GB214092A - Improvements in valve mechanism for railway brakes - Google Patents

Abstract

214,092. Drolshammer, I. May 2, 1923. Fluid-pressure. - Relates to compressed air brakes wherein, when the brakes are applied, the brake cylinder pressure first rises rapidly to a predetermined value, and then increases more slowly to its full value, and comprises a piston K controlled by train pipe pressure which cooperates with a slide-valve s so that a rapid initial flow of air to the brake cylinder is permitted, but after the desired minimum brake pressure has been reached, any further supply of air takes place through a throttled passage. The piston K is provided with an annular recess 4, and its rod d bears against a plate T<2> subject to the pressure of springs F<2>, whilst the slide-valve s, which slides on the rod d and is subject to the pressure of a spring F<1>, has a broad rib having channels 2 through it, the piston and slide-valve being adapted to work in a sleeve L mounted in a cylinder D. With the ports in the positions shown, air passes from the train pipe through a port e, Fig. 2, a passage w<4> in a rotary cock H, and a channel o, Fig. 4, to the space above the piston, whereby the piston and slide-valve are held depressed against the pressure of the spring F<2>. At the same time, the auxiliary reservoir B is charged through non-return valves V<2>, V, Fig. 2, and the passage E<1>, and the brake cylinder C exhausts through the passages g, g<1>, chamber a, ports h, chamber k<1>, and ports i, i<1>. When train pipe pressure is reduced to apply the brakes, the piston K and slide-valve s rise, so that the latter first closes the discharge ports h and then uncovers a port k in the sleeve L, so that air from the auxiliary reservoir can flow rapidly to the brake cylinder through the channel E, the large through-passage w<1> of the cock 1@1, the channel 1, chamber 2, port 3, recess 4 of the piston, port 5 and channel 6. Fig. 5, chamber k<3> in the cylinder D, ports k, chamber a, port g<1> and passage g. Simultaneously air is fed slowly from the channel E, passage w<1> and constricted passage w<2> into the chamber k<3>, and thence to the brake cylinder as above, whilst train pipe air displaced by the piston X can pass to the brake cylinder through the port x<3>, channel o<1>, port x<1>, chamber a, port g<1> and passage g. When the reduction of train pipe pressure is such that the brake cylinder pressure has leached the desired minimum value, the piston K is adapted to close the ports 3, 5, so that the free flow of air is cut off, and the brake pressure can only be built up through the throttled passage w<2> of the cock, as the piston K simultaneously closes the port x<3> to cut off the train pipe from the brake cylinder, though a further small port above x<3> may be provided to allow the train pipe to continue feeding the brake cylinder very slowly. In order that a rapid reduction of train pipe pressure may result in a rapid feed of train pipe air to the brake cylinder, a large port x<2> is provided in the sleeve L just above the port x<1>, which remains open until the back pressure from the brake cylinder moves down the slide-valve s. By rotating the cock H so that the large through passage w<1> registers with the chamber k<3> rapid braking may be obtained, as the throttled passage w<2> is cut out and the circuitous free path is replaced by the direct free path w<1>, k<3> - - g, but further passages may be provided in such case to give still the alternative circuitous and direct paths, and be so portioned as to effect rapid braking whilst retaining the feature of a more rapid initial feed to the brake cylinder. By rotating the cock so that the passage w<1> registers with the passage y, the auxiliary reservoir is cut off from the brake cylinder, which exhausts through the passages y, w<1>, and y<1>, Fig. 2. In Fig. 1, the valve mechanism is shown in conjunction with the means for varying the brake pressure according to the load described in Specification 188,002, whilst the piston K and slidevalve s are similar to those described in Specification 164,041.