GB946122A - Improvements in or relating to valve means for controlling release of pressure from fluid pressurised systems - Google Patents

Abstract

946,122. Fluid-pressure brakes. KNORRBREMSE G.m.b.H. Dec. 2, 1960 [Dec. 5, 1959], No. 41642/60. Heading F2F. A pressure release valve comprises a safety valve to limit the pressure in the system, an inlet valve controlling the flow into a control chamber containing a spring-loaded piston which closes the inlet valve at a predetermined chamber pressure, continuous venting means from the chamber to atmosphere and piston movement responsive means to provide linear pressure drop in the system by varying the venting rate from the chamber by movement of the inlet valve. The venting valve 9, which may be used for controlling the release of pressure from a driver's brake valve, is connected to a pressure system represented by a reservoir 5 to which fluid may be introduced by a shut-off member 1 and a nozzle 3. The valve 9 has a chamber 7 connected to the system and separated by a partition 11 from a control chamber 13. The partition has an axial bore 19 providing a valve seating 17 in the chamber 7 and having radial vent passages 21. The control chamber 13 is limited by a piston 15 having a pistonrod 23 extending with clearance through the bore 19 and formed with a sealing plate 25 co-operating with the valve seat 17. The piston-rod has an axial bore 27 closed at the end remote from the plate 25 by a sealing plate 33 loaded by a spring 31 in a chamber 35 vented to atmosphere. An annular groove 37 in the piston-rod allows a large through-flow from the chamber 13 to the vents 21 when the valve 17, 25 is wide open. When filling the reservoir 5 by opening the shut-off member 1, compressed air flows into the chamber 7 and, as valve 17, 25 is held open by spring 31, into control chamber 13. At a predetermined low-pressure stage the piston 15 moves against spring 31 to close the valve 17, 25 to a condition where the flow through the valve is in equilibrium with the venting through the passages 21. Above this pressure the safety valve 33 opens and prevents a further rise in pressure in the reservoir 5. On closing the member 1 the pressure in the reservoir falls slightly as the valve 33 closes and venting continues by way of the control chamber 13. Since the piston 15 in conjunction with spring 31, valve 17, 25 and vent passages 21 maintain a constant pressure in the chamber 13, a pressure drop linearly dependent on time is produced in the system. When the system pressure falls to that in the control chamber 13, the piston moves to the right to open the valve 17, 25 and to connect the passages 21 with the chamber 13 by the groove 37. The venting retardation caused by the decreased pressure difference is thus substantially compensated by the reduced flow resistance and pressure drop continues substantially linearly until the system is fully vented.