open by air system pressure. Any time a trailer brake application is made by use of the This device is called an automatic trailer supply valve. hand valve, the driver may depress the foot valve treadle. Some tractors have a manual trailer supply valve. These If the foot valve application is of a higher pressure than may be a toggle type switch or a push/pull type. that of the hand valve, the two-way check valve will shift The tractor protection valves vary in outward appear- to the lower pressure side, allowing the higher pressure ance, depending on make and model, but all perform the to be directed to the tractor and trailer brakes. same function: protecting the tractor air supply. If, during a foot valve application, the driver makes a higher pressure hand valve application, the two-way check valve will allow the higher hand valve application to be directed to the trailer brakes. Regardless of whether the trailer brakes are applied independently by means of the hand valve, or together with the tractor brakes by the use of the foot valve, the AUTOMATIC TRAILER maximum application pressure can only be the same as, or slightly less than, MAIN RESERVOIR PRESSURE. SUPPLY VALVE SYSTEM The diagram below illustrates that the main reservoir air is piped from the main reservoir lines to the trailer supply valve (24). The tractor protection valve (23) is fed by two lines, one from the trailer supply valve (24) and TRACTOR PROTECTION one from the two-way check valve (22). Leading off from A tractor protection system is added to prevent total the tractor protection valve are two lines, each with a loss of air from the tractor if the trailer breaks away, or glad hand coupler. These two lines are referred to as the if the connecting air lines between tractor and trailer SERVICE LINE and the SUPPLY LINE. become separated or ruptured. The tractor protection In the diagram the upper line is the service line and the system consists of two valves added to the tractor lower line is the supply line. system: the TRACTOR PROTECTION VALVE (23), and the TRAILER SUPPLY VALVE (24). Other names for the To understand the function of the trailer supply valve trailer supply valve are “trailer parking control” and and the tractor protection valve in the system, it is “emergency valve.” important to understand how they operate.

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NUNAVUT AIR BRAKE MANUAL SECTION IV

the valve will shut automatically, by spring pressure, TRAILER opening the exhaust port. The driver can close the valve manually, to uncover the exhaust port. SUPPLY VALVE This valve (usually a red octagonal button) is mounted in the cab of the vehicle, easily accessible to the driver. The driver opens the valve by pushing or pulling the TRACTOR button, depending on the type used. PROTECTION VALVE

This is an example of a tractor protection valve, which is usually mounted on the cap or chassis of the tractor.

Opening the valve permits main reservoir pressure The diagram below illustrates a tractor unit equipped to flow through the valve. This pressure is piped to the with a trailer supply valve (24) and a tractor protection tractor protection valve and the supply line glad hand. valve (23). The trailer is not coupled and the tractor is The valve is spring loaded, and will be held in the open being operated as a single unit. The driver has not position when sufficient pressure is reached. If the opened the trailer supply valve (24) and the hand valve pressure drops to a range of between 45-20 P.S.I., (21) is closed.

34

SECTION IV NUNAVUT AIR BRAKE MANUAL

In the diagram above, the driver has made a brake appli- If the driver, by mistake, applied the hand valve (21), cation with the foot valve (6), and application air is being with the trailer disconnected, the application air directed delivered to the tractor brake chambers. The two-way to the tractor protection valve would also be dead- check valve (22) has shifted to the low pressure side, ended. Again, no air loss would occur, if the trailer allowing application air in the control line to reach the supply valve (24) is in the closed position. tractor protection valve (23). There is no air loss from the tractor through the discon- nected glad hands (20).

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NUNAVUT AIR BRAKE MANUAL SECTION IV

will occur automatically in the event of ruptured or TRACTOR AND parted air lines between tractor and trailer, or loss of air from the main reservoir system. The driver may operate TRAILER UNIT COUPLED the cab-mounted trailer supply valve (24) to cause an In the diagram above, the trailer has been coupled to the emergency application of the trailer brakes. tractor, and the service and supply lines of the units have 3. The relay emergency valve has a one-way check valve been coupled by using glad hands. which stops air in the reservoir from going back to the The trailer unit has a reservoir (2) installed. This tank source of the supply. will provide a volume of air near the trailer chambers for normal or emergency braking. The tank is equipped with a draincock. A RELAY EMERGENCY VALVE (25) is mounted on the CHARGING THE trailer reservoir. (this valve can also be mounted directly on the trailer frame near the brake chambers.) The relay TRAILER SYSTEM emergency valve serves three main functions in the In the previous diagram, the compressor has raised the system: main reservoir pressure to maximum.

