GB941515A - Improvements relating to snap action pilot valve assemblies - Google Patents

Abstract

941,515. Fluid-pressure servomotor control Systems. WESTINGHOUSE BRAKE & SIGNAL CO. Ltd. Oct. 1, 1959 [Jan. 2, 1959], No. 240/59. Heading G3P. Air from a compressor passes through an inlet 14, past a check valve 25 to a reservoir via an outlet 15, a main valve 21 being seated both by the air and a spring 24. From the outlet 15 air also flows through a filter 37 to act on that part of the end of a pilot valve 44 within the area of a bead 45, the pilot valve being urged onto a disc 40 by an adjustable spring 52; when the air pressure is sufficient to cause initial unseating of the pilot valve the entire right end of the latter is then exposed to the air pressure so that the valve opens fully with a snap-action whereupon the left end of the pilot valve 44 seats on a second disc 42 and closes off the connection of a chamber 33 to atmosphere via an anhular space 47, the clearance between the pilot valve stem 49 and disc 42, the interior of a plug 43, the clearance between the stem 49 and a bush 50, and perforations in a cap 53. The chamber 33, which is partly defined by a diaphragm 31 attached to the main valve 21, is thus pressurised to deflect the diaphragm and open the main valve 21 so that the compressor delivery is discharged to atmosphere through a chamber 19. When the reservoir pressure falls the spring 52 and the throttling action of the stem 49 in the disc 42 causes the pilot valve 44 to seat on the disc 40 with a snap-action. The closure members 21, 25 and the discs 40, 42 are all of a standard size and are wholly or partly faced on each side with a resilient material e.g. rubber.