Introduction to Fluid Power

Chapter 1 Introduction to Fluid Power The Fluid Power Field Since the beginning of time, long before written history, humankind has searched for ways to conveniently transmit energy from its source to where it is needed and then convert the energy into a useful form to do work. This chapter introduces the fluid power field as an approach that provides an effective means of transferring, controlling, and converting energy. Selected Key Terms Internet Resources The following names and terms will be used in www.ideaﬁ nder.com/history/inventors/watt.htm Objectives this chapter. As you read the text, record the mean- The Great Idea Finder After completing this chapter, you will be able to: ing and importance of each. Additionally, you may Provides information on James Watt and other inventors ■ use other sources, such as manufacturer literature, who made major contributions to industrial development Define the terms fluid power, hydraulic system, and pneumatic system. during the Industrial Revolution. ■ an encyclopedia, or the Internet, to obtain more Explain the extent of fluid power use in current society and provide information. www.island-of-freedom.com/pascal.htm several specific examples. actuator Island of Freedom ■ List the advantages and disadvantages of fluid power systems. Archimedes Provides details of the contributions of Blaise Pascal and others to science, mathematics, and philosophy. ■ Discuss scientific discoveries and applications important to the historical Bernoulli, Daniel www.nfpa.com development of the fluid power industry. Boyle, Robert Bramah, Joseph National Fluid Power Association Charles, Jacques A good overall review of the basic aspects of fluid power systems. Go to the Our Industry section of the site. compact hydraulic unit cup seal http://library.thinkquest.org/3044 da Vinci, Leonardo Oracle Education Foundation fluid compressibility Provides insight into Leonardo da Vinci as an artist and inventor. fluid power Hero www.en.wikipedia.org/wiki/hydraulic hydraulic www.en.wikipedia.org/wiki/pneumatic hydraulic accumulator Wikipedia: The Free Encyclopedia laminar Include information on history and operation of hydraulic and pneumatic power-transmission systems. Additional Pascal, Blaise sites are listed that can provide information on specific fluid pneumatic power system elements. pump Reynolds, Osborne Torricelli, Evangelista von Guericke, Otto water screw waterwheel Watt, James windmill

15 16 Fluid Power Chapter 1 Introduction to Fluid Power 17

(source) to an actuator that completes the task Modern farm equipment uses hydraulics exten- Definition of Fluid Power (work) required of the system. sively. These uses range from simple hydraulic cyl- Fluid power systems use the prime mover to inders that raise and lower implements to complex The basis of fluid power is pressurized fluids. drive a pump that pressurizes a fluid, which is then devices that maintain clearances, adjust torque, These fluids may be either liquids or gases. The transferred through pipes and hoses to an actua- and provide easy control of speed and direction fluids are incorporated into physical hardware tor, Figure 1-2. Mechanical systems transfer power on tractors and a variety of specialized planting, systems that generate, transmit, and control power from the prime mover to the point of use by means harvesting, and processing equipment. in a wide variety of consumer and industrial appli- of shafts, belts, gears, or other devices. Electrical Fluid power is used in some form in all modern cations. Today, it would be difficult to identify a systems transfer power using electrical current transportation systems designed to move people product that has not been affected by fluid power flowing through conductors. Typical applications and products. These uses range from automobiles at some point along the route from raw material to in business, industrial, and consumer products to complex, wide-body aircraft found on inter- final installation. and systems use combinations of fluid, mechani- national flights. Specific examples of the applica- Fluid power systems are versatile contributors cal, and electrical power transfer methods. tion of fluid power principles include hydraulic to industry. Applications range from brute force and pneumatic braking systems, power-assisted needed in heavy industry to the sensitive position- steering found on most forms of wheeled vehicles, ing of parts in precision machining operations, hydrostatic transmissions that provide almost Figure 1-1. The systems are generally grouped Fluid Power Industry unlimited speed and torque control, and suspen- under the two broad classifications of pneumatic sion systems that use hydraulic and/or pneumatic and hydraulic. Pneumatic systems use gas, usu- The fluid power industry is a complex entity. Figure 1-3. The service of fl uid power systems in dampening. ally air, while hydraulic systems use liquids, usu- It includes education, design and manufacture of business and industry provides employment for The construction industry is a very diverse ally oil. Other fluids are often used in special components, design and assembly of systems using many highly trained individuals. industry. Construction activities include the applications. those parts, and troubleshooting and maintenance (Photo: Atlas Copco) building of residences and all types of commer- Fluid power is one of the three types of power needed to keep the systems performing efficiently, cial structures, roads and highways, irrigation transfer systems commonly used today. The other Figure 1-3. In addition, a complex sales and distri- systems, harbor facilities, and a wide variety of systems are mechanical and electrical. Each of bution system assures users access to replacement other construction-related