1. The RELAY part of the valve relays air from the trailer In the next diagram, the driver has opened the trailer reservoir to the trailer brake chambers during a brake supply valve (24) to allow the main reservoir air pressure application. This part of the valve operates like the to be directed through the tractor protection valve (23) to relay valve previously discussed. It also provides a the trailer. The air pressure passes through the relay emer- quick release of the trailer brakes. gency valve (25) to the reservoir on the trailer. Pressure will build up in the trailer reservoir to the same pressure 2. The EMERGENCY part of the valve directs trailer as the main reservoirs on the tractor. This is known as reservoir pressure to the trailer brakes, causing an “charging” the trailer system. The trailer supply valve will emergency application (“dynamiting”). This action remain in the open position when the pressure has built up to between 20 and 45 P.S.I., depending on the make.

36

SECTION IV NUNAVUT AIR BRAKE MANUAL

In this system, the brakes of both units can be released BRAKE APPLICATION – quickly.

FOOT VALVE The diagram above illustrates the air flow action during a brake application being made with the foot valve (6). BRAKE APPLICATION – The application air has applied the tractor brakes and the trailer brakes together. As previously explained, the HAND VALVE two-way check valve (22) has shifted, and application air The driver can use the hand valve (21) to apply the trail- is being directed through the tractor protection valve er brakes. The air flow is illustrated in the next diagram. (23) to the service line. The tractor protection valve (23) and relay emergency This control pressure moves through the service line to valve (25) are operated by the application air, as was act on the relay emergency valve (25). This control pres- explained in the foot valve application. sure will cause the relay emergency valve to direct reser- Closing the hand valve will release the brakes by closing voir air from the trailer tank to the trailer brake cham- off application air. The air pressure in the chambers and bers (26). This will be of the same P.S.I. as the control lines will exhaust, also as explained in the previous foot pressure, which was the P.S.I. of the application air by valve application. the foot valve. In such a system, brake lag time has been minimized. Release of the foot valve treadle stops the flow of appli- cation air. The relay portions of the valves return to their CAUTION: TRAILER BRAKES MUST NOT BE USED original positions, stopping the flow of air pressure. The TO HOLD A PARKED VEHICLE THAT IS LEFT UNAT- exhausting ports of the valves exhaust the air pressure TENDED. LOSS OF PRESSURE WILL RESULT IN LOSS from the brake chambers, releasing the brakes. OF BRAKES! ALWAYS SET THE PARKING BRAKE.

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NUNAVUT AIR BRAKE MANUAL SECTION IV

EMERGENCY SERVICE LINE RUPTURE If the service line is ruptured or disconnected, no action APPLICATIONS will take place until a brake application is made. A TRAILER BREAKAWAY would result in a separation In this diagram, the service line has ruptured, and the of the service line and the supply line. The sudden loss driver has made a brake application with the foot valve (6). of air pressure in the supply line will trigger the relay emergency valve (25) which causes the trailer reservoir The application air is directed to the control line through (2) to dump its air directly to the trailer brake chambers the tractor protection valve (23). Rupture of the service (26). This places the trailer brakes into emergency line will result in the escape of air pressure, causing a application. loss of pressure in the tractor system. This pressure drop will cause the tractor protection system to close off, The loss of pressure in the supply line also causes exhausting the supply line to the trailer. This will cause the trailer supply valve (24) to automatically shift to the the trailer brakes to go into an emergency application. close position. The trailer brakes may be released by opening the trailer The tractor brakes are operable, without air loss, supply valve (24) to recharge the trailer system. A because the tractor protection system has isolated further application of the foot valve or hand valve the tractor. would again trigger an emergency application. The trailer brakes will remain applied until either NOTE: Depending on the type of tractor protection the pressure in the trailer reservoir and lines is drained system used, the air loss from the tractor will stop off, or the supply line is repaired and the system immediately, or it will blow down to between 45 and is recharged. 20 P.S.I. and then shut off.

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SECTION IV NUNAVUT AIR BRAKE MANUAL

SUPPLY LINE RUPTURE LOSS OF MAIN

A rupture of the supply line (or an uncoupling of the RESERVOIR AIR supply line glad hands) will result in a drop of pressure Rupture of the compressor discharge line would result in the supply line between the trailer supply valve (24) in loss of pressure from the wet tank. When the pressure and the relay emergency valve (25). This will trigger the in the wet tank (2) of the tractor unit falls below the emergency action of the relay emergency valve, placing warning level, due to a compressor failure or excessive the brakes into emergency application. As in the previ- leakage on the tractor, the warning devices (11) will start ous examples, the trailer supply valve (24) will shift to to operate. In the diagram, the one-one check valve (9) the closed position. has prevented the main reservoir air in the dry tank from The operation of the tractor brakes will not be escaping back to the wet tank and the ruptured line. affected, if the tractor protection system is in There is sufficient reservoir air pressure in the dry tank working condition. for a limited number of brake applications to stop the The relay emergency valve (25) must be the no bleed- vehicle before the parking brakes are activated. (This back type, so no air is lost from the trailer. will depend on how the parking brakes are piped.)

