GB285209A - Improvements in or relating to railway vehicle braking systems - Google Patents

Abstract

285,209. Glascodine, R. T., Mc- Dermid, W. F., and Spencer, A. Dec. 24, 1926. Fluid-pressure.-A valve device for controlling the flow of air from the train-pipe to the several brake cylinders of an automatic vacuum brake apparatus in an application of the brakes in such a manner as to ensure a uniform rate of flow of air into the brake cylinders, irrespective of the excess of the pressure in the train-pipe over that in the brake cylinder as long as that excess is above a predetermined value, comprises a piston 8 subject on its under face to the pressure in the brake cylinder connected at 5 and on its upper face to the pressure in a chamber 1<c> connected to the train-pipe through the chamber 1<b> and a conical-opening 2. The stem 11 of the piston is slidable upon a tubular member 9, which normally rests upon the bottom of the casing, against. the action of a spring 16 disposed between a shoulder 15 on the member 9 and a collar 14 secured within the stem of the piston : Holes 17 through the piston form a restricted fairway for the passage of air to the brake cylinder. When the piston is moved to its extreme upper position by the rarefaction of the air in the train-pipe as when the brake is released, it is in line with holes or recesses 18 formed in the liner 4 which then provide free communication between the train-pipe and the brake cylinders. If during an application of the brake, the pressure in the chamber 1<c> above the piston exceeds that in the chamber 1<a> and the brake cylinder sufficiently to overcome the spring 16, a shoulder 12 on the piston stem is moved downwardly to restrict more or less the opening 2 thus maintaining a constant pressure difference between these chambers and a constant rate of flow of air to the brake cylinder. The pressure in the brake cylinders near the point of control is thus prevented from building up more rapidly than in those that are more remote.