飛機(jī)液壓系統(tǒng)活門介紹PPT課件

1、.,1,Basic Aircraft system Valves of Aircraft Hydraulic System,.,2,Basic Aircraft Systemshydraulic system,HYDRAULIC SYSTEM VALVES The valves used in hydraulic systems may be divided into: Flow-control valves. A flow-control valve selects the route of flow of the fluid through the system, and is not n

2、ormally concerned with the pressure. Pressure-control valves On the other hand, pressure-control valves adjust, regulate, or limit the amount of pressure in the system, or in any portion of the system.,.,3,Basic Aircraft Systemshydraulic system,HYDRAULIC SYSTEM VALVES FLOW CONTROL VALVES For hydraul

3、ic components and systems to operate as intended, the flow of fluid must be rigidly controlled. Fluid must be made to flow according to definite plans. Many kinds of valve units are used for exercising such control. 1. selector valves (選擇活門) 2. check valves (單向活門) 3. sequence valves (順序活門) 4. priori

4、ty valves (優(yōu)先活門) 5. quick disconnect valve (快斷活門) 6. hydraulic fuses (液壓保險(xiǎn)),.,4,.,5,Basic Aircraft Systemshydraulic system,VALVES-SELECTOR VALVES Selector Valves One of the most familiar flow-control valves is the selector valve, which determines the direction of flow of fluid to retract or extend t

5、he landing gear, or to select the position of the wing flaps. Two commonly used types of selector valves:,.,6,Basic Aircraft Systemshydraulic system,VALVES-SELECTOR VALVES Selector Valves Open-center valve The open-center valve directs fluid through the center of the valve back to the reservoir when

6、 a unit is not being actuated. Closed-center valve The closed-center valve stops the flow of fluid when it is in its neutral position. Both valves direct fluid from the pump to one side of the actuator and vent the opposite side to the reservoir.,.,7,Basic Aircraft Systemshydraulic system,VALVES-SEL

7、ECTOR VALVES Open-center valve The open-center valve is an open-center poppet-type selector valve utilized in an open-center hydraulic system (refer back to Figure 8-17). When the selector handle is in the neutral position, the appropriate poppet is off of its seat. Fluid flows straight through the

8、valve from the pump to the next selector valve and on to the reservoir. Figure 8-37, view (A),.,8,.,9,Basic Aircraft Systemshydraulic system,VALVES-SELECTOR VALVES Open-center valve When the actuator reaches the end of its travel, the pump continues to produce a flow of fluid. A system relief valve

9、(refer back to Figure 8-17) must off-seat to allow a flow back to the reservoir until the selector valve is moved to its neutral position. Some open-center valves have an automatic feature that causes them to move to the neutral position when the pressure rises to a specified value.,.,10,Basic Aircr

10、aft Systemshydraulic system,VALVES-SELECTOR VALVES Open-center valve When the actuator reaches the end of its travel, the pump continues to produce a flow of fluid. A system relief valve (refer back to Figure 8-17) must off-seat to allow a flow back to the reservoir until the selector valve is moved

11、 to its neutral position. Some open-center valves have an automatic feature that causes them to move to the neutral position when the pressure rises to a specified value.,.,11,Basic Aircraft Systemshydraulic system,VALVES-SELECTOR VALVES Open-center valve When the gear selector is moved to the GEAR

12、UP position, poppets 2 and 5 open, and fluid from the pump flows around poppet 2, while the return fluid flows around poppet 5 as in Figure 8-37, view (C).,.,12,Basic Aircraft Systemshydraulic system,VALVES-SELECTOR VALVES Closed-center valve 1. Plug-type closed-center valves are often used in aircr

13、aft hydraulic systems. In one position, the pressure port and one actuator port are connected, while the other actuator port is connected to the return port. Rotating the selector handle ninety degrees reverses the connection between the actuator ports and the pressure and return lines. Figure 8-38,

14、.,13,.,14,Basic Aircraft Systemshydraulic system,Poppet Valve A poppet valve (also called mushroom valve) is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding thro

15、ugh a valve guide. In most applications a pressure differential helps to seal the valve and in some applications also open it.,.,15,.,16,Basic Aircraft Systemshydraulic system,VALVES-SELECTOR VALVES Closed-center valve 2. poppet-type selector valve (提升閥,菌形活門) A more positive shutoff of fluid may be

16、provided by using a poppet-type selector valve, such as the one shown in Figure 8-39. In the GEAR UP position (view A), poppets 2 and 3 are off of their seats, and poppets 1 and 4 are seated. Fluid flows from the pump around poppet one to one side of the actuator piston and raises the landing gear.