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NUNAVUT AIR BRAKE MANUAL SECTION IV

If this pressure is lowered to approximately 45 - 20 P.S.I. tractor, the driver must shift the trailer supply valve to the tractor protection system will close automatically, the EMERGENCY position. Otherwise the tractor air placing the trailer brakes into an emergency position. pressure will bleed down and hold at 45 - 20 P.S.I.

The tractor protection system described in this manual RUPTURED SERVICE LINE: is an example of a vehicle equipped with a type of cabmounted trailer supply valve (24) which will close auto- As in the example, no action will occur until a brake matically when the pressure in the supply line drips below application is made. Application of the brakes with a 45 - 20 P.S.I. The valve may also be closed manually. ruptured service line will result in a loss of pressure in the system. When the main reservoir pressure drops to between 45 - 20 P.S.I., the trailer brakes will dynamite.

MANUALLY OPERATED RUPTURED SUPPLY LINE: As in the example, the loss of supply pressure will cause TRAILER SUPPLY VALVES the trailer brakes to dynamite. To prevent air loss from Some vehicles are equipped with a different type of cab- the tractor, the driver must shift the cab-mounted trailer mounted trailer supply valve, which must be operated supply valve to EMERGENCY. Otherwise the tractor air manually by the drive. It has two positions: NORMAL pressure will bleed down and hold at 45 - 20 P.S.I. and EMERGENCY. If a slow loss of main reservoir air occurs, when the The tractor will be equipped with a tractor protection supply line pressure drops to between 45 - 20 P.S.I., the relay valve, and the trailer unit with a relay emergency valve, emergency valve will cause the trailer brakes to dynamite. as in the previous system. The functions of the trailer supply valve, tractor protec- MANUAL DYNAMITING OF TRAILER: tion valve, and the relay emergency valve will be similar Any time the driver shifts the cab-mounted trailer supply to those illustrated. An important difference is that the valve to the emergency position, and the trailer system is trailer supply valve must be shifted to the EMERGENCY charged, the trailer supply valve will exhaust the supply position manually. line, dynamiting the trailer brakes.

The trailer brakes will remain applied only as long as air CHARGING THE TRAILER SYSTEM: pressure remains within the trailer system. How long the The driver places the trailer supply valve in the air in the system will hold the brakes applied depends NORMAL position and main reservoir air will be on how airtight the system is. As a safety precaution, directed to the trailer reservoir. parked trailers should always be blocked to prevent a

possible runaway. TRAILER BREAKAWAY: To move a trailer that has been parked with the brakes in The loss of emergency air in the supply line will cause the an emergency application, it is necessary to charge the trailer brakes to dynamite. To prevent air loss from the system to release the trailer brakes. 40

SECTION IV NUNAVUT AIR BRAKE MANUAL

SECTION SUMMARY 1. What is the purpose of a two-way check valve? 2. Why should the glad hands be protected when not in use? 3. How can a driver control the trailer brakes independently? 4. What are three ways of testing the emergency application of the trailer brakes? 5. Should the hand valve of a tractor trailer unit be used for parking? 6. What is the main purpose of the tractor protection valve? 7. What is the main purpose of the trailer supply valve? 8. Name three functions of the relay emergency valve. 9. Describe the function of the supply line. 10. Describe the function of the service line. 11. What will occur if the supply line ruptures? 12. What will occur if the service line ruptures? 13. What will occur if a brake application is made with a ruptured service line? 14. If the foot valve and the hand valve are operated at the same time, can the application pressure be greater than the reservoir pressure?

