GB137864A - An improved valve apparatus for compressed air brakes - Google Patents

Abstract

137,864. Dubois, R. May 28, 1914, [Convention date]. Fluid-pressure; testing.-A train-pipe venting valve, constructed to operate only when fitted to the last vehicle of a train to enable the driver to test the continuity of the train-pipe, but operating also to apply the brakes, is adapted to open when the train-pipe pressure falls to a predetermined value and to reclose when this pressure has fallen to a predetermined lower value. The train-pipe is connected to the chamber 40 the outlet of which to the atmosphere is controlled both by a slide valve 3 and a lift-valve 2. When the device is mounted by the casing 8 on the coupling-hook 9 of the rear vehicle, a lever 4 is forced back to hold the valve 2 open. A piston 16, subject on its upper side to the train-pipe pressure and on its under side normally to the pressure of two springs 21, 22, has a finger 14 pivoted to it. The finger 14 is normally held in the position shown, ready for engagement with the stem 19 of the slide valve 3, by a spring 18 acting upon an arm of the finger. Assuming the running pressure to be 5 kg., the valve may be arranged to be insensitive to pressures between this and, for example, 3 kg. sufficient for normal application of the brakes. When the train-pipe pressure falls below 3 kg., the springs 21, 22 move the piston 16 upwardly until the cap 23 of the spring 21 abuts against the cylinder wall 25 and the valve 3 is moved by the finger 14 to uncover the port 27. The valve remains in this position until the pressure falls to, say, 1 kg. when the spring 22 is able to move the piston farther to contact its arm with the cylinder wall 20 whereupon the finger 14 is disengaged from the valve stem 19 and permits the spring 13 to return the valve 3 to the closed position. A restricted extension 28 of the port of the valve 3 prevents the valve from becoming completely closed unless the disengagement of the finger 14 is properly effective. To test the brakes, the driver applies the brakes slightly so as to disconnect the auxiliary reservoir from the train-pipe, and then allows the pressure to fall slowly. If there is no break in the train-pipe, the pressure on reaching 3 kg. will fall rapidly to 1 kg. The valve will also operate to increase the train-pipe pressure reduction in making full applications of the brakes and to apply the brakes automatically in the event of a slow fall of pressure.