activities. The industry the systems transfers power from a prime mover components and information concerning service, Growth of the fluid power industry has makes use of many types of earth-moving equip- new and improved component designs, and new required a parallel growth in the number of peo- ment, material-handling equipment, and special- system applications. ple who understand and can work effectively with ized fastening and finishing devices. Examples of fluid power systems. These people range from typical applications that make use of fluid power engineers responsible for designing the compo- include: backhoes for excavation; cranes for mov- nents to mechanics responsible for maintenance ing, lifting, and positioning materials; vibrators and repair of fluid power equipment. The type of for consolidating concrete after it has been placed; education and training available to prepare these and nail-driving apparatuses. people varies considerably. Formally organized Manufacturing organizations extensively programs exist in two-year technical and com- rely on fluid power. Applications range from munity colleges, four-year universities, and in huge presses in automobile body fabrication programs offered by component manufacturers. plants, which form body panels, to packaging Many individuals seek fluid power training after equipment for miniature parts in electrical com- exposure to the field through their jobs. ponent manufacturing operations. These appli- The fluid power industry is a broad field and a cations use hydraulics and pneumatics to make key contributor to the success of many businesses the equipment operate as needed. Required and industries. Fluid power is extensively used characteristics range from huge forces to draw in manufacturing, construction, transportation, metal into desired shapes, to a gentle nudge agriculture, mining, military operations, health, accurately positioning a part for machining, to and even recreation. The list is almost endless. the deliberate movement of sanders performing Applications vary and components have different a final finish sanding. Fluid power can easily Figure 1-1. Equipment used in construction and appearances in the various applications. System provide each of these characteristics. In many street maintenance is an example of a fl uid power sizes range from miniature to massive, but fluid installations, the desired results can be obtained application commonly encountered in daily life. This Figure 1-2. Many consumer items make use of fl uid power principles provide the needed power, force, using off-the-shelf equipment. In many other backhoe is capable of producing the brute force power in their operation. This garden tractor has a and control. situations, standard components may be used needed to break and move concrete. hydrostatic transmission. (Used with permission of Fluid power has been a key contributing factor in to assemble circuits and systems to produce the (Deere & Company) CNH America LLC) the development of current agricultural equipment. desired result, Figure 1-4. 18 Fluid Power Chapter 1 Introduction to Fluid Power 19

civilian commercial applications, but others are is further complicated by the inherent differences Component weight highly specialized and are not directly duplicated of the two major divisions of the fluid power field: System operating pressure affects the struc- in commercial applications. Hundreds of applica- hydraulics and pneumatics. ture of components. Hydraulic systems operate tions exist, ranging from power-assisted steering at higher pressures, requiring the use of stronger of land vehicles to the precision positioning of System Characteristics materials and more-massive designs to withstand rocket launchers for air defense, Figure 1-5. the pressure. Pneumatic systems operate at much Although hydraulic and pneumatic systems lower pressures and, therefore, can be manufac- share the characteristics of energy transfer by tured using lightweight materials and designs that Fluid Power Systems means of fluid pressure and flow, differences minimize the amount of material. affect how and where they are applied. These dif- Hydraulic applications tend to involve equip- Fluid power is a highly versatile power trans- ferences include: ment that handles heavier weights, requiring mission system, as illustrated by the range of ■ Accuracy of actuator movement both higher system operating pressure and physical strength of machine parts. Figure 1-6 shows applications discussed earlier in this chapter. No ■ Operating pressure system, however, is entirely suitable for all applica- a front-end loader. The cylinders used to operate ■ tions. All power-transmission systems have char- Actuator speed the bucket must be of a construction that can with- acteristics that are desirable in one application, but ■ Component weight stand high system pressure and the heavy load of the bucket and its contents. turn into disadvantages in other situations. A sys- ■ Cost tem cannot have every desired advantage without Pneumatic systems tend to involve applications where ease of handling and lightweight disadvantages. Understanding system characteris- Accuracy of movement Figure 1-4. Fluid power applications have been tics as well as what is needed for a particular result are critical for effective operation of the tool or used during the manufacture or processing of most will help in producing an effective and efficient Fluid compressibility is the inherent char- system. Figure 1-7 shows a pneumatic grinder consumer products today. This carnival ride makes application. acteristic that produces the difference between being used on a large metal casting. The grinder © extensive use of ﬂ uid power. ( 2007 Jupiterimages The range of applications that use fluid power hydraulic and pneumatic