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1、1 / 10 Hydraulic systemand Peumatic System Hui-xiongwan1,Jun Fan2Abstract:Hydraulic system is widely used in industry, such as stamping, grinding of steel type work and general processing industries, agriculture, mining, space technology, deep sea exploration, transportation, marine technology, offs
2、hore gas and oil exploration industries, in short, Few people in their daily lives do not get certain benefits from the hydraulic technology. Successful and widely used in the hydraulic systems secret lies in its versatility and ease of maneuverability. Hydraulic power transmission mechanical system
3、s as being not like the machine geometry constraints, In addition, the hydraulic system does not like the electrical system, as constrained by the physical properties of materials, it passed almost no amount of power constraints. Keywords: Hydraulic system,Pressure system,FluidThe history of hydraul
4、ic power is a long one, dating from man s prehistoric efforts to harness the energy in the world around him. The only source readily available were the water and the wind two free and moving streams. The watermill, the first hydraulic motor, was an early invention. One is pictured on a mosatic at th
5、e Great Palace in Byzantium, dating from the early fifth century. The mill had been built by the Romans. But the first record of a watermill goes back even further, to around 100BC, and the origins may indeed have been much earlier. The domestication of grain began some 5000 years before and some en
6、terprising farmer is bound to have become tired of pounding or grinding the grain by hand. Perhaps, in fact, the inventor were some farmers wives. Since the often drew the heavy jobs.Fluid is a substance which may flow 。 that is, its constituent particles may continuously change their positions rela
7、tive to one another. Moreover, it offers no lasting resistance to the displacement, however great, of one layer over another. This means that, if the fluid is at rest, no shear force (that is a force tangential to the surface on which it acts) can exist in it. Fluid may be classified as Newtonian or
8、 non-Newtonian. In Newtonian fluid there is a linear relation between the magnitude of applied shear stresses and the resulting rate of angular deformation. In nonNewtonian fluid there is a nonlinear relation between the magnitude of applied shear stress and the rate of angular 精选学习资料 - - - - - - -
9、- - 名师归纳总结 - - - - - - -第 1 页，共 10 页2 / 10 deformation. The flow of fluids may be classified in many ways, such as steady or non steady, rotational or irrotational, compressible or incompressible, and viscous or no viscous. All hydraulic systems depend on Pascals law, such as steady or pipeexerts eq
10、ual force on all of the surfaces of the container. In actual hydraulic systems, Pascals law defines the basis of results which are obtained from the system. Thus, a pump moves the liquid in the system. The intake of the pump is connected to a liquid source, usually called the tank or reservoir. Atmo
11、spheric pressure, pressing on the liquid in the reservoir, forces the liquid into the pump. When the pump operates, it forces liquid from the tank into the discharge pipe at a suitable pressure. The flow of the pressurized liquid discharged by the pump is controlled by valves. Three control function
12、s are used in most hydraulic systems: (1) control of the liquid pressure, （2）control of the liquid flow rate, and (3) control of the direction of flow of the liquid. Hydraulic drives are used in preference to mechanical systems when(1) powers is to be transmitted between point too far apart for chai
13、ns or belts 。 (2) high torque at low speed in required。(3) a very compact unit is needed。(4) a smooth transmission, free of vibration, is required。(5) easy control of speed and direction is necessary 。 and (6) output speed is varied steplessly. Fig. 1 gives a diagrammatic presentation of the compone
14、nts of a hydraulic installation. Electrically driven oil pressure pumps establish an oil flow for energy transmission, which is fed to hydraulic motors or hydraulic cylinders, converting it into mechanical energy. The control of the oil flow is by means of valves. The pressurized oil flow produces l
15、inear or rotary mechanical motion. The kinetic energy of the oil flow is comparatively low, and therefore the term hydrostatic driver is sometimes used. There is little constructional difference between hydraulic motors and pumps. Any pump may be used as a motor. The quantity of oil flowing at any g
16、iven time may be varied by means of regulating valves( as shown in Fig.7.1) or the use of variable-delivery pumps. The application of hydraulic power to the operation of machine tools is by no means new, though its adoption on such a wide scale as exists at present is comparatively recent. It was in
17、 fact in development of the modern self-contained pump unit that stimulated the growth of this form of machine tool operation. 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 2 页，共 10 页3 / 10 Hydraulic machine tool drive offers a great many advantages. One of them is that it can give infinitely-varia