NOTES

41

NUNAVUT AIR BRAKE MANUAL

42

SECTION V NUNAVUT AIR BRAKE MANUAL

SECTION V DUAL AIR SYSTEMS A SIMPLE DUAL CIRCUIT AIR SYSTEM

COMBINATION TRUCK AND TRAILER

T-75 OFF-HIGHWAY SYSTEM, SINGLE UNIT

L-75 OFF-HIGHWAY SYSTEM, COMBINATION WITH SCHEDULE X TRAILER SCHEDULE SX, OFF- HIGHWAY TRAILER WITH SPRING BRAKE

SECTION SUMMARY QUESTIONS

43

NUNAVUT AIR BRAKE MANUAL SECTION V

tions (two foot valves in one). One section of this dual foot DUAL AIR SYSTEMS valve controls the primary circuit and the other section controls the secondary circuit. When a brake application More and more heavy duty vehicles on the road today is made, air is drawn from the primary tank (green) are using a Dual Circuit Air System. The system has been through the foot valve and is passed on to the rear brake developed to shorten stopping distances and reduce chambers. At the same time, air is also drawn from the brake failures. At first glance, the dual system might secondary tank (red), passes through the foot valve and is seem complicated, but if you understand the basic air passed on to the front brake chambers. If there is an air system described so far, and if the dual system is sepa- loss in either circuit, the other circuit will continue to rated into its basic functions, it becomes quite simple. operate independently. Unless air is lost in both circuits, As its name suggests, the dual system is two systems the vehicle will continue to have braking ability. The or circuits in one. There are different ways of separating primary and secondary circuits are equipped with low the two parts of the system. On a two-axle vehicle, one pressure warning devices (11) and pressure gauges (10). circuit operates the rear axle and the other circuit operates the front axle. If one system has a failure, the DUAL CIRCUIT FOOT VALVE other system is isolated and will continue to operate.

A SIMPLE DUAL CIRCUIT AIR SYSTEM NOTE: ALL PIPING DIAGRAMS ARE USED TO ILLUS- TRATE BASIC DUAL CIRCUT PRINCIPLES ONLY AND ARE NOT TO BE INTERPRETED AS REGULATIONS FOR, OR SPECIFICATIONS OF, DUAL AIR BRAKE SYSTEMS. In the illustration below, air is pumped by the compressor (1) to the supply reservoir (2) which is protected from over pressurization by a safety valve (3). Pressurized air moves from the “wet” supply tank to the primary tank (green) and the secondary tank (red) through one-way check valves (9). At this point, the dual circuits start. Air from the primary tank is directed to the foot valve (6). Air is also directed from the secondary tank to the foot valve. The foot valve is similar to the one described earlier in the Single Circuit System, but has been divided into two sec-

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SECTION V NUNAVUT AIR BRAKE MANUAL

SIMPLE DUAL CIRCUIT SYSTEM air to maintain balance in the modulator valve, due to the WITH SPRING PARKING BRAKES primary circuit failure, the modulator valve then exhausts air pressure from the spring brake circuit. The When spring brakes are added to a dual circuit system amount of air released is equal to the amount of air the same type of dash control valve discussed previous- applied by the foot valve. The release of air in the spring ly is used. Blended air is used to supply the control valve brake circuit causes the drive axle to brake using spring (19). Blended air is air taken from the primary and brake pressure (18). When the brake is released, supply secondary circuits through a two way check valve (22). air from the secondary circuit (red) returns the spring With this piping arrangement the vehicle can have a fail- brakes to an off position. Brake applications can be ure in either circuit without the spring brakes applying repeated until all the air from the secondary circuit is lost, automatically. Unless air is lost in both circuits the spring but, as the air pressure drips below 85 P.S.I., the spring brakes will not apply. brakes won’t return to the full off position, in fact they will start to drag. At approximately 35 P.S.I., the spring SPRING BRAKES brake control valve (19) on the dash exhaust the remain- WITH MODULATOR VALVE ing air in the secondary circuit, and the spring brakes are fully applied. The only way the vehicle can be moved Spring type brakes in this system serve two purposes: first, after all air is lost is to repair the damaged circuit and as a parking brake, and second as an emergency system. If recharge the system, or cage the spring brake system. a failure occurs in the primary circuit (green), and a brake application is made, control air from the foot valve is Tandem tractors without steering axle brakes will have the directed to a spring brake modulator. As there is no supply primary and secondary systems split between the drive axles.

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NUNAVUT AIR BRAKE MANUAL SECTION V

spring brake valve to exhaust the air from the trailer spring COMBINATION TRUCK brake chambers applying the trailer brakes. The trailer brakes cannot be released under these conditions unless AND TRAILER WITH the lines are recoupled and the trailer tanks recharged. SPRING BRAKES If only the supply line breaks between tractor and trailer, the same sequence of events will occur. The trailer system is supplied by blended tractor air taken from the primary and secondary circuit through a A break or rupture in the service line will not affect two way check valve as previously described. the trailer until a brake application is made. A loss of pressure in the tractor system will then result, causing The system is charged by opening the trailer supply valve the same emergency brake application described above. (24), allowing air from the tractor to pass through the trac- However, the driver will be able to release the parking tor protection valve (23), and the trailer spring brake valve brakes by releasing the foot valve, rebuilding air (30) directly into the spring brake chambers (18). When air pressure and opening the trailer supply valve. enters, the pressure protection part of the trailer spring brake valve opens, allowing the air to fill the trailer tanks. To apply the parking brakes, the control valve (19) is closed, causing a loss of pressure in the line which When a brake application is made, blended control air applies the spring brakes as described above. acts on the relay valve (14) which releases air from the trailer tank to the brake chambers. The old and new tractor and trailer system are fully interchangeable, whether they are dual system or single If the tractor breaks away form the trailer, the service and circuit, and whether they are systems with spring brakes supply lines will be pulled apart. The sudden loss of air in or without. the supply line will cause the tractor protection valve to close, presenting air from escaping out of either broken connection. The air supply in the tractor is sealed off and is available to control the tractor brakes. At the same instant, NOTE: An air dryer (28) has been added to reduce the the sudden loss of air in the supply line cases the trailer amount of moisture in the system.

