GB926461A - Improvements relating to valve assemblies - Google Patents

Abstract

926,461. Fluid-pressure brakes. WESTING- HOUSE BRAKE & SIGNAL CO. Ltd. Feb. 23, 1961 [Feb. 24, 1960], No. 6458/60. Class 103 (1). A fluid-pressure control valve has a pressuresensitive element 37 to establish sealing of a closure member 35 with one 27, or other 28 of two valve seats, the element being movable relative to the closure member from a first position in which a restricted communication 42 between the two sides of the element is open, to a second position in which the communication is closed. The control valve is shown as applied to the quick service exhaust and inlet valve of the direct release triple valve described in Specification 909,616 to eliminate dragging brakes caused by fluctuations of brake-pipe pressure on release. The quick service valve comprises a pressure-sensitive diaphragm 37 carrying a valve housing 36 containing an axially movable closure member 35 urged towards the inlet 28 and exhaust 27 valve seats by a spring 40 of greater strength than a spring 39 which biases the diaphragm 37 in the same sense. A restricted communication 42, 41 across the diaphragm may be closed by movement of the closure member 35 against the spring 40 to contact the seating 43. If during release the diaphragm 12 is deflected, by brake pipe pressure fluctuation, sufficiently to seat the closure member 35 against exhaust seat 27 without detachment from the inlet seat 28, leakage past the seat 28 tends to build up pressure in the quick service volume 31 and, by passage 32a, under the diaphragm 37. The restricted opening 42 has sufficient flow capacity to release this build-up through passage 41 and 34 to atmosphere, the relative strength of the springs 39 and 40 keeping the inlet seating 28 closed and the seating 43 open. With a brake application pressure reduction, the rush of pressure into the volume 31 and chamber 38 when the inlet 28 is opened by upward movement of the diaphragm 12, is greater than the flow through the restriction 42 and the increased pressure below the diaphragm 37 together with the spring 39 overcomes the spring 40 to allow closure member 35 to seal off the valve seat 43 and thus seal the leakage escape path.