systems. A gas is com- is lightweight and very portable. The tool is easily and its licensors. All rights reserved.) makes the development of a simple list of advan- pressible, while a liquid can be compressed only manipulated by an individual and constructed to tages and disadvantages difficult, since examples slightly. Hydraulic systems, therefore, can produce provide a long service life. that do not “fit” can easily be found. This problem more accurate, easily controlled movement of cylinders and motors than pneumatic systems. Com- Mining companies use fluid power both in pressibility produces a more “spongy” operation open-pit and underground operations. Spectacular in pneumatic systems that is not suitable where examples of an application in this industry are the highly accurate movement is required. huge shovels used in coal strip mining operations. These shovels remove the overburden from veins of Operating pressure coal that are near the surface. Some of these shovels are several stories high and they can remove mul- Hydraulic systems can operate at much higher tiple cubic yards of material during each pass of pressures than pneumatic systems. Hydraulic sys- the scoop. The shovels use large numbers of fluid tem operating pressure ranges from a few hundred power systems and circuits for movement and con- pounds per square inch (psi) to several thousand trol. Other open-pit mining operations use more psi. Pressures of more than 10,000 psi are used in standard front-end loader and truck designs for special situations. Pneumatic systems, in contrast, loading and moving ore. In addition, many fluid normally operate between 80 to 120 psi. Extremely power applications, both pneumatic and hydrau- high–pressure pneumatic systems normally are lic, can be found in mine drilling, crushing, and not used. material-handling equipment. Fluid power applications are especially desirable in underground Actuator speed mining locations. Accumulations of gas may pro- Pneumatic systems are commonly used when duce potentially explosive conditions, limiting or high-speed movement is required in an applica- preventing the use of electrical devices. tion. Rotation speeds of over 20,000 revolutions Land, sea, and air defense forces use fluid per minute (rpm) are possible. Rapid-response power to assist in moving personnel, supplies, cylinder operation is also possible with pneumatic Figure 1-6. Hydraulic systems are commonly used and equipment to support their operations. The Figure 1-5. Complex defense systems make exten- systems. These designs are generally found in sit- in applications where high system pressures are military makes use of a full range of fluid power sive use of ﬂ uid power. (©2007 Jupiterimages and uations involving lighter loads and lower accuracy needed to complete the required work. components and circuits. Many of these parallel its licensors. All rights reserved.) requirements. (Deere & Company) 20 Fluid Power Chapter 1 Introduction to Fluid Power 21

Advantages ■ Large volumes of compressed air may be ■ Special handling and disposal procedures The following list of advantages applies to both easily stored in pneumatic systems to pro- for hydraulic oil required by environmental hydraulic and pneumatic systems, except as noted. vide energy for intermittent, heavy system regulations. demand, Figure 1-9. ■ ■ An easy means of multiplying and controlling High cost of compressing and conditioning ■ force and torque. Pneumatic systems provide clean operation air for use in pneumatic systems. with minimal fire hazard. ■ ■ Infinitely variable speed control for both lin- Reduced accuracy in actuator speed control in ear and rotary motion. pneumatic systems caused by compressibility Disadvantages of air. ■ Overloading the system simply stalls the actu- ■ ator without damage to the components. The following list of disadvantages applies to both Noise level of pneumatic systems when air hydraulic and pneumatic systems, except as noted. ■ is directly exhausted to the atmosphere from Provides an easy means of accurately control- ■ components. ling the speed of machines and/or machine Higher safety factors associated with parts. high-pressure oil and compressed air. ■ ■ Provides the ability to instantly stop and Susceptibility to dirty environments, which reverse linear and rotary actuators with mini- can cause extreme component wear without Historical Perspective of mal shock to the system. careful filtration. ■ Fluid Power ■ Systems easily adapt to accommodate a range Fluid leakage and spills cause a slippery, messy work environment around hydraulic Figure 1-7. Pneumatics are commonly used where of machine sizes and designs. Awareness of the historical background of our equipment. high speeds and lightweight tools are needed. ■ civilization, our particular culture, and our nation Systems readily adapt to external control ■ are generally considered an important part of the (Photo: Atlas Copco) methods, including mechanical, pneumatic, Fire hazard with hydraulic systems using combustible oils. preparation to be a responsible citizen. This aware- electrical, and electronic systems, Figure 1-8. ness provides an appreciation of our current situ- ■ Systems can easily provide component ation by providing information about the origin Cost lubrication. and development of cultural, religious, and politi- cal ideas, principles, and systems. Likewise, an The cost of fluid power systems ranges widely. awareness of the historical development of a tech- A variety of situations exist and a number of nical field of work should provide an appreciation solutions are available for each one. The solution of what we have, some idea of how it was achieved, selected to solve the problem directly affects the and an appreciation of the cultural changes associ- cost. Understanding