1. Compressor 17. Automatic Limiting Valve 2. Reservoir 18. Parking Brake (Spring) 3. Safety Valve 19. Parking Brake Control Valve 4. Drain Cock 20. Glad Hand Connector 5. Governor 21. Hand Valve 6. Foot Valve 22. Two Way Check Valve 7. Front Brake Chamber 23. Tractor Protection Valve 8. Rear Brake Chamber 24. Trailer Supply Valve 9. One Way Check Valve 26. Trailer Brake Chamber 10. Reservoir Pressure Gauge 27. Spring brake Modulator Valve 11. Low Pressure Indicator Switch 28. Air Dryer 12. Stop Light Switch 30. Spring Brake Valve 14. Relay Valve 46

SECTION V NUNAVUT AIR BRAKE MANUAL

Should a failure occur in the front axle circuit, the T-75 OFF HIGHWAY primary or secondary circuit will not be affected. SYSTEMS, SINGLE UNIT NOTE: A failure in any of the circuits will activate the low air warning system (11) and the driver MUST Air from the compressor is pumped into the supply tank stop the vehicle to determine the cause. Should the air in (blue). Pressurized air moves from the supply tank to the the supply system drop to approximately 35 P.S.I., the primary tank (green), the secondary tank (red) and the spring brakes will apply. front axle tank (brown) through one way check valves (9). When the air pressure reaches the governor cut-out In this diagram the vehicle is equipped with a variable setting (maximum 125 P.S.I.), the compressor cuts out and front wheel limiting valve (29). The application pressure is in its cooling or “unloaded” stage. When the air pres- delivered to the front axle is determined by the setting sure drops approximately 20 P.S.I., the governor (5) made by the driver. returns the compressor to its pumping or “loading” stage. To apply the spring parking brakes (18), the driver must When a brake application is made by pushing down the move the control valve (19) to the “park” position. this dual foot valve treadle (6), air from the front axle circuit exhausts the control pressure from the spring brake relay flows to the front axle relay valve and air from the valve (30) which then releases the air from the spring primary and secondary circuits flows to the relay valves brakes, allowing them to apply. (14) at the rear axles. This control pressure on the relay To release the spring parking brakes, the driver valves causes the relay portion of the valves to open, must move the control valve to the “release” position. This relaying air pressure to the brake chambers. When the directs air to the spring brake relay valve, which supplies foot valve treadle is released, air pressure in the control air pressure to the spring brakes, which lines between the foot valve and relay valves is released compresses or “cages” the springs and releases the brakes. through the exhaust ports in the foot valve. Air pressure in the brake chambers is released through large exhaust ports in the relay valves. Should either the primary or secondary SUPPLY circuit fail, the remaining circuit is isolated and continues to have braking ability. When either the primary or secondary SUPPLY circuit fails, braking on the front axle and one rear axle will not be affected due to the two way check valve (22) installed between the two service circuits.

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NUNAVUT AIR BRAKE MANUAL SECTION V

To apply the trailer brakes only, or for a higher brake L-75 OFF HIGWAY application on the trailer than on the tractor, the driver applies hand valve (21), air from the tanks flows through SYSTEM, COMBINATION the hand valve into a double-check valve (22), to the tractor protection relay valve (33). Brakes on the trailer WITH SCHEDULE X are then applied and released as described above. TRAILER If necessary, the trailer brakes can be “dynamited” by closing the trailer supply valve. This shuts off the air The L-75 tractor brakes are piped similar to the T-75 supply from the tanks and simultaneously exhausts the system. A low pressure governor (31), a dump valve (32), supply line into the atmosphere. Loss of air pressure in a hand valve (21), a two-way check valve (22) and a relay the supply line causes the trailer ’s relay emergency valves type tractor protection valve (33), have been added. In to dump full reservoir pressure into the brake chambers. this system, when air pressure rises to approximately 60 P.S.I., the low pressure governor opens, allowing air The trailer system will provide a rapid application and pressure to close the emergency dump valve. When release of the trailer brakes as each axle has its own air maximum air pressure is reached, the governor unloads tank and relay emergency valve. the compressor. If a brake chamber or air line ruptures on one axle, To fill the trailer tanks, the driver must open the trailer the other axle continues to have braking ability for supply valve (24) until the trailer supply line gauge (34) emergency stops. shows over 50 P.S.I. The trailer supply valve will then The L-75 tractor system has the same air loss safety remain open on its own, keeping the trailer tanks at the features as the T-75. same pressure as the tractor tanks. When a brake application is made with the foot valve, air flows through a two-way check valve (22) to the control port on the tractor protection relay valve (33), which relays air pressure from the supply line to the ser- SCHEDULE SX vice line. The service pressure line relays air from the trailer tanks through the relay emergency valves (25) to OFF HIGHWAY TRAILER the trailer brake chambers WITH SPRING BRAKES When the brakes are released, air pressure in the service line is exhausted through the exhaust port in the tractor The SX trailer brake system is piped similar to the Schedule protection relay valve. Air pressure in the trailer brake X system. Both systems provide air loss safety features. A chambers is exhausted through a large exhaust port in one-way check valve (9), a third tank (2), a spring brake the relay emergency valves. This action, both in applica- control valve (19), two four-line two-way check valves (35) tion and release, is simultaneous on tractor and trailer. and four spring brakes (18) have been added.

