Patent GB-581007-A (GB)
Title: Improvements relating to fluid pressure braking apparatus
IPC: B60T15/30
Filed: 1943-08-21
Abstract: 581,007. Fluid-pressure brakes. TOMLINSON, A. V. (Westinghouse Air Brake Co.). Aug. 21, 1943, No. 13649. [Class 103 (i)] [Also in Group XXIX] The initial movement of a slide valve or valves of a control valve device for fluid-pressure brake equipment of the type that is operative upon a pressure reduction in a brake or control pipe to effect an application of the brakes is assisted by the action of a permanent magnet which when the valve is in the normal position provides a force which is slightly less than the static friction of the valve. The emergencyacting portion of a control valve device is shown and comprises main and auxiliary slide valves 18, 19 operated by a piston 11 upon a pressure reduction in the control or brake pipe 10. Movement of the valve 18 to the right by the piston is effected with lost motion by a plunger 75 slidable against the pressure of spring 24 in an extension 76 of the valve stem 20. The extension 76 is slidable in the inner part of an extension 26 of the casing 2. The normal position of the piston and valves is determined by abutment of a collar 30 of the stem 20 and a projection 31 of the valve 18 on a stop 28 slidable in the casing extension 26 against the pressure of a spring 29 and held in the position shown by a shoulder 27 on the fixed body of the device. The valve 18 is held to its seat against the pressure differential, which acts on it during an application by a rocking pin 35 subject to the pressure of a spring 37 and of that in the reservoir 6 acting in chamber 38. A brake-pipe venting valve 42 normally seated by a spring 47 is operable by a piston 41, the chamber 51 of which is normally connected to atmosphere through a restricted port 54, chamber 53 and passage 49. The service portion (not shown) of the device operates upon an increase of pressure in the brake pipe 10 after an application to supply the emergency reservoir 6 and to exhaust the brake cylinder 8 and upon both service and emergency brake-pipe pressure reductions supplies the brake cylinder from the auxiliary reservoir through passage 56. Normally the brake pipe supplies the quick-action and valve chambers 16, 15, through passage 14, chamber 12, restricted port 57 and passages 17. Upon a service brake-pipe pressure reduction, the piston 11 and valve 19 move relatively to valve 18 until the plunger 75 contacts the valve 18, thus connecting chambers 15, 16 to atmosphere port 60 through passages 58, 59, so as to limit the pressure differential acting on the piston to a value that is insufficient to effect further movement, but if the pressure reduction is at emergency rate, the plunger 75 yields and the valve 19 uncovers passage 61, thus connecting chambers 15, 16 to chamber 51 through passages 61, 52. The valve 42 is thus opened and the brake pipe vented to atmosphere through passages 14, 46, 49 until the loss of pressure in chambers 15, 16 through port 54 permits spring 47 to re-close the valve. By the venting of the brake pipe the pressure differential on the piston 11 becomes sufficient to move the main valve 18 whereby the reservoir 6 is connected to the brake cylinder 8 by passages 39, 63, 64. To prevent undesired movement of the piston and valve 19 to emergency position, which may happen particularly if, through dirt or inadequate lubrication, the static friction of these parts is considerably greater than the kinetic friction, the valve stem 20 and a relatively fixed part such as the stop 28 are respectively provided with magnets 73, 72 having like poles normally closely adjacent so as to provide a force slightly less than the normal static friction and tending to move the piston and valve to application position, but which falls off rapidly as the distance between the poles increases on movement of the piston. Opposing magnets 74, 77 may also be provided on the main valve 18 and the stop 28 to assist similarly the initial movement of that valve. When the brake-pipe pressure is raised for release of the brakes and charging, the pressure differential on the piston 11 is at first sufficient to overcome the stop 28 so that the brake cylinder 8 is connected to the brake pipe to boost the pressure therein, through passages 64, 66, check valve 67 and passages 69, 46. If the chambers 15, 16 tend to become overcharged, pressure fluid flows therefrom to the reservoir 6 by check valves 70, 71 and passage 40.