18、ble speed control over wide ranges. In addition, they can change the direction of drive as easily as they can vary the speed. As in many other types of machine, many complex mechanical linkages can be simplified or even wholly eliminated by the use of hydraulics. The flexibility and resilience of hy
19、draulic power is another great virtue of this form of drive. Apart from the smoothness of operation thus obtained, a great improvement is usually found in the surface finish on the work and the tool can make heavier cuts without detriment and will last considerably longer without regrinding. Hydraul
20、icandpneumaticsystem Thereare only three basic methods oftransmitting power:electrical,mechanical,and fluid power.Most applications actually use a combination of the three methods to obtain the most efficient overall system. To properly determine which principle method to use,it is important to know
21、 the salient features of each type. For example, fluid systems can transmit power more economically over greater distances than can mechanical types. However, fluid systems are restricted to shorter distances than are electrical systems. Hydraulic power transmission system are concerned with the gen
22、eration, modelation, and control of pressure and flow ，and in general such systems include: 1. Pumps which convert available power from the prime mover to hydraulic power at the actuator. 2. Valves which control the direction of pump-flow, the level of power produced, and the amount of fluid-flow to
23、 the actuators. The power level is determined by controlling both the flow and pressure level. 3. Actcators which convert hydtaulic power to usable mechanical power output at the point required. 4. The medium, which is a liquid, provides rigid transmission and control as well as lubrication of compo
24、nts, sealing in valves, and cooling of the system. 5. Conncetots which link the various system components, provide power conductors for the fluid under pressure, and fluid flow return to tank(reservoir). 6. Fluid storage and conditioning equipment which ensure sufficient quality and quantity as well
25、 as cooling of the fluid. Hydraulic systems are used in industrial applications such as stamping presses, steel mills, and general manufacturing, agricultural machines, mining industry, 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 3 页，共 10 页4 / 10 aviation, space technology, deep-sea exploration,
26、transportion, marine technology, and offshore gas and petroleum exploration. In short, very few people get through a day of their lives without somehow benefiting from the technology of hydraulicks. The secret of hydraulic systems success and widespread use is its versatility and manageability. Flui
27、d power is not hindered by the geometry of the machine as is the case in mechanical systems. Also, power can be transmitted in almost limitless quantities because fluid systems are not so limited by the physical limitations of materials as are the electrical systems. For example, the performance of
28、an electromangnet is limited by the saturation limit of steel. On the other hand, the power limit of fluid systems is limited only by the strength capacity of the material. Industry is going to depend more and more on automation in order to increase productivity. This includes remote and direct cont
29、rol of production operations, manufacturing processes, and materials handling. Fluid power is the muscle of automation because of advantages in the following four major categories. 1. Ease and accuracy of control. By the use of simple levers and push buttons, the operator of a fluid power system can
30、 readily start, stop, speed up or slow down, and position forces which provide any desired horsepower with tolerances as precise as one ten-thousandth of an inch. 2. Multiplication of force. A fluid power system(without using cumbersome gears, pulleys, and levers) can multiply forces simply and effi
31、ciently from a fraction of an ounce to several hundred tons of output. 3. Constant force or torque. Only fluid power systems are capable of providing contant force or torque regardless of speed changes. This is accomplished whether the work output moves a few inches per hour, several hundred inches
32、per minute, a few revolutions per hour, or thousands of revolutions per minute. 4. Simplicity, safely, economy. In general, fluid power systems use fewer moving parts than comparable mechanical or electrical systems. Thus, they are simpler to maintain and operate. This, in turn, maximizes safety, co
33、mpanctness, and reliability. For example, a new power steering control designed has made all other kinds of power systems obsolete on many off-highway vehicles. The steering unit consists of a manually operated directional control valve and meter in a single body. Because the steering unit is fully
