Patent GB-1281493-A (GB)
Title: Signal comparator fluid control circuit
IPC: F16P3/22
Filed: 1971-04-19
Abstract: 1281493 Fluid logic and switching circuits ROSS OPERATING VALVE CO 19 April 1971 [20 April 1970] 23314/71 Heading F1P Movement of a three-way piston valve 11 between the position shown in which an output line 12 is vented through a port 15 and its other position in which a constant supply pressure port 13 is connected to line 12 is effected by a return spring 16 and by fluid pressure when applied to a valve chamber 17 through a control line 21 having a disconnect valve 65 therein and also a dump valve 23, 24 which is connected by a triggering line 22 to first and second normally open 3-way control piston valves 29, 31; valve 29 having a constant pressure supply 32, and an output 33 connected to the supply input 34 of valve 31, valve 31 having its output 35 connected to line 28, valve chambers 36, 38 being respectively connected to AND and NOR gate means 37, 39 whereby the presence of neither or both signals A, B to the inputs of 37, 39 results in triggering line 28 being vented and dump valve 24 held closed thereby maintaining pressure in line 21 and also when one and only one signal is present resulting in pressurization of signal line 28, opening of dump valve 24, venting of control line 21 and closing of valve 11 thence venting of line 12. Line 12 may lead to the brake or clutch of a press, the control circuit of which includes two valves (not shown) which for safety reasons must be synchronised and which provide signals A, B. In operation and to pressurize line 12, line 21 must first be pressurized by manually depressing a normally closed reset valve 83 thereby connecting its constant supply input 84 to its output 82. This results in lifting of piston valves 65, 71, lowering of a piston valve 72, and pressurizing of line 21 from a supply 73 and through a check valve 78. On releasing reset valve 83, valves 71, 72, 65 return to the positions shown, chamber 17 is pressurized so that valve 11 connects the constant supply at 13 to line 12 and the pressure in chamber 17 is maintained through a branch line 19. Simultaneous application of signals A, B lifts valves 41, 57 and 44, 58 and allows valves 42, 43 to fall thereby connecting the constant supply 46 of valve 42 to chamber 36 of valve 29 thereby venting its outlet 33. In the meantime since valves 57, 58 are lifted, vents thereof are connected to chamber 38 of valve 31 thereby allowing the latter to fall, but since valve 29 is closed line 28 remains unpressurized and the dump valve 22 remains closed so that pressure in line 12 is unchanged. Assume signal B to be lost, valves 44, 58 return to the open position shown, valves 41, 57 remain lifted, valve 42 remains depressed and valves 44, 58, 29 become depressed resulting in supply pressure 32 being connected to trigger line 28 and dump valve 22 being opened, line 21 vented and valve 11 closed i.e. line 12 connected to exhaust 15. In a modification the dump valve comprises a single normally closed valve (101) Fig. 8 (not shown), the AND gate comprises a single normally closed valve (102) and the repressurizing means comprises a single normally closed valve 103.