飞机液压系统活门介绍.ppt

1、Basic Aircraft system Valves of Aircraft Hydraulic System,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 normally

2、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.,Basic Aircraft Systemshydraulic system,HYDRAULIC SYSTEM VALVES FLOW CONTROL VALVES For hydraulic component

3、s 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 (选择活门) 2. check valves (单向活门) 3. sequence valves (顺序活门) 4. priority valves (优

4、先活门) 5. quick disconnect valve (快断活门) 6. hydraulic fuses (液压保险),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 the landing gear, or

5、to select the position of the wing flaps. Two commonly used types of selector valves:,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 a unit is not being act

6、uated. 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.,Basic Aircraft Systemshydraulic system,VALVES-SELECTOR VALVES Open-center val

7、ve 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 valve from the pump to the n

8、ext selector valve and on to the reservoir. Figure 8-37, view (A),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 (refer back to Figure 8-17) must off

9、-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.,Basic Aircraft Systemshydraulic system,VALVES-SELECT

10、OR 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 to its neutral position. Some open-cente

11、r valves have an automatic feature that causes them to move to the neutral position when the pressure rises to a specified value.,Basic Aircraft Systemshydraulic system,VALVES-SELECTOR VALVES Open-center valve When the gear selector is moved to the GEAR UP position, poppets 2 and 5 open, and fluid f

12、rom the pump flows around poppet 2, while the return fluid flows around poppet 5 as in Figure 8-37, view (C).,Basic Aircraft Systemshydraulic system,VALVES-SELECTOR VALVES Closed-center valve 1. Plug-type closed-center valves are often used in aircraft hydraulic systems. In one position, the pressur

13、e 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,Basic Aircraft Systemshydraulic system,Poppet Valve

14、 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 through a valve guide. In most applications a pressure differenti

15、al helps to seal the valve and in some applications also open it.,Basic Aircraft Systemshydraulic system,VALVES-SELECTOR VALVES Closed-center valve 2. poppet-type selector valve (提升阀,菌形活门) A more positive shutoff of fluid may be provided by using a poppet-type selector valve, such as the one shown i

16、n 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. The fluid from the opposite side of the actuator piston is pushed out o

17、f the cylinder, around poppet three, and back to the reservoir.,Basic Aircraft Systemshydraulic system,VALVES-SELECTOR VALVES Closed-center valve 2. poppet-type selector valve When the gear selector handle is placed in the GEAR DOWN position (view B), poppets 1 and 4 are off-seated, and poppets 2 an

18、d 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.,Basic Aircraft Systemshydraulic system,VALVES-SELECTOR VALVES Closed-center valve： 2. poppet-type selector valve In a closed-center hydraulic system,

19、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 position of any selector valve.,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVE

20、S 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 valves.,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES Types of Check Valves 1.Fla

21、p type - this type of check valve is not used in hydraulics,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES Types of Check Valves 2. Ball Type Too heavy and has too much inertia to move,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES Types of Check Valves 3. Poppet type valve i

22、s the preferred type that is used in hydraulics now.,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES 3. Poppet type valve is the preferred type that is used in hydraulics now. The front of the poppet (left side of the picture above) sits snugly on the hard seat (darker shaded areas on the

23、 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.,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES 3. Poppet type valve is the preferred type that is used in hydraulics now. Since P1P2 , t

24、he 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 flow from the right side of the poppet, then P2P1 and the pressure forces the poppet against the valve seat, closing

25、 off the opening. Thus the fluid is allowed to flow through in one direction only.,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES Check valves are designed so as not to tolerate leakage. The purpose of the light spring is only to keep the poppet on the seat. Most manufacturers use sharp-

26、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.,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES Check valves are made in two general designs to serve two differen

27、t 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 are commonly called inline check valves. In the other design, the check valve is not complete within itself because it does not have a housin

28、g 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 and, as such, shares the housing of that component.,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES There are several types of in-l

29、ine 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 direction. 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

30、a cone rather than by a ball.,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES Neither of these check valves allows an entirely free flow in 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 pressur

31、e in a gear-type hydraulic pump. The spring force determines the pressure needed to open the check valve.,Basic Aircraft Systemshydraulic system,VALVES-CHECK VALVES Swing-type valve（回转阀） Some applications for a check valve cannot tolerate the opposition to the flow of fluid, and if this is the case,