system advancements, basic ated with the technical field. characteristics of hydraulic and pneumatic sys- This section provides a brief discussion of some tems, and knowing which standard components aspects of technical development and innovation are available are necessary to produce a system as viewed by Western culture. Volumes of infor- that does the best job at the lowest cost. mation are available on developments throughout The cost of system operation is a factor that history involving Islamic and Eastern contribu- must be considered. Generally, pneumatic systems tions as well as those reflecting Western thought. are more expensive to operate than hydraulic sys- Fluid power, as the term is currently used in our tems. This cost can be directly associated with the society, describes a relatively new field. However, compression, conditioning, and distribution of the roots of this field extend far back into history. air. Careful maintenance to eliminate leakage can greatly reduce operating cost. Historical Awareness Advantages and Disadvantages of The use of fluid power has developed along with Fluid Power Systems civilization. The natural movements of air and water were probably the first sources of power used by Fluid power systems have several advantages early humans. It is speculated that the use of crude and disadvantages when compared with mechani- Figure 1-9. Pneumatic systems can easily store sails to reduce the effort to move boats was the first cal and electrical power transfer systems. Several Figure 1-8. Both hydraulic and pneumatic systems large volumes of compressed air to meet the inter- attempt to harness this natural power, Figure 1-10. of the important advantages and disadvantages of can be readily adapted to external control systems, mittent high demand of some systems. The vertical These early applications were followed by the devel- fluid power systems are presented in the next two including state-of-the-art electronic designs. tank on the right serves as a storage area for com- opment of more sophisticated systems, which even- sections. (Photo: Atlas Copco) pressed air. (Photo: Atlas Copco) tually lead to the development of the windmill. 22 Fluid Power Chapter 1 Introduction to Fluid Power 23

It is doubtful whether the physical principles associated with modern hydraulics and pneumatics were fully understood in early history or even at the beginning of the Industrial Revolution. The physical principles and design features that we consider basic to the operation of fluid power systems were developed over several centuries. Many of these developments were the products of tinkerers more than due to an understanding of advanced scientific principles. Application of the scientific method played an ever-increasing role in the development of both fluid power theory and machinery design. The scientific method dictates Figure 1-11. Archimedes is credited with the design accurate measurement, controlled testing, repro- of the water screw, which has been used to move ducibility of results, and systematic demonstration and lift water since the third century BC. The basic and reporting of results. principles found in this device are still used in modern fl uid power components. (©2007 Jupiterimages and its licensors. All rights reserved.) Individuals in History Figure 1-10. People have used the natural move- Figure 1-12. Blaise Pascal developed during the The identity of individuals involved in the ment of both air and water throughout history to the device was considered to be an interesting toy, 1600s what is now called Pascal’s law. He is one original development of the significant fluid reduce work and aid in transportation. Using sails rather than a practical machine. His more practi- of a number of individuals who worked during the power scientific principles has been lost to time. on ships is an example of using fl uid power (wind). cal and enduring contributions relate to basic con- fi fteenth through the eighteenth century identifying One of the factors that makes the identification (©2007 Jupiterimages and its licensors. cepts of fluid flow and the study of the principles and proving basic principles by using the scientifi c of individuals difficult is that many of the prac- All rights reserved.) of the siphon. method. (©2007 Jupiterimages and its licensors. tical solutions were considered below the dignity Leonardo da Vinci is a name commonly associ- All rights reserved.) of “pure” science and, therefore, never recorded. ated with the fine arts, but he also must be consid- Several individuals, however, need to be recog- ered an equal genius in many other fields. During Flowing water in rivers and streams was also nized as having made important discoveries. Other the latter part of the fifteenth and early part of the used to assist in transporting boats and materials. individuals contributed by bringing together a hydraulic press: multiplication of force, and piston sixteenth centuries, he worked extensively in the The Egyptians, Persians, and Chinese built dams, group of known elements to form a principle that movement relationships. engineering and architectural fields in Italy and ditches, and gates to form elaborate water-control has become basic to the fluid power field. France. He made many contributions in the fields The English scientist Robert Boyle (1627–1691) and irrigation systems. These various applications Archimedes is credited with the discovery of mechanical design and fluid mechanics that was one of the first to work with the characteris- eventually led to the development of variations of of the principle of buoyancy in the third century involved the flow of water, hydraulic machinery, tics of gases. He referred to this as the “springi- the waterwheel to lift water for irrigation purposes BC. Folklore relates