34、fluid-linked, mechanical linkages, universal joints, bearings, reduction gears, etc, are eliminated. This provides a simple, compact system. In addition, very little input torque is required to produce the control needed for the 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 4 页，共 10 页5 / 10 toughes
35、t applications. This is important where limitations of control space require a small steering wheel and it becomes necessary to reduce operatotr fatique. Additonal benefits of fluid power systems include instantly reversible motion, automatic protection against overloads, and infinitely variable spe
36、ed control. Fluid power systems also have the highest horsepower per weight ratio of any known power source. In spite of all these highly desirable features of fluid power, it is not a panacea for all power transmission problems. Hydraulic systems also have some drawbacks. Hydraulic oils are messy,
37、and leakage is impossible to completely eliminate. Also, most hydraulic oils can cause fires if an oils occurs in an area of hot equipment. Peumatic System Pneumatic systems use pressurized gases to tansmit and control power. A s the name implies, pneumatic systems typically use air(rather than some
38、 other gas) as the fluid medium because air is a safe, low-cost, and readily available fluid. It is particularly safe in environments where an electrical spark could ignite leaks from system components. In pneumatic systems ,compressors are used to compress and supply the necessary quantities of air
39、. Compressors are typically of the piston, vane or screw type. Basically a compressor increases the pressure of a gas by reducing its volume as described by the perfect gas laws.Pneumatic systems normally use a large centralized air compressor which is considered to be an infinite air source similar
40、 to an electrical system where you merely plug into an electrical outlut for electricity. In this way, pressurized air can be piped from one source to various locations throughout an entire industrial plant. The air then flows through a pressue regulator which redeces the pressure to the desired lev
41、el for the particular circuit application. Because air is not a good lubircant（ contains about 20% oxygen） , pneumatics systems required a lubricator to inject a very fine mist of oil into the air discharging from the pressure regulator. This prevents wear of the closely fitting moving parts of pneu
42、matic components. Free air from the atmosphere contains varying amounts of moisure. This moisure can be harmful in that it can wash away lubricants and thus cause excessive wear and corrosion. Hence ,in some applications ,air driers are needed to remove this undesirable moisture. Since pneumatics sy
43、stems exhaust directly into the atmosphere, they are capable of generating excessive noise. Therefore, mufflers are mounted on exhaust ports of air valves and actuators to reduce noise and prevent operating 精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 5 页，共 10 页6 / 10 personnel from injury resulti
44、ng not only from exposure to noise but also from high-speed airborne particles. There are several reasons for considering the use of pneumatic systems instead of hydraulic systems. Liquids exhibit greater inertia than do gases. Therefore, in hydraulic systems the weight of oil is a potential problem
45、 when accelerating and decelerating actuators and when suddenly opening and closing valves. Due to Newtons law of motion(force equals mass multiplied by acceleration), the force required to accelerate oil is many times greater than that required to accelerate an equal volume of air. Liquids also exh
46、ibit greater viscosity than do gases. This results in larger frictional pressure and power losses. Also ,since hydraulic systems use a fluid foreign to the atmosphere, they require special reservoirs and noleak system designs. Pneumatic system use air which is exhausted directly back into the surrou
47、nding environment. Generally speaking, pneumatic systems are less expensive than hydraulic systems. However, because of the compressibility of air, it is impossible to obtain precise controlled actuator velocities with pneumatic systems. Also, precise positioning control is not obtainable. While pne
48、umatics pressures are quite low due to compressor design limitations(less than 250 psi), hydraulic pressures can be as high as 10000 psi. Thus, hydraulics can be high-power systems, whereas pneumatics are confined to low-power applications. Industrial applications of pneumatics systems are growing a
49、t a rapid pace. Typical examples include stamping, drilling, hoist, punching, clamping, assembling, riveting, materials handling, and logic controlling operations. 液压系统和气压系统万辉雄1，范军2摘要：液压系统在工业中应用广泛，例如冲压、钢类工件的磨削及一般加工业、农业、矿业、航天技术、深海勘探、运输、海洋技术，近海天然气和石油勘探等行业，简而言之，在日常生活中很少有人不从液压技术得到某些益处。液压系统成功而又广泛使用的秘密在于它
50、的通用性和易操作性。液压动力传递不会像机械系统那样受到机器几何形体的制约，另外，液压系统不会像电精选学习资料 - - - - - - - - - 名师归纳总结 - - - - - - -第 6 页，共 10 页7 / 10 气系统那样受到材料物理性能的制约，它对传递功率几乎没有量的限制。关键词：液压系统，气压系统，流体流体和液压系统水力的历史由来已久，始于人类为利用它周围的能源而做出的努力。容易利用的能源就是水和风两种自由的流动流体。第一台液力装置水车是最早的发明。从15 世纪早期，水车图画就出现在大宫殿的马赛克上。磨粉机由罗马人发明，而水磨机的历史更早，可以追溯到大约公元前100 年。当一些