Patent GB-1081645-A (GB)
Title: Fluid operable valves
IPC: B60T15/04
Filed: 1966-03-11
Abstract: 1,081,645. Fluid pressure brakes; valves. WESTINGHOUSE BREMSEN UND APPARATEBAU G.m.b.H. March 11, 1966 [March 12, 1965], No. 10847/66. Headings F2F and F2V.  The tractor in a tractor/trailer system is braked earlier than the motor vehicle, by utilizing a valve which comprises a pressuresensitive diaphragm piston 4 of variable effective area and a pressure-sensitive graduating piston 3, each piston being subjectible on one side to a common pressure from the tractor vehicle brake cylinders and the piston 3 being also subjectible on its rear face to a second pressure from a compressed-air storage tank, the pressure-sensitive pistons being cooperable with a slidable control valve 19 having an inlet and outlet formed by seats 30, 32 and 31, 34 respectively, such that in operation after a chosen increase in the common pressure, which results in a sudden fall in the second pressure acting on piston 3, the effective area of diaphragm piston 4 is reduced to alter the relative pressure variations in the two pressures. Pistons 3 and 4 are attached to a piston tube 2, slidable in a valve housing 1, and constitute a stepped piston 5. Diaphragm piston 4 rests on a supporting ring 6, which is secured by a collar 7 to tube 2, and a further ring 8, which can be moved on tune 2 and which is pushed by spring 9 against collar 7. In the rest position shown, atmospheric pressure prevails throughout the valve. Stepped piston 5 is held in its lower terminal position by springs 9 and 22, outlet valve 31, 34 is closed, the valve body 19 is pushed down so that inlet valve 30, 32 is open and the trailer brake pipe is connected to a storage tank via union 26, chamber 25, inlet valve 30, 32, chamber 27 and union 28. When pressure is built up in the storage tank air flows into the trailer brake pipe until the pressure built up in chamber 23 through choke 24 pushes stepped piston 5 upwards against spring 9 and 22 until valve seat 30 rests on seat 32. The control valve is maintained in this position, with the inlet and outlet valves closed, by a spring 29. When the pressure in the tractor vehicle brake cylinders is increased this is transmitted by union 21 to chamber 20 and diaphragm 4 pushes piston 5 and rings 6, 8 upwards against springs 9, 22. The outlet valve 31, 34 is opened and causes a sudden reduction in pressure in chambers 23, 25 through hole 18 in valve body 19. The stepped piston 5 now moves downwards. Owing to the initially large effective area of the diaphragm the pressure reduction is such as to cause a rise in pressure in the brake cylinders of the trailer which is greater than the pressure rise in the motor vehicle brake cylinders and causes the trailer to be braked earlier than the motor vehicle. Owing to the pressure in chamber 20 ring 8 and the attached portion of diaphragm 4 does not follow the downward movement of piston 5 and ring 6 and serves to reduce the effective area of the diaphragm to that portion attached to fixed ring 6. The trailer brake pressure now reduces uniformly in accordance with pressure increases in the motor vehicle brake cylinders. When the pressure in control chamber 20 is lowered, stepped piston 5 moves downwards, the inlet valve 30, 32 is opened and compressed air flows into chamber 25 and into the trailer brake pipe to release the brake. The valve may be actuated manually with the aid of a lever 39, which can be connected, for example, with the hand brake of the motor vehicle. The lever lifts cap 15, pin 35 and stepped piston 5, entrained via collar 36 against the action of a spring 38. Air is released from chamber 25. On release of the hand brake outlet valve 31, 34 is re-closed.