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SECTION V NUNAVUT AIR BRAKE MANUAL

The addition of spring brakes serves two functions. It pro- 8. What is blended air? vides a method of securing the trailer when parked and 9. Can a single circuit trailer be towed with dual acts as an emergency brake for the trailer axle that has lost circuit tractor? its supply reservoir pressure. (The trailer spring brakes 10. Name the components found on an L-75 system that are held off or caged by trailer supply reservoir pressure.) are not on a dual circuit “highway” system. If the trailer has lost all supply reservoir pressure and 11. If the trailer breaks away from the tractor on an L-75 must be moved, the spring brakes may be released by system, what applies the trailer brakes? opening the spring brake control valve 19) located at the (a) the trailer reservoir pressure rear of the trailer. This directs air from the isolated third (b) the spring brakes if equipped tank to release the spring brakes. The spring brakes may be reset by closing the spring brakes control valve. Care should be taken when moving the trailer as the service brakes will not apply. NOTES

SECTION SUMMARY 1. What is the basic principle of the dual circuit system? 2. What valve is used to protect the primary circuit from the secondary circuit? 3. In a simple dual circuit system, will the vehicle continue to have braking ability if one circuit fails? 4. Is there a difference between the foot valve used in a single circuit system and the foot valve used in the dual circuit system? 5. Name two functions of the spring brakes in a dual circuit system. 6. Describe the functions of the spring brake modula- tor valve. 7. If the trailer brakes away from the tractor on a dual circuit highway system, what applies the brakes on the trailer? (a) the trailer reservoir pressure (b) the spring brakes

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NUNAVUT AIR BRAKE MANUAL

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SECTION VI NUNAVUT AIR BRAKE MANUAL

SECTION VI PRE-TRIP INSPECTION SINGLE UNIT COMBINATION UNIT BRAKE ADJUSTMENT AIR OPERATED DISC BRAKES INSERVICE CHECK MAINTENANCE AND SERVICING OF AIR BRAKES SECTION SUMMARY QUESTIONS

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NUNAVUT AIR BRAKE MANUAL SECTION VI

Suggested maximum time required for this pre-trip PROCEDURE FOR AIR inspections 30 minutes. NOTE: Trailer tanks will not require draining for testing PRE-TRIP, SINGLE UNIT purposes only.

- SINGLE CIRCUIT OR CIRCLE CHECK DUAL CIRCUIT 1. Check security and condition of compressor and belts under hood. Check vehicle on level ground if possible, set parking 2. Check condition and security of hoses and flex lines brake, block wheels, ensure that all tanks are drained. and glad hands. Suggested maximum time required for this pre-trip 3. Pull all slack adjusters manually (use pry bar if nec- inspection is 15 minutes. essary). Check for travel, mechanical condition, wear.