17、The fluid from the opposite side of the actuator piston is pushed out of the cylinder, around poppet three, and back to the reservoir.,.,17,.,18,Basic Aircraft Systemshydraulic system,VALVES-SELECTOR VALVES Closed-center valve 2. poppet-type selector valve When the gear selector handle is placed in

18、the GEAR DOWN position (view B), poppets 1 and 4 are off-seated, and poppets 2 and 3 are seated. Fluid flows from the pump around poppet 1 into the actuator, while the displaced fluid flows around poppet 4 back into the reservoir.,.,19,Basic Aircraft Systemshydraulic system,VALVES-SELECTOR VALVES Cl

19、osed-center valve： 2. poppet-type selector valve In a closed-center hydraulic system, the selector valve may shut off the flow of fluid without causing any rise in the system pressure. Reason: This is because the system uses a pressure regulator to maintain the system pressure independent of the pos

20、ition of any selector valve.,.,20,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES Check Valves There are many instances in an aircraft hydraulic system where it is desirable to allow fluid to flow in one direction but prevent its flow in the opposite direction. This is done with check val

21、ves.,.,21,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES Types of Check Valves 1.Flap type - this type of check valve is not used in hydraulics,.,22,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES Types of Check Valves 2. Ball Type Too heavy and has too much inertia to move,.,

22、23,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES Types of Check Valves 3. Poppet type valve is the preferred type that is used in hydraulics now.,.,24,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES 3. Poppet type valve is the preferred type that is used in hydraulics now. Th

23、e front of the poppet (left side of the picture above) sits snugly on the hard seat (darker shaded areas on the left side). The poppet works on the following principle. When high pressure fluid (with pressure P1 ) comes in on the left, it forces the poppet open.,.,25,Basic Aircraft Systemshydraulic

24、system,VALVES-CHECK VALVES 3. Poppet type valve is the preferred type that is used in hydraulics now. Since P1P2 , the force on the left side of the poppet (F1) is greater than the force due to the spring (F2 ) and is just enough to open the poppet. But, when flow stops, or there is a high pressure

25、flow from the right side of the poppet, then P2P1 and the pressure forces the poppet against the valve seat, closing off the opening. Thus the fluid is allowed to flow through in one direction only.,.,26,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES Check valves are designed so as not t

26、o tolerate leakage. The purpose of the light spring is only to keep the poppet on the seat. Most manufacturers use sharp-edged, very hard seats and soft, maybe plastic, poppets. Parallel seats are very good except that they are too prone to trapping contaminants between the seat and the poppet.,.,27

27、,.,28,.,29,.,30,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES Check valves are made in two general designs to serve two different needs. In one, the check valve is complete within itself. It is interconnected with other components by means of tubing or hose. Check valves of this design

28、are commonly called inline check valves. In the other design, the check valve is not complete within itself because it does not have a housing exclusively its own. Check valves of this design are commonly called integral check valves. This valve is actually an integral part of some major component a

29、nd, as such, shares the housing of that component.,.,31,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES There are several types of in-line check valves in use. The ball-type valve is perhaps the most familiar. It allows fluid to flow in one direction, but it cannot flow in the opposite di

30、rection. Figure 8-40, view (A) The cone-type check valve, Figure 8-40, view (B), behaves in much the same way except that the seal is provided by a cone rather than by a ball.,.,32,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES Neither of these check valves allows an entirely free flow i

