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1、unit 24 Hydraulic and pneumatic SystemsTuning in Task 1 Can you explain the two words: hydraulic and pneumatic in English? Do you know any hydraulic or pneumatic systems？ Task 2 Read the text and answer these quentions: (1) Whats the basic idea behind any hydraulic systems? (1) The basic idea behind
2、 any hydraulic system is very simple: Force that is applied at one point is transmitted to another point using an incompressible fluid. (2) How is a force multiplied in a hydraulic system? (2) If the areas of the two pistons in the system are different, one is bigger and the other is small. (3) List
3、 major components of a log splitter. (3) The major components of the log splitter are: hydraulic cylinder, valve, pump, engine and handle. (4) How is the piston in the log splitter pushed into and drawn back out of the log? (4) When you apply a force on the smaller piston, you will get multiplied fo
4、rce on the bigger piston. Text Hydraulic Systems Maybe hydraulic is a tough word for you, but the basic idea behind any hydraulic system is very simple: Force that is applied at one point can be transmitted to another point by an incompressible fluid. The fluid is almost always an oil of some sort.
5、The force is almost always multiplied in the process. Figure 24-1 shows the simplest possible hydraulic systems:Figure 24-1 A simple hydraulic system consisting of two pistons and an oil-filled pipe connecting them In Figuer 24-1, there are two cylinders filled with oil. In each one of them, there i
6、s a piston fit in it. At the bottom of the two cylinders, they are connected together by an oil-filled pipe. If you apply a downward force to one piston, the force will be transmitted to the second piston through the oil in the pipe. Since oil is incompressible, the efficiency is very goodalmost all
7、 of the applied force appears at the second piston. One of the advantages of hydraulic systems is that it is very easy to add force multiplication (or division) to the system. All you have to do is changing the size of one piston and cylinder relative to the other, as shown in Figure 24-2:Figure 24-
8、2 Hydraulic multiplication The piston on the right has a surface area nine times greater than the piston on the left. When force is applied to the left piston, it will move nine units for every one unit that the right piston moves, and the force is multiplied by nine on the right-hand piston. Lets s
9、ee how hydraulic systems work for us. The simplest hydraulic device that you find in common use is the log splitter. It contains all of the basic components of a hydraulic machine(see Figure 24-3):Figure 24-3 The major components of a log splitter (1) An engine, normally a small four-stroke gasoline
10、 engine, provides the power for the system. The engine is attached to a hydraulic oil pump. (2) The hydraulic oil pump creates a stream of high-pressure oil, which runs to a value. (3) The value lets the operator actuate the hydraulic cylinder to split a log. There is also a tank to hold the hydraul
11、ic oil that feeds the pump and usually a filter to keep the oil clean. The major components of a log splitter are shown below: In Figure 24-4 you can see how the valve can apply both forward and backward pressures to the piston. When you push the handle, the high-pressure oil will be pumbed into the
12、 left side of the piston(see Figure b), pushing the piston forward and driving the machine to split the log. When you pull the handle, the high-pressure oil will be pumped into the right side of the piston(see Figure a), drawing the piston back out of a log.Figure 24-4 Two important positions of the
13、 splitter in cross section (High-pressure oil from the pump is shown in blue, and low-pressure oil returning to the tank is shown in grey.) Language study Allow and prevent links Task 3 Figure 24-5 shows the most basic componets of a pneumatic system, a three-port valve(3PV) and a single acting cyli
14、nder(SAC). The steps below describe the operation of the system when the push button of the valve is pressed. The first step is A.Put the others in the correct sequence.Figure 24-5 A three-port valve and a single acting cylinder(button is pressed) A. The push button is pressed. (1) B. Port 3 is bloc
15、ked (5) C. ports 1 and 2 are connected. (3) D. The piston compresses the spring. (8) E. The spool is pushed down (2) F. Air cannot escape. (6) G. Compressed air flows through the valve to the SAC (4) H. The compressed air pushes the piston along. (7) Study these steps from the operation of the valve. (1) Ports 1 and 2 are connected. (2) Compressed air flows through the valve to the SAC.