CIRCLE CHECK NOTE: A brake adjustment (S cam type only) will be required as part of the Air Brake Examination. 1. Check security and condition of compressor ad belts under hood. BUILD UP AIR PRESSURE, WATCHING THAT THE: 2. Check condition and security of hoses and flex lines. 1. Warning device cuts out at approximately 60 P.S.I.; 3. Pull all slack adjusters manually (use pry bar if nec- 2. Pressure builds from 50 -90 P.S.I. within five minutes; essary). Check for travel, mechanical condition, wear. 3. Governor cuts out between 105 P.S.I. minimum and 4. On spring brake equipped vehicles, check angle of 125 P.S.I. maximum. push rod and slack adjuster arm does not exceed 90°. 4. Release spring brakes. NOTE: A brake adjustment (S cam type only) will be Charge trailer and rebuild pressure if necessary. required as part of the Air Test Examination. BRAKE SUPPLY LINE: BUILD UP AIR PRESSURE, WATCHING THAT THE: 1. Trailer brakes should apply. 1. Warning device(s) cuts out at approximately 60 P.S.I.; 2. There should be no air loss from trailer. 2. Pressure builds from 50 - 90 P.S I. within five minutes; 3. Air from the tractor 3. Governor cuts out between 105 P.S.I. minimum and (a) stop immediately; mandatory on L75 or, 125 P.S.I. maximum. (b) bleed down to between 45 -20 P.S.I., then stop. AT MAXIMUM PRESSURE: NOTE: Under no circumstances should tractor pressure 1. Release parking brakes (if equipped) to prevent drain below 45 - 20 P.S.I. compounding. Reconnect supply line and recharge trailer. Rebuild pressure if 2. Shut off motor. necessary. 3. Make a full brake application. Check for: BREAK SERVICE LINE: (a) air loss less than 3 P.S.I. drop within one minute (b) audible air leaks. No air should escape. Make a full brake application. 1. Trailer brakes should apply immediately and there START MOTOR AND FAN BRAKES will be no further loss of air from the service line; 1. Stop fanning at 80 P.S.I. to see if governor has cut in mandatory on L75 or: (needle should start to climb). 2. Tractor air will bleed down to 45 - 20 P.S.I. and then 2. Continue fanning: trailer brakes will apply with no further air loss (a) warning device should start operating at approx- from the service line. imately 60 P.S.I.; Reconnect service line, charge trailer and rebuild pressure to (b) parking brake should apply at 45 -20 P.S.I. if maximum reservoir pressure. plumbed into main reservoir tanks. AT MAXIMUM PRESSURE: REBUILD PRESSURE TO MAXIMUM 1. Release parking brakes. 2. Shut off motor. 1. With parking brakes set, remove wheel chocks. 3. Make a full brake application, check for: 2. Gently tug test against parking brakes in low gear. (a) air loss less than 4 P.S.I. drop within one minute; 3. Release parking brakes and move vehicle ahead (6 P.S.I. with 2 trailers) slowly and make a service brake application to (b) audible air leaks. check the brake response. START MOTOR AND FAN BRAKES. PROCEDURE FOR AIR PRE- 1. Stop fanning at 80 P.S.I. to see if governor has cut in (needle should start to climb). TRIP, COMBINATION UNIT - 2. Continue fanning: (a) warning device should start operating at 60 P.S.I.; SINGLE OR DUAL CIRCUIT (b) trailer brakes should apply between 45 -20 P.S.I. (L75 must apply at 50 P.S.I.); Check vehicle on level ground if possible, set parking (c) parking brakes should apply at 45 -20 P.S.I., if brake, block wheels, ensure that all tanks are drained. plumbed into main reservoir tanks. 52

SECTION VI NUNAVUT AIR BRAKE MANUAL

REBUILD PRESSURE TO MAXIMUM. may appear to be working at slow speeds on light air application. THE ONLY WAY TO BE SURE THAT YOUR 1. With parking brakes set, remove wheel chocks. VEHICLE BRAKES ARE PROPERLY ADJUSTED IS TO 2. Gently tug test against parking brakes in low gear. PHYSICALLY CHECK EACH WHEEL. 3. Release parking brakes and set trailer brakes with the hand valve. Gently tug test against the trailer brakes in low gear. 4. Move vehicle ahead slowly and make service brake IN SERVICE CHECKS application to check brake response. STEEP DOWNGRADE: In some areas of Nunavut, signs such as the following are posted in advance of steep or long downgrades: BRAKE ADJUSTMENT All drivers should be trained to make brake adjust- ments. If a driver must adjust the brakes on his/her vehicle (at a mandatory brake check sign for example), the fol- lowing steps are recommended for “S” cam brakes: 1. Block the wheels, release spring brakes and shut off the engine, leaving it in low gear. Check the push rod travel by pulling on a slack adjuster by hand or with a pry bar. If on common brake chamber, slack (push rod 3 travel) exceeds /4 inch brake adjustment is required. CAUTION: A strong physical pull is necessary to move all the slack out of the travel. 2. After determining that brake adjustment is necessary: (a) Use a proper wrench to disengage the external locking device (if so equipped) from the adjust- ment bolt of the slack adjuster. Such signs indicate that the driver must stop his vehicle (b) Turn the adjustment bolt until the lining con- in the pull-out area and inspect his/her vehicle’s braking tracts the drum. If possible, visually check to see sys- tem before proceeding. Check: that the brake linings are in contact with the brake drum. 1. Compressor is maintaining full reservoir pressure. (c) When turning the adjustment bolt on the slack adjuster, the spline on the S cam shaft should 2. Push rod travel is within limitations on all chambers. turn in the same direction as if a brake applica- 3. No audible air leaks. tion were being made. 1 1 4. Glad hands and lines are secure. (d) Back the adjustment bolt about /4 to /2 of a turn. This should result in proper adjustment. 5. Drums, bearings and tires are not overheating. (e) No re-check for free play of slack adjuster travel. 1 3 6. Trailer supply valve is operating properly. The travel should now be between /2 and /4 of an inch. If travel is checked by watching the push rod while someone makes a brake applica- The driver must be aware of the condition of his/her 1 tion, travel should not exceed 1- /2 inches. vehicle’s braking system at all times. He can do this by: NOTE: Please see page 15 for automatic slack adjusters. 1. SEEING the pressure gauges;