that discovery to the need to and principles that closely match the later work ness of air.” By direct measurement, he was able and turn simple mills. These early uses of fluid establish the amount of gold in the king’s crown. of Pascal. As with many other early scientists, his to establish: power were dependent on vast quantities of low- Archimedes did extensive work with mathemat- work was recorded as private notes, many of which If the temperature of a dry gas is pressure air and water supplied by nature. They ics and other scientific principles. Two volumes of have been discovered only in recent years. held constant, its volume inversely also were subject to variations in the weather, his known manuscripts deal with hydrostatics and Blaise Pascal is usually credited with the basic varies with its pressure. which made them somewhat unpredictable and floatation. He is also credited with the invention of principle that is the foundation of the fluid power only partially under the control of the operators. the water screw, Figure 1-11. This device has been Today, this principle is referred to as Boyle’s law. industry, Figure 1-12. During his relatively short The windmill and waterwheel were exten- used to lift and move water for centuries. It has life (1623–1662), he experimented extensively with As in most other situations where new laws or sively used as power generating devices before also greatly influenced the development of pump- liquids and mechanical devices, including siphons, principles are under development, Boyle was not and through the early years of the Industrial Revo- ing devices in the fluid power field. syringes, and tubes. This work produced the proof the only person to do fundamental work in the lution. Their power-generating capabilities were Hero is another individual who is recognized that many previous mathematicians and scientists area of gases. Otto von Guericke (1602–1686) from very limited, however, usually in the 5–10 horse- as contributing basic knowledge to the area of fluid had sought: Germany was also involved in experimentation power range with a maximum of 30 horsepower. mechanics. His work appears to have been done in with gases. He developed a vacuum pump in 1650. The development of large industrial complexes the second century BC, although no specific dates In a fluid at rest, pressure He used this pump to demonstrate the pressure of needed a larger and more-controllable power gen- have been established. Historians often considered is equally transmitted in all the atmosphere by pumping the air from a sphere erating system, such as the steam engine devel- him to be a recorder of information, rather than an directions. constructed of two equal parts. Once the air had oped by James Watt. This steam engine was not originator. Nevertheless, Hero is popularly identi- He is also credited with demonstrating and been removed, the pieces could not be pulled apart constructed until 1775. fied with a rotating, steam-jet device. At the time, clearly defining the principles involved in the by horses. 24 Fluid Power Chapter 1 Introduction to Fluid Power 25

An Italian, Evangelista Torricelli (1608–1647), Applications of Fluid Power world, especially in Persia. The most common is recognized as having identified the principles design, the water screw, is still used in parts of that affect fluid flow. He also did extensive work in through History Egypt and other areas of the world for moving or the field of mechanics and had an influence on the Fluid power as it is know today has been under lifting small volumes of water. The Roman Empire development of many scientific principles. Today, development for thousands of years. It has experi- constructed great aqueducts for the movement of he is generally associated with the development of enced rapid growth since the onset of the Indus- water. Ruins of these systems can still be found the barometer. However, close analysis of histori- trial Revolution. The previous section introduced throughout the territories the Romans controlled, cal data indicates the basic principles were tested some of the many individuals credited with identi- Figure 1-14. by others with Torricelli properly interpreting the fying the basic concepts that resulted in continued It is generally believed that the energy of run- results. industrial growth. This section presents some of ning water was first effectively harnessed dur- The French scientist Jacques Charles (1746– the concepts and applications of fluid power from ing the first century BC. Early waterwheels used 1823) provided another key element to under- a historical perspective. a horizontal wheel rotated by a running stream. standing fluid power principles. He developed a These designs typically developed one-half horse- law relating to the effect of temperature on the vol- power or less. Roman engineers developed verti- ume of a gas: Antiquity cal wheels that produced up to three horsepower. All gases expand or contract in The origins of fluid power are difficult to iden- These wheels used both undershot and overshot direct proportion to the change in tify. Recorded evidence does not exist and the designs. Undershot wheels were placed directly in absolute temperature. relationships that eventually produced important a stream. Overshot wheels used water directed on the top of the wheel through sluice channels from Charles’ law combined with Boyle’s law form the developments are not evident in most cases. Arche- Figure 1-13. James Watt perfected the steam dams or natural waterfalls. Waterwheels revolu- general gas laws, which are fundamental to any ology gives us many hints, but speculation still engine and greatly infl uenced the development of tionized the grinding of grain and were gradually calculations done for gases today. plays a major role in