32、 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 passage 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, flui

33、d attempting to flow in the opposite direction will force the disc over the opening and prevent any flow.,Basic Aircraft Systemshydraulic system,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

34、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 against the air load requires every bit of pressure possible to get the gear up. Figure 8-41,Basic Aircraft Systemshydraulic system,ORIFICE CHECK VALVES An orifice c

35、heck 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 restricted, While fluid leaving the gear-up side of the actuator is restricted by the orifice in the check valve. Figure 8-41,Basic Aircraft Systemshydraulic system,

36、VALVES-SEQUENCE VALVES Modern aircraft with retractable landing gear often have doors that close in flight to cover the wheel 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 va

37、lves which allow a flow in only one direction, but may be opened manually to allow fluid to flow in either direction. Figure 8-42,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

38、this system, the gear door actuating piston opens the sequence valve when the doors are fully open, allowing fluid 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,Basic Aircraft Systemshydraul

39、ic system,VALVES-PRIORITY VALVES Priority Valves Priority valves are similar to sequence valves, except 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 pr

40、essure than the main landing gear, and the valve will shut off all the flow to the main gear until the doors 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,Basic Aircraft S

41、ystemshydraulic system,QUICK DISCONNECT VALVES Quick-Disconnect Valves Quick-disconnect, or line-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 im

42、mediately behind the power pump.,Basic Aircraft Systemshydraulic system,QUICK DISCONNECT 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 disconne

43、ct valve units consist of two interconnecting sections coupled by a nut when installed in 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,Basic Aircraft Systemshydraulic system,QUICK DISCONNECT

44、 VALVES The top illustration of Figure 8-45 shows the valve in the LINE-DISCONNECTED 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 t

45、he LINE-CONNECTED position. When the valve is being connected, the coupling nut draws the two sections together.,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 poppe

46、t off its seat and permits fluid to flow through that section of the valve. 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.,

47、Basic Aircraft Systemshydraulic system,QUICK DISCONNECT VALVES Bear in 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 impo

48、rtant factor in the use of the line-disconnect valve is its proper connection. 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.,Basic Aircraft Systemshyd

49、raulic system,QUICK DISCONNECT VALVES The extent of maintenance 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

50、 replace internal parts in either coupling half. However, the coupling 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.,Basic Aircraft Systemshydraulic system,Hydraulic Fuse

51、s A hydraulic fuse is a safety device. Fuses may be installedatstrategiclocationsthroughouta hydraulic system. Theyaredesignedtodetect: lineorgauge rupture（破裂）, fitting failure, other leak-producing failure or damage.,Basic Aircraft Systemshydraulic system,Hydraulic Fuses Onetypeoffuse,referred toas

52、theautomatic resetting type, is designed to allow a certain volume of fluid per minute to pass through it. If the volume passing throughthefusebecomesexcessive, thefuse will close and shut off the flow. When the pressure is removed from the pressure supply side of the fuse, it will automatically res

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

54、scontainedwithin 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 secon

55、dary flow is to the piston.,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 thefuse. Themovementofthelockingpi

56、stonalsocausesa lock springtoreleasethepistonsubassemblystop rod, thus allowing the piston to be displaced by fluid from the secondary flow.,Basic Aircraft Systemshydraulic system,Hydraulic Fuses If the flow through the fuse exceeds a specified amount, the piston, moving in the direction of flow ,wi

57、llblocktheportsoriginally covered by the locking piston, thus blocking the flow of fluid. Any interruption of the flow of fluid through the fuse removes theoperatingforcefromthelockpiston. This allows the lock piston spring to return the piston to the original position, which resets the fuse,Basic A

58、ircraft 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 a

59、way from any of the holes, as in Figure 8-46, view (A).,Basic Aircraft Systemshydraulic system,Hydraulic Fuses 1. Pressure-drop type fuse If a break should occur in a line beyond the fuse, the pressure on one side will drop, and the pressure on the other will force the piston over to cover the holes in the body and stop all flow of fluid. Only when pressure on the normal flow inlet side is greater than it is on the outlet side will the fuse close the line, so a reverse flow is not restricted in any way