31、n the direction of the arrow since the flow is opposed by the spring that holds the valve seated. A valve of this type is used to maintain case pressure in a gear-type hydraulic pump. The spring force determines the pressure needed to open the check valve.,.,33,Basic Aircraft Systemshydraulic system

32、,VALVES-CHECK VALVES Swing-type valve（回轉(zhuǎn)閥） Some applications for a check valve cannot tolerate the opposition to the flow of fluid, and if this is the case, a swing-type valve may be used, as in Figure 8-40, view (C). CONFIGURATION A disk is held with a very weak spring over the opening to the passa

33、ge inside the check valve. Fluid flowing in the direction of the arrow can easily force the valve open and flow through with almost no opposition. But, fluid attempting to flow in the opposite direction will force the disc over the opening and prevent any flow.,.,34,Basic Aircraft Systemshydraulic s

34、ystem,ORIFICE CHECK VALVES Certain applications require full flow of fluid in one direction and restricted flow in the opposite direction. An example of this is in a landing-gear system where air loads and the weight of the gear cause the extension to be excessively fast. The weight of the gear agai

35、nst the air load requires every bit of pressure possible to get the gear up. Figure 8-41,.,35,Basic Aircraft Systemshydraulic system,ORIFICE CHECK VALVES An orifice check valve is an example of an integral check valve and is installed in such a way that fluid flowing through the gear-up lines is not

36、 restricted, While fluid leaving the gear-up side of the actuator is restricted by the orifice in the check valve. Figure 8-41,.,36,.,37,Basic Aircraft Systemshydraulic system,VALVES-SEQUENCE VALVES Modern aircraft with retractable landing gear often have doors that close in flight to cover the whee

37、l well and make the airplane more streamlined. To be sure the landing gear does not extend before the doors are opened, sequence valves may be used. These are actually check valves which allow a flow in only one direction, but may be opened manually to allow fluid to flow in either direction. Figure

38、 8-42,.,38,.,39,Basic Aircraft Systemshydraulic system,VALVES - SEQUENCE VALVES In a landing gear system, the wheel well doors must be fully open before the landing gear is extended. In this system, the gear door actuating piston opens the sequence valve when the doors are fully open, allowing fluid

39、 to flow into the main landing gear cylinder. The return fluid flows unrestricted through the sequence valve on its way back into the reservoir. Figure 8-43,.,40,.,41,Basic Aircraft Systemshydraulic system,VALVES-PRIORITY VALVES Priority Valves Priority valves are similar to sequence valves, except

40、that they are opened by hydraulic pressure rather than by mechanical contact. They are called priority valves because such devices as wheel well doors, which must operate first, require a lower pressure than the main landing gear, and the valve will shut off all the flow to the main gear until the d

41、oors have actuated and the pressure builds up at the end of the actuator stroke. When this buildup occurs, the priority valve opens so fluid can flow to the main gear. Figure 8-44,.,42,.,43,Basic Aircraft Systemshydraulic system,QUICK DISCONNECT VALVES Quick-Disconnect Valves Quick-disconnect, or li

42、ne-disconnect valves, are installed in hydraulic lines to prevent the loss of fluid when units are removed. Such valves may be installed in the pressure and suction lines of the system just in front, and immediately behind the power pump.,.,44,Basic Aircraft Systemshydraulic system,QUICK DISCONNECT

43、VALVES These valves can also be used in ways other than just for unit replacement. A power pump can be disconnected from the system and a hydraulic test stand connected in its place. CONFIGURATION Quick disconnect valve units consist of two interconnecting sections coupled by a nut when installed in

44、 the system. Each valve section has a piston and poppet assembly. These are spring loaded to the CLOSED position when the unit is disconnected. Figure 8-45,.,45,.,46,Basic Aircraft Systemshydraulic system,QUICK DISCONNECT VALVES The top illustration of Figure 8-45 shows the valve in the LINE-DISCONN

45、ECTED position. The two springs (a and b) hold both poppets (c and f) in the CLOSED position as shown. This prevents loss of fluid through the disconnected line. The bottom illustration of Figure 8-45 shows the valve in the LINE-CONNECTED position. When the valve is being connected, the coupling nut