our current thinking about the Industrial Revolution. Many of his ideas were how existing scientific principles and mechanical adapted to other purposes. Daniel Bernoulli (1700–1782) is credited with used in the development of pumping devices. devices were developed. The use of windmills for doing work did not laying the foundation of hydrodynamics. Although (©2007 Jupiterimages and its licensors. Three items that are very essential to the exis- appear until after the decline of the Roman Empire. his name is applied to the Bernoulli theorem, some All rights reserved.) tence and comfort of humankind are associated The earliest record of a windmill-like device is from historians contend that his 1738 publication Hydro- with fluid power developments: central Asia. These wind-driven devices were used dynamics does not include specific formulas. He to turn prayer wheels. Historians believe that the ■ Transportation. extensively studied both static and dynamic fluid first “real” windmills were developed and used in phenomena. His contemporaries and successors Maudslay went on to develop numerous devices ■ Movement of water. central Asia about 400 AD. considered his work to be the first specific prin- and is generally considered to be the father of the ■ Generation and transmission of power. ciples on fluid movement. machine-tool industry. These elements have had far-reaching effects on James Watt (1736–1819) was a productive Lord William Armstrong (1810–1900) devel- the development of our industrial society. inventor who is usually thought of with respect oped a hydraulic accumulator that made a major to the steam engine, Figure 1-13. His inventive contribution to the development of the early fluid Artwork from Egyptian tombs that date to genius went well beyond this device, however. He power industry. An accumulator stores excessive 2500 BC shows reed boats with bipod masts and impressed his contemporaries as the individual pressurized fluid from the pump until needed sails designed for the special problems associ- who provided mankind with devices that had during peak system operation. The Armstrong ated with river sailing. Sails for the propulsion the potential of producing unlimited power. As accumulator was basically a large, vertically of ships continued to be refined through the ages. new designs were developed to meet the power positioned cylinder with a weighted ram. These Many sailing principles were applied to the devel- demands of the Industrial Revolution, Watt devel- devices were extensively used during the late opment of windmills and, eventually, pneumatic oped, or caused to be developed, new manufac- nineteenth century in large, centralized, pressur- components. turing techniques that greatly influenced the ized-fluid systems found in major cities through- Movement and control of water for irrigation, Industrial Revolution. out Great Britain. flood control, and municipal water systems also English engineer Joseph Bramah (1748–1814), Osborne Reynolds (1842–1912) established by produced ideas that eventually were used in fluid with his assistant Henry Maudslay (1771–1831), direct observation that two types of fluid flow power systems. Controlling the annual flood of the invented the cup seal. This seal greatly contributed exist: laminar (smooth and steady) and turbulent Nile River and moving water for irrigation pur- to the practical application of fluid power devices. (chaotic and rough). The observations he made poses during the remainder of the year produced Figure 1-14. An understanding of basic scientifi c The cup seal enabled the development of devices in 1883 eventually led to the development of a a better understanding of water flow in channels. principles has developed slowly throughout civiliza- requiring pressurized liquids and gases to oper- formula that produces a dimensionless number Archimedes is credited with inventing pumping tion. Ruins of the aqueduct system of the Roman ate with little leakage. Bramah went on to build today called the Reynolds number. The Reynolds devices that were used in the Nile Delta for irri- Empire illustrate an early need for a practical under- the first functional hydraulic press, which had number is considered one of the basic parameters gation purposes. Applications for moving and standing of fl uid fl ow. (©2007 Jupiterimages and its extensive application in the fluid power industry. of fluid mechanics. pumping water were also developed in the Islamic licensors. All rights reserved.) 26 Fluid Power Chapter 1 Introduction to Fluid Power 27

Middle Ages Many mechanical improvements were made During the Middle Ages following the fall of as water and windmills became prime sources of the Roman Empire, the development of new tech- power. These improvements included methods nology was extremely slow in Western civiliza- of power transmission through shafts, cogged tion. In the Western countries of Europe, existing wheels, crude gears, and cams. These devices were Roman structures were allowed to gradually dete- needed to transmit the power and transform it into riorate as major emphasis was placed on defense, the type of motion needed to do the desired work. conquest, development of monastic (religious) Many ingenious devices were developed that have orders, and support of the Crusades. The Islamic contributed to the body of knowledge as the world world, however, continued to make progress on moved toward the Industrial Revolution. public water supply systems, public baths, and power-driven mills. Many of these ideas were Industrial Revolution introduced in Europe during the twelfth and thir- The eighteenth and nineteenth centuries are teenth centuries by returning Crusaders. often designated as the period in which an “indus- At first, waterwheels were just a means of turn- trial revolution” occurred. That