Chettinad College of Engineering and Technology

CHETTINAD COLLEGE OF ENGINEERING AND TECHNOLOGY ME2305 APPLIED HYDRAULICS AND PNEUMATICS Prepared by B.BALASUBRAMANIAN ASSISTANT PROFESSOR DEPARTMENT OF MECHANICAL ENGINEERING

UNIT – I FLUID POWER SYSTEMS AND FUNDAMENTALS Introduction to fluid power:  Fluid power is the technology that deals with the transmission of energy by means of enclosed pressurized fluids.  Fluids can be either a liquid or a gas  Fluid power in general includes hydraulics and Pneumatics.  Hydraulic systems operate at a pressure of 200 bar or even much higher and so hydraulics are preferred in high load applications.  Pneumatic system operates at a pressure range from 5 to 10 bar and so pneumatics can produce only low or medium size forces.  Fluid power systems are used widely due to their ability to do useful work economically and efficiently. Perhaps the greater advantage of these systems is the flexibility with which power can be distributed and applied easily to the point of work. Advantages of fluid power systems:  The fluid power drives are more compact than a mechanical drive because it eliminates the need for links like cams and gears.  Multiplication of small forces to achieve greater forces.  Speed control is easy.  Accuracy in controlling small or large forces is possible with hydraulic systems.  Constant force is possible in fluid power systems regardless of special motion requirements.  As the medium of power transmission is fluid, it is not subjected to any breakage of parts as in mechanical transmission.  The parts of hydraulic systems are lubricated with the hydraulic liquid itself.  Overloading can be more easily controlled by using relief valves.  Air equipment reduces the danger of fire and explosion hazard in industries.  Simplicity and compact.  Cost is relatively low for power transmission’s Applications of fluid power systems:  Agriculture – Tractors and farm equipment’s like ploughs, mowers, chemical sprayers, fertilizer spreaders, hay balers etc.,  Automation – Automated transfer machine  Aviation – Landing wheels on airplanes and helicopter, aircraft trolleys  Construction equipment’s – Earth moving equipment’s like excavators, bucket loaders, dozers, crawlers, post hole diggers, road graders.  Entertainment – Amusement park rides like roller coaster.  Fabrication industry - Hand tools like pneumatic drills, grinders, borers, nut runners  Glass Industry – Vacuum suction cups for handling  Material Handling – Jacks, hoists cranes, forklifts, conveyor system.  Medical – breathing assistors, heart assist devices, cardiac compression machine, dental drills and human patient simulator  Mining – rock drills, excavating equipment’s, ore conveyor loaders,  Press tools – heavy duty presses for bulk metal forming, lighter presses for sheet metal bending, punching, stamping etc.,  Robots – fluid power operated robots, pneumatic grippers  Transportation – hydraulic elevators, winches, overhead trams.  Vehicle – power steering, power brakes, hydraulic/air-oil suspension system. Types of fluid power systems: Fluid power systems can be categorized in different ways 1. Based on the control system used  Open loop system  Closed loop system 2. Based on the type of control  Fluid logic control  Electrical control  Electronic control Based on the control system used: Open loop system:  Open loop system does not use feedback.  The performance is based on the characteristics of individual components of the system.  It is not as accurate as closed loop system.  The error can be reduced by careful calibration. Closed loop system:  Closed loop system uses feedback.  Simple closed loop systems uses servo valves and advanced system uses digital electronics  High accuracy. Based on the type of control

Fluid logic control:  This type of system is controlled by hydraulic oil or air.  The system employs fluid logic devices such as AND, NAND, OR, NOR, etc.  Two types of fluid logic systems are available: (a) Moving part logic (MPL): These devices are miniature fluid elements using moving parts such as diaphragms, disks and poppets to implement various logic gates. (b) Fluidics: Fluid devices contain no moving parts and depend solely on interacting fluid jets to implement various logic gates.

Electrical control:  This type of system is controlled by electrical devices.  Four basic electrical devices are used for controlling the fluid power systems: switches, relays, timers and solenoids.  These devices help to control the starting, stopping, sequencing, speed, positioning, timing and reversing of actuating cylinders and fluid motors.  Electrical control and fluid power work well together where remote control is essential.

