Patent GB-314179-A (GB)
Title: Improvements in devices for controlling the brakes of railway vehicles
IPC: B61H9/00
Filed: 1928-05-10
Abstract: 314,179. McDermid, W. F. May 10, 1928. Fluid-pressure.-In a valve for effecting the proportional application of a, steam or compressedair brake on a locomotive by variation of the vacuum in the train-pipe by which the vacuum brakes on the train are applied, the steam or compressed air valve is actuated by a piston subject on the one side to atmospheric pressure and on the other to the train-pipe vacuum and to the pressure of a spring. A hand-operated cock for applying and releasing the brakes is also provided. A piston 3 slidable in a chamber 2, 2<1> of the casing 1 is subject on its under side to the vacuum in the train-pipe through the passage 4 and to the pressure of a spring 10 and on its upper side to atmospheric pressure through the passage 7, a pasage 8 in the hand-control cock C and a port 9 in the casing. The piston has a stem 25 in which is slidable the extension 24 of a sleeve 22 arranged to engage the rod 19 of a pilot valve controlling the main steam or compressedair valve 16 the chamber 11 of which is connected to the steam supply by the passage 15, 14, 12, the passage 14 being in the cock C and the passage 12 leading to a port in the flange 45. The passage 4 has alternative connections to the train-pipe through the branch 5 or a port in the flange 45. A branch 6 connects to the train-pipes near the drip-bulb to clear water from the valve to a branch 42 which is connected to the main reservoir of the Westinghouse system when compressed air is used. The brake cylinder is connected at 18 and with the parts in the normal position shown, exhausts through the sleeve 22, chambers 23 and passage 31. The pressure-fluid in the chamber 11 leaks through the passage 21 and holds the valves 16, 19 closed. If air is admitted to the train-pipe to apply the brakes, the piston 3 is raised by the spring 10, first seating the sleeve 22 on the stem 25 to cut off the brake cylinders from the exhaust passage 31 and then lifting the pilot valve 19 to vent the upper side of the valve 16 which is thus lifted by the pressure acting on its under side to connect chambers 11, 17 and supply the pressure-fluid to the brake cylinder. When the pressure in the cylinder acting upon the sleeve 22 and stem 25 corresponds to the rise of pressure in the trainpipe and chamber 2 the piston 3 returns sufficiently to close the valve 19 and thus also the valve 16. The locomotive brakes may also be applied by turning the cock C by its handle 32 into a position in which the passages 15, 12 are still connected but by the passage 28 and the passage 8 is out of register with the passage 7 so that the piston chamber 2<1> is cut off from the atmosphere and the pressure therein equalizes by leakage past the piston with that in the chamber 2. The spring 10 thus lifts the piston to open the valve 16. The brakes may be subsequently released by turning the valve to the position shown in Fig. 5, in which the pressure-fluid supply passage 15 is disconnected and the chambers 17, 23 are connected. The lower end of the spring 10 may rest on a seat adjustable by a screw to vary the pressure of the spring. The valve casing may be designed for attachment to the flange that is sometimes provided on the ejector for a steam brake valve.