period of history ing millstones for grinding grain for local con- produced tremendous changes in world society, sumption. Waterwheels began to be recognized particularly in Great Britain. Great Britain had Figure 1-17. The steam engine provided a reliable, as an important source of power for other uses established extensive world trade, a strong finan- portable source of power. Its development is con- during the fourth and fifth centuries. They were Figure 1-15. Thousands of watermills have been cial base, large local reserves of iron ore and coal, sidered one of the key factors in the development of slowly adapted for use in sawmills, paper mills, © used throughout history as prime movers for and key individuals interested in the practical the Industrial Revolution. ( 2007 Jupiterimages and iron mills, and mining operations. An example grinding grain and powering early machines. development of scientific principles. These factors its licensors. All rights reserved.) of the slow, but pervasive, growth of water power Modern water turbines for electric generation combined to lead to the Industrial Revolution. as a prime mover is that the earliest recorded use and ﬂ uid power motors have evolved from these Changes during the Industrial Revolution in England was in the eighth century with over early designs. (©2007 Jupiterimages and its occurred much more quickly than those during 5000 in use by the eleventh century, Figure 1-15. licensors. All rights reserved.) the Middle Ages. However, identification of spe- developed to satisfy these needs are where fluid Water mills were profitable operations and found cific dates or events that started the “revolution” is power, as we think of it today, began to emerge. in every community that had a suitable stream. not possible. It must also be emphasized that the Many of the early fluid power elements involved Windmills continued to be developed in several industrial change was not just tied to mechani- pumping water from mines or for manufacturing forms in the Near East, where easy access to water cal devices, but involved changes as diverse as uses. James Watt designed steam-driven, recipro- was limited. Records indicate that windmills were world trade and application of scientific methods. cating pumps that were used in the late 1700s and extensively used in Afghanistan and Persia, with Nevertheless, development of new prime movers early 1800s. By the mid-1800s, these pumps were a number of designs developed to control speed. must be considered to be the key to the Industrial widely used. The East London Water Company Speed control was required because of strong winds Revolution, Figure 1-17. The steam engine, inter- operated a unit with a 100″ diameter cylinder and in the area. Use of wind power spread throughout nal combustion engine, and gas turbine all were a stroke of 11 feet. By the 1870s, patents were issued the Islamic world during the period. developed during the period. Unlike water and for variable-stroke, piston pumps. The centrifugal The first recorded use of windmills in windmills, these devices were mobile and not pump was invented in the late 1600s, but was not Western Europe was during the twelfth century, dependent on local weather or terrain conditions. generally used until the mid-1800s. The jet pump Figure 1-16. These mills were initially used for Even with those new power development devices, was also produced during this same period. grinding grain, but were gradually modified for water and windmills continued to play important A key factor that allowed the development of use in other applications, such as sawing lumber, roles in industrial power generation throughout many practical fluid power components was the pumping water, and manufacturing. Holland and the middle 1800s and much later in smaller, local cup seal. This type of seal uses the pressure within the other “low countries” of Europe were prime and rural applications. the system to force a sealing collar against a shaft users of these mills because of their flat terrain The use of machines instead of hand tools was or ram to prevent fluid loss, Figure 1-18. Invented and consistent winds. another key to the changes of the period. These in 1795, the cup seal allowed hydraulic presses to Windmills gradually developed with improve- machines exceeded the capabilities of skilled be built that both did not leak and could be con- ments in design and increases in size. Power out- craftsmen to develop products. They allowed pro- tinuously used. put ranged from 4 to 5 horsepower for the average Figure 1-16. Windmills have played an important duction rates that met demands resulting from Two other devices that were especially impor- mill to over 15 horsepower for larger mills. At the part in the development of civilization. Their use expanded trade areas. tant to the development of fluid power during the peak of windmill use, Holland had over 8000 mills, was limited to areas with consistent winds, such as The development of manufacturing increased 1800s were the hydraulic accumulator and the with many of them having sail spans as large as coastal and plains areas. (©2007 Jupiterimages and the need for methods and devices to move water hydraulic intensifier. Large, weighted accumula- 100 feet. its licensors. All rights reserved.) and transmit power. The procedures and devices tors were used to store pressurized fluid from 28 Fluid Power Chapter 1 Introduction to Fluid Power 29

Fluid power development and use during the nineteenth century was very extensive. This use involved the generation of power through the design of effective water turbines; the transmission of power using central power stations and elaborate distribution lines; and the use of fluid power in construction, manufacturing, and material distribution systems.