2. HEARING the warning signals; and 3. FEELING the braking response of the vehicle. AIR OPERATED DISC BRAKES By these methods of observation, the driver should be able to notice any defects developing in the braking These brakes require special adjustment to the manufac- system and be aware that service or adjustment are required. turer ’s specifications. Ensuring that the vehicle is in proper condition to drive ALL BRAKES is the responsibility of everyone involved. The extent of the driver ’s responsibility to make repairs will depend At the first stop after adjusting the brakes, check each on many factors, such as: brake drum or rotor for temperature. An extra hot brake The maintenance policy of the company; drum indicates that you have adjusted it too tightly. The driver ’s mechanical experience; Only when all brakes are properly adjusted will the sys- tem be able to absorb the required amount of energy to Whether or not the vehicle is operator owned; and, bring the loaded vehicle to a safe stop under extreme The availability of repair service. conditions. Remember that poorly adjusted air brakes 53

NUNAVUT AIR BRAKE MANUAL SECTION VI

MAINTENANCE AND METRIC SERVICING OF THE AIR CONVERSION BRAKE SYSTEM TABLE As several of the newer trucks now have air gauges PLACING THE VEHICLE IN SERVICE indicating pressure in kilopascals (kPa), the following Before placing a vehicle into service, specific items must conversion chart may help.

be checked to ensure the vehicle is in satisfactory condi- tion. Preventative maintenance checks are designed to prevent mechanical failures which could result from CONVERSION CHART neglect. These checks cut repair costs by detecting minor kPa Lbs. kPa Lbs. Lbs. kPa Lbs. kPa mechanical defects which would otherwise develop into 3 major breakdowns! 5 /4 300 43 1 6.9 60 414 1 Items to be checked include: 10 1 /2 350 51 2 13.8 65 449 1 Cooling system level and condition 15 2 /4 400 58 3 20.7 70 483 Fan and compressor drive belts 20 3 450 65 4 28 75 518 Crankcase oil level and leaks 1 Batteries, electrolyte level 25 3 2 500 72 5 34.5 80 552 1 Fuel tanks and gauges 30 4 4 550 80 6 41.4 85 587 Tires and wheels Lights, signals, horn 35 5 600 87 7 48.3 90 621 3 Windshield, wipers, mirrors 40 5 4 650 94 8 55 95 655

Steering 1 45 6 2 700 101 9 62.1 100 690 Emergency equipment 1 BRAKES, service and park 50 7 4 750 109 10 69 105 725 3 4 110 759 60 8 800 116 15 103 See Professional Driver’s Manual for details. 70 10 850 123 20 138 115 794 Preventative maintenance may be assigned to a 1 80 11 2 900 130 25 173 120 828 maintenance crew or to the driver, but one person alone is finally responsible to ensure that the 90 13 950 138 30 207 125 863 1 braking system is in operating condition before the 100 14 2 1000 145 35 242 130 897 vehicle moves: THE DRIVER IS RESPONSIBLE. 150 22 1050 152 40 276 135 932

200 29 1100 159 45 311 140 966 250 36 50 345 145 1000 SECTION SUMMARY 55 380 150 1035

1. What is the maximum time permitted for the compressor to build from 50 P.S.I. to 90 P.S.I. ? 2. What is the maximum pressure loss permitted on full brake application with the motor shut off? 3. How can the holding power of the trailer brakes be tested? 4. Should all drivers be able to adjust “S” cam and drum braking systems? 5. What is the final brake test that should be made before the vehicle is put into service? 6. What test must be made at a “truck stop here” sign posted before a steep or long downgrade? 7. What are three ways to check the condition of a vehicle’s braking system? 8. Is a brake adjustment part of the air brake test given by the Motor Vehicles Division? 9. Do the brake adjustment specifications differ between the “S” cam and drum system and the disc brakes system? 10. When should the brakes be checked after an adjust- ment has been made? 54

SECTION VI NUNAVUT AIR BRAKE MANUAL

NOTES NOTES

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NUNAVUT AIR BRAKE MANUAL SECTION VI

NOTES NOTES

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SECTION VI NUNAVUT AIR BRAKE MANUAL

NOTES NOTES

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NUNAVUT AIR BRAKE MANUAL SECTION VI

NOTES NOTES

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