SYSTEM PROTECTION VALVE

Abstract: A protection valve for fluid operatet systems, having two or more valve elements each of which opens against a bias to admit fluid under pressure to an associated fluid operated system and comprising a plunger (40) biased toward a position wherein it closes off an outlet port for connection to the associated system and carrying a non-return valve (44) which is movable to the plunger (40) such that communication between a bleed-hole (52) through the non-return valve (44) and the outlet port associated with the valve element is cut off below the closing pressure of the valve element. Because the bleed by-pass (52) is only active between valve opening and closing pressures, all sound systems can be protected against failure in any other system below valve closing pressure.

Description: SYSTEM PROTECTION VALVE This invention relates to protection valves for fluid operated systems, for example, the service brakes, spring operated brakes and auxiliary systems of a vehicle. Such valves :iae to distribute fluid, normally compressed air, to the system in a required sequence, to protect each system against loss of pressure in other systems and to enable all sound systems to be charged to a predetermined miilililum operating pressure following system failure due to air leakage. The unit also enables the service systems to augment the supplementary systems. In general, a pro'-ect.ion valve include a housing containing two or more valve elements each of which opens against a bias to admit fluid under pressure to an associated fluid operated system and comprises a plunger biased toward a position wherein it closes off an outlet port for connection to the associated system and carrying a non-return valve which is movable relative to the plunger, to uncover a bleed hole in communication with the said port. The non return valves isolate thc respective systems in the event of excessive rediiction in pressure due to, for example, failure of the air supply system. In the event of excessive loss of air pressure in one of the service systems, the plunger resets thus isolating the failed system. The remaining systems can be charged but only to-the opening pressure of the element in the failed system. This pressure normally being set at a level sufficient to enable the remaining service system to provide secondary or residual braking. In multiple systems, it is often desirable to maintain preferential charging to the main service braking system and, to this end, one or more additional plunger type valve elements each associated with a supplementary system are connected (in parallel) to a flowpath linking the outlet ports associated with the service systems, the flow into the said flow-path at each junction being through a non-return valve. Excessive air leakage in one of the supplementary systems causes air pressure in the service systems to fall to the closing pressure of the element in the failed system, the air in the remaining supplementary system(s) being retained by the non-reti1rn valve in the plunger. The elements in the supplementary system are set so that their opening pressures are sufficient to eiiable the service systems to provide secondary or residual braking in the event f supplementary system failure de to air leakage. The valve elements associated with the supplelentary systems could not, however, be raade identical ith the service system elements silice the b3.eed hole is active at zero pressure and above, so that in the event of a supplementary system failure, Lhe service reservoirs feed-ng the supplementary system would also fail. What we now propose in accordance with the present invention is a system protection valve having two or more valve elements each of which opens against a bias to admit fluid under pressure to an associated fluid operated system and comprises a plunger biased toward a position wherein it closes off an outlet port for connection to the associated system, and carrying a non- return valve which is movable relative to the plunger such that communication between a bleed-hole through the non-return valve, and the outlet port associated with the valve element is cut-off below the closing pressure of the valve element. Because the bleed by-pass is only active between valve opening and closing pressures, all sound systems can be completely protected against failure in any other system below valve closing pressure. Another advantage of a protection valve according to this invention is that the valve elements can be identical, thus facilitating manufacture, even for multiple systems in which service systems are charged preferentially. Other features of this invention are referred to in the .lppendartt claims and in the following description of a preferred embodiment of the invention with reference to the accompanying drawings of wr.ih: Figure 1 is a diagram of a typical pneumatic vehicle braking circuit in which compressed air is distributed to the various systems via a system protection valve according to this invention. Figure 2 is a part cross-section of the system protection valve used in the circuit of Figure 1 having fout identical valve elements, and Figure 3 is an enlarged diagramatic view of one of the said valve elements and Figure 4 is an enlarged view similar to Figure 3 but of a, modified valve element. Figure 1 shows a system protection valve 10 connected in a pneumatic vehicle braking circuit having a service braking systems 12, spring parking brake system 14 and auxiliaries 16. Compressed air is delivered to the inlet 1 of the system protection valve 1C from a reservoir I8 connected to a compressor (not ShOTvTL) and is distributed to the service system L2 via service reservoirs 20 connected to outlet ports 21 ard 22. The spring parking brakes and auxiliary systems are connected to supplementary outlet ports 23 and 24 of the system protection valve 10. Referring now to Figures 2 and 3, tht valve 10 has four identical valve elements W, X,.Y, Z of which elements W and X are associated with the service systems and elements Y and Z associated sith the supplementary systems 14 and 16, communicate with a flow path 26 interconnecting the outlet ports 21 and 22 via spring loaded non-return values 23 and 30. Fionce, the service systems are charged preferentially. Each of the valves W, X,Y and Z have a plunger 40 which is sealed by n O-ring 42 and loaded by a pre-set spring dete,.nining the opening pressure of the valve element. The plunger 40 carries a non-return valve 44 having a boss 45 which is a clearance fit in a cylindrical recess 46 of the plunger 40, and seating on a circular lip or rim 48 around the face of the plunger. A smaller diameter rim or lip 50 on the opposite face of the non-return valve 44 co-operates with a fixed seat on the valve housing to close off communication with the inlet port 1 in the case of valve elements W and X or the flowpaths 26 in the case of supplementary valve elements Y and Z. The valve 44 has a bleed hole 52 normally closed by a spring-loaded bleed non-return valve 54 which seats on the face of the boss 45 within the recess 46 to close off communication vin. the clearance 56 between the boss 45 and the recess 46 (represented in figure 3 by a floT¯ath shown dotted) wih the space defined by lip or rim 48 another end face of the plunger. To charge the circuit, air from the compressor or supply reservoir i8 s directed to valve elements W and X pressure thus building-up through the bleed holes 52 to act on the large seat diameter defined by the lip or rim 48. When the lo-d balances the opposing spring load, the plunger 40 lift to ptzrmit air flowing through the bleed hole 52 to pass J:) the service reservoirs via ports 21 and 22. The main air flow valve 44 opens when the pressure of air increases to the pcint at which the pressure acting on the seat defined by the smaller lip or rim 50 equals the opposing spring load. This pressure is th valve opening pressure. Once the valve is open, this pressure acts on the Spring diameter which is larger than the diameter of lip 50 so providing a further boost to valve opening. In this state, the valve 's4 acts as a non-return valve in the direction of flow. After opening of the service valve elements W and X, air passes through the supplementary non-return valves 28 and 30 to valve elements Y and Z thus charging the supplementary systems. When charging ceases, the non-return valves 44, 28 and 30 re-seat but the plunger 40 remain unseated by virtue of back pressure in the associated systems. As air pressure falls through usage or as a result of failure, the valve elements close at a pressure equal to the spring load divided by the area of O-ring 42 internal diameter. This is referred to as the closing pressure. Upon excessive loss of pressure in one of the service system the appropriate plunger 40 reseats under the action of the associated spring load, thus isolating the failed system. The remaining sound system can still be charged but only to the opening pressure of the element in the failed system. The elements associated with the service systems are set such thai. their opening pressures are sufficient to enable the remaining serI.ce system to provide secondary or residual brking. Thus operation, in the event of service system failure, is as fcr the convention protection valve described above. In the event of a suppl.ementary system fai1.ure, however, performance is much improved since ail sound systems can be pumped up from aero pressure.This is because the bleed by-pass is inactive when the plunder 40 seats upon the floating valve 44 below closing pressure. In other respects the valve operates as c conventioilal valve to protect against supplementary system failure. A modified valve element which can be used instead of the valve element shown in Figures 2 and 3, is shown in Figure 4. In this case the non-return valve 44 has an off-set bleed hole 52 communicating with an annular recess 60 surrounding the valve stem 70, one side of the non-return valve 44. This recess is normally covered by a spring loaded bleed non-return valve 54 housed in a recess 62 in the face of the plunger 40. There is no circular lip 48 but the plunger seats directly on the valve 44 and the diameter of the recess 69. is greater in diameter than the outlet opening 64 which, in the closed position is covered by the opposite side of the valve 44. The bleed non-return valve comprises a flexible disc 66 of rubber or the like, which is pressed into its closed position (Figure 4 b a spring loaded domed element 68 surrounding the stem 70 of the non-return valve and carried in a stepped recess 72 in the plunger concentric with the recess 62. In operation, the modified valve element of Figure 4 is.identical with the valve elemet of Figure 3.