46、 draws the two sections together.,.,47,Basic Aircraft Systemshydraulic system,QUICK DISCONNECT VALVES The extension (d or e) on one of the pistons forces the opposite piston back against its spring. This action moves the poppet off its seat and permits fluid to flow through that section of the valve

47、. As the nut is drawn up tighter, one piston hits a stop; then the other piston moves back against its spring and, in turn, allows fluid to flow. Thus, fluid is allowed to continue through the valve and on through the system.,.,48,Basic Aircraft Systemshydraulic system,QUICK DISCONNECT VALVES Bear i

48、n mind that the above disconnect valve is only one of many types presently used. Although all line-disconnect valves operate on the same principle, the details will vary. All manufacturer have their own design features. A very important factor in the use of the line-disconnect valve is its proper co

49、nnection. Hydraulic pumps can be seriously damaged if the line disconnects are not properly connected. If in doubt about the line disconnects operation, the aircraft maintenance manual should be consulted.,.,49,Basic Aircraft Systemshydraulic system,QUICK DISCONNECT VALVES The extent of maintenance

50、to be performed on a quick-disconnect valve is very limited. The internal parts of this type valve are precision built and factory assembled. They are made to very close tolerances. therefore, no attempt should be made to disassemble or replace internal parts in either coupling half. However, the co

51、upling halves, lock-springs, union nuts, and dust caps may be replaced. When replacing the assembly or any of the parts, follow the instructions in the applicable maintenance manual.,.,50,.,51,Basic Aircraft Systemshydraulic system,Hydraulic Fuses A hydraulic fuse is a safety device. Fuses may be in

52、stalled at strategic locations throughout a hydraulic system. They are designed to detect: line or gauge rupture（破裂）, fitting failure, other leak-producing failure or damage.,.,52,.,53,.,54,Basic Aircraft Systemshydraulic system,Hydraulic Fuses One type of fuse, referred to as the automatic resettin

53、g type, is designed to allow a certain volume of fluid per minute to pass through it. If the volume passing through the fuse becomes excessive, the fuse will close and shut off the flow. When the pressure is removed from the pressure supply side of the fuse, it will automatically reset itself to the

54、 open position. Fuses are usually cylindrical in shape, with an inlet and outlet port at opposite ends, as shown in figure.,.,55,Figure Fuse, operational view. 8-22,.,56,Basic Aircraft Systemshydraulic system,Hydraulic Fuses A stationary sleeve assembly is contained within the body. Other parts cont

55、ained within the body, starting at the inlet port, are a control head; piston and piston subassembly stop rod, a lock spring, and a lock piston and return spring. Fluid entering the fuse is divided into two flow paths by the control head. The main flow is between the sleeve and body, and a secondary

56、 flow is to the piston.,.,57,Basic Aircraft Systemshydraulic system,Hydraulic Fuses Fluid flowing through the main path exerts a force on the lock piston, causing it to move away from the direction of flow. This movement uncovers ports allowing fluid to flow through the fuse. The movement of the loc

57、king piston also causes a lock spring to release the piston subassembly stop rod, thus allowing the piston to be displaced by fluid from the secondary flow.,.,58,Basic Aircraft Systemshydraulic system,Hydraulic Fuses If the flow through the fuse exceeds a specified amount, the piston, moving in the

58、direction of flow , will block the ports originally covered by the locking piston, thus blocking the flow of fluid. Any interruption of the flow of fluid through the fuse removes the operating force from the lock piston. This allows the lock piston spring to return the piston to the original positio

59、n, which resets the fuse,.,59,Basic Aircraft Systemshydraulic system,Hydraulic Fuses There are two basic types of hydraulic fuses in use. 1. Pressure-drop type fuse It operates in such a way that it will shut off the flow of fluid if a sufficient pressure drop occurs across the fuse. Fluid flows as long as the spring holds the piston away from any of the holes, as in Figure 8-46, view (A).,.,60,Basic Aircraft Systemshydraulic system,Hydra