Recent history The emphasis on the development of fluid power applications decreased as the use of electric- ity grew in the late 1800s and early 1900s. Devel- opment concentrated more in the heavy industrial and mobile areas where fluid power applications appeared to be most practical. Generally, these factors have promoted progress in fluid power applications in recent years: ■ Figure 1-18. Modern sealing devices are often taken Development of new materials. for granted. However, their development in the late ■ Miniaturization of components. Figure 1-19. Compact power sources such as these hydraulic units have added fl exibility to the application of fl uid power. (Continental Hydraulics) 1700s by Bramah and Maudslay was instrumental ■ Effective electrical/electronic control. to the practical application of fl uid power principles. (Photo courtesy of Apple Rubber Products, Inc.) Improvements were made in sealing devices and machining techniques that reduced both internal and external leaks. This, in turn, improved It has been the key to the development of today’s system efficiency. Reducing external leaks also large mobile hydraulics field. a pump during the idle time of a press or other allowed use in applications where cleanliness was The development of new materials and manu- machine. During peak operating time the charged an important factor. Water was replaced in hydrau- facturing techniques has promoted the design of accumulator assisted the pump by supplying high lic systems by petroleum-based fluids, which new fluid power concepts and allowed practical volumes of fluid needed for operation. improved lubrication and eliminated the danger application of old ideas, Figure 1-20. The miniatur- The hydraulic intensifier was used to more of freezing in cold climates. ization of components has produced new applica- easily obtain high system pressures for use in bail- Military applications contributed to the devel- tions, while the combining of electrical/electronic ing, metal forming, forging, or other applications. opment of fluid power. A milestone occurred in control and fluid power systems has produced The intensifier, which usually consisted of some 1906 when hydraulic systems first appeared on more effective machines. Two components that combination of large and small diameter rams, a warship, the battleship USS Virginia. These illustrate these factors are hydrostatic transmis- used the area differences of the rams to boost sys- hydraulic systems replaced many mechanical and sions and servo systems. These units are heavily tem pressure above the capability of the pump. electrical systems. Since that time, all branches used in both industrial and consumer applica- This principle allowed the use of higher pressure of the military have incorporated fluid power tions, Figure 1-21. Neither could exist in their pres- even when the technology of the time did not allow on numerous devices to solve problems in gun- ent form without the sophistication of the present pumps to operate at extremely high pressure. nery, materials handling, navigation, and support manufacturing community. Pressurized water was extensively used to dis- services. Today’s automobile can be used as an example tribute power to businesses and manufacturers The development and refinement of the con- of the use of fluid power. The body of the vehicle in several cities in Great Britain. By 1900, it was cept of compact hydraulic units in the 1920s had is formed by huge hydraulic-powered presses. considered economical to transmit power up to a far-reaching effect, extending to today’s fluid Hydraulically-controlled resistance welding equip- 15 miles from a centralized pumping station. These power applications, Figure 1-19. These self-con- ment assembles those parts, while untold numbers systems provided water under several hundred tained systems include the power source, pump, of other hydraulic and pneumatic tools are used in pounds per square inch of pressure that could be and reservoir. The units have been applied to a the production of the additional parts and during directly used for the operation of presses, hoists, full range of industrial and consumer applications. the final assembly process. Intricate fluid power Figure 1-20. Central power systems are often used and water motors. These systems continued in use Central hydraulic and pneumatic power systems systems are also used in the steering, braking, and in large manufacturing facilities to produce com- until electrical generating and distribution sys- have remained in large industrial applications, but ride control systems of the vehicle, which promote pressed air for pneumatic applications. tems were perfected. the more-compact direct system adds flexibility. safety and comfort of the driver and passengers. (Photo: Atlas Copco) 30 Fluid Power Chapter 1 Introduction to Fluid Power 31

10. James Watt, who perfected the steam engine, 13. In early times, the movement and control of is credited with greatly influencing the Indus- water for ______, ______, and ______also pro- trial Revolution through his development of duced ideas that eventually were used in fluid new and innovative ______techniques. power systems. 11. ______and ______are credited with the inven- 14. The invention of new ______is usually consid- tion of the cup seal, which led to the develop- ered to be the key that allowed the development of the first functional hydraulics press. ment of the Industrial Revolution. 12. Artwork from Egyptian tombs indicates that 15. List three factors that have promoted progress sails were used to assist in the propulsion of in fluid power applications in recent years. boats as early as ______BC.

Figure 1-22. Windmills have experienced a resur- Figure 1-21. An automobile assembly line illustrates gence as prime movers in the windmill farms cur- the diverse use of ﬂ uid power in industry today. A rently used for electrical generation. As energy full range of both pneumatic and hydraulic applica- costs rise, so does interest in harvesting this “free” tions can be found in such operations. energy. (©2007 Jupiterimages and its licensors. All (Photo: Atlas Copco) rights reserved.)

To say the least, fluid power has grown tre- 5. The ______fluid power system can usually mendously during the 1900s and into the 2000s. provide the best solution where lightweight Current space technology, manufacturing indus- and easily handled tools are a requirement. try demand, and consumer interest indicate that 6. The pneumatic fluid power system is gener- this growth will continue into the twenty-first ally considered to be the most expensive to century, Figure 1-22. operate because of the cost of ______, ______, and ______the air. 7. Clean operation with minimum fire haz- Chapter Test ards are characteristics of which fluid power system(s)? Answer the following questions. Write your answers on a separate sheet of paper. 8. The earliest records indicating the use of natural air and water movement to reduce 1. Fluid power systems use ______fluids to effort comes from archaeological discoveries transmit power. in ______. 2. The physical components in a fluid power A. Egypt system are used to ______, ______, and ______power to produce the desired results in an B. Germany application. C. Holland 3. The three power transfer systems commonly D. Great Britain used today are ______, ______, and ______. 9. It is generally believed by historians that 4. Name six industries in which fluid power much of the early development of fluid power applications contribute to daily operations was based on ______, rather than on an and long term business success. understanding of scientific principles.