Claims: Claims: 1. A protection valve for fluid operated systems, having two or more valve elements each of which opens 'against a bias to admit fluid under pressure to ar associated fluid operated system and comprises a plunger biased toward a position wherein it closes off an an outlet part for connection to the associated system, and carrying a non-returij valve which is movable relat.ive to the plunger such that communication between a bleedhole through the non-return valve, and the outlet part associated with the valve element is cut-off below the closing pressure of the valve element. ?. A valve according to claim 1 wherein one or more of the valve elements communicates for the supply thercto of fluid under pressure vla a non return valve with the outlet part or another of the valve elements whereby the fluid operated systems associated with the said other valve element is harged preferentially. 3; A valve according to ciaim 1 or rlai.m 2 wherein the bleed hole in non-ieturn valve is normally closed by a spring loaded bleed non-return valve carried between in z recess It the plunger 4. A valve according to claim 3 wherein the non-return valve¯has on one side a central boss through which the bleed hoJe passes and wherein the boss is sliding received in the said recess in the plunger, the recess also containing the spring loaded non-return valve which is biased against the boss to close the bleed hole. 5. A valve according to claim 3 wherein the bled hole opens into a recess on one side of the non-return valve confronting the plunger and wherein the bleed non-return valve is disposed in a recess in the end face of the plunger an' comprises a spring loaded domed element pressing a Jlexi.ble disc to close the bleed hole recess.

Inventors: BAINES, ROBERT GEORGE, COUPLAND, RALPH
Applicants: CLAYTON DEWANDRE COMPANY LIMITED
Application year: 1980
Main classification: B60T17
IPC codes: B60T11