Electronic control:  This type of system is controlled by microelectronic devices.  The electronic brain is used to control the fluid power muscles for doing work.  This system uses the most advanced type of electronic hardware including programmable logic control (PLC) or microprocessor (µP).  In the electrical control, a change in system operation results in a cumbersome (complicated) process of redoing hardware connections.  The difficulty is overcome by programmable electronic control.  The program can be modified or a new program can be fed to meet the change of operations.  A number of such programs can be stored in these devices, which makes the systems more flexible.

Properties of fluids:

1. Viscosity: Viscosity is the measure of the fluid internal resistance offered to flow. 2. Viscosity index: The rate of change of viscosity with temperature is indicated on an arbitrary scale called viscosity index. The lower the viscosity index, the greater the variation in viscosity with change in temperature and vice versa. 3. Oxidation Stability: oxidation is caused by a chemical reaction between the oxygen of the dissolved air and oil. It creates impurities like sludge, insoluble gum and soluble products make the operation sluggish. 4. Demulsibility: The ability of hydraulic oil to separate rapidly from moisture and successfully resists emulsification is known as Demulsibility. 5. Lubricity: At the time of selecting a hydraulic oil care must be taken to select one which will be lubricate the moving parts efficiently. 6. Rust prevention: the moisture entering the hydraulic system with air causes the parts made ferrous materials to rust. So additives named “inhibitors” are added to the oil to keep the moisture away from the surface. 7. Pour point: The lowest temperature at which the oil is able to flow easily. 8. Flash point: The temperature at which a liquid gives off vapour in sufficient quantity to ignite momentarily or flash when a flame is applied. 9. Fire point: The minimum temperature at which the hydraulic fluid will catch fire and continues burning. 10. Neutralisation number: The neutralisation number is a measure of the acidity or alkalinity of a hydraulic fluid. This is referred to as the PH value of the fluid. High acidity causes the oxidation rate in an oil to increase.

General Types of fluids:

1. Water: water is treated with chemicals before being used in a fluid power system. It removes the undesirable contaminants. Advantages: Inexpensive, readily available, fire resistance. Disadvantages: No lubricity, corrosive, temperature limitations.

2. Petroleum oil: These are the most common among the hydraulic fluids which are used in a wide range of hydraulic applications. Advantages:Excellent lubricity, reasonable cost, non-corrosive Disadvantages:Tendency to oxidise rapidly, not fire resistant.

3. Water Glycol: Solutions of water and glycol and they contain 35 to 55 percent of water. Advantages: Good fire resistance, inexpensive, compatible with most pipe compounds and seals Disadvantages: Not good for high bearing loads, poor corrosion resistance

4. Water oil Emulsion: They contains 40% water. The rest is oil, emulsifiers and other additives. The water is dispersed in microscopic droplets surrounded by a film of oil. Advantages: Good fire resistance, inexpensive, compatible with most seals Disadvantages: Sometimes difficult to maintain

5. Phosphate ester: Organic alcohols attached to a phosphorous atom. Advantages: Excellent fire resistant, good lubricity, non-corrosive Disadvantages: Not compatible with many plastics and elastomers, fairly expensive Silicone: Dimethyl polysiloxanes. Advantages: Non corrosive, nontoxic, less volatile, excellent thermal stability

Comparison between Hydraulics and Pneumatics Pascal’s Law: The pressure generated at one point in a confined liquid acts in all direction i.e. the pressure applied at one point in a confined liquid acts equally in all direction of the liquid. Laminar flow: The flow in which one layer of fluid will not interact with another layer of fluid. If the Reynolds number is less than 2000, the flow is laminar. Turbulent flow: the flow in which one layer of fluid interact with another layer of fluid. If the Reynolds number is greater than 4000, the flow is turbulent. Fluid power symbols: Refer R.SRINIVASAN book (Page No: 395 – 402) You are asked to draw the symbols in 2 Marks and 4 Marks.

Problems: Problems from first unit based on the following formulas  Reynolds Number  Darcy-Weisbach Equation (Head loss)  Continuity equation  Bernoulis equation  Friction factor  Pressure drop due to friction  Equivalent length of fittings  Total length of pipes  Density and specific gravity relation Most important thing is “READ THE QUESTION CAREFULLY” to know the difference between P1 and P2.

Types of questions:  Determine whether the flow is laminar or turbulent?  Determine the Head loss?  Determine the pressure drop?  Determine the pressure at exit or discharge or inlet?

Way of answering problems:  Given Data  To find  Formulas used  Solution  Result