Patent GB-940869-A (GB)
Title: Safety control mechanism for pressure circuits
IPC: B30B15/14
Filed: 1959-11-20
Abstract: 940,869. Machinery safety devices; valves. E. HERION. Nov. 20, 1959 [Nov. 26, 1958; Nov. 27, 1958; Feb. 5, 1959], No. 39481/59. Headings F2J and F2V. Hydraulic apparatus such as a press or machine tool is controlled by a pair of valves with safety means for preventing operation of the apparatus should one of the valves fail to operate. As shown, a clutch 22 and a brake 23 are each controlled by a valve member 2 actuated by a piston 6 under the control of a pilot valve 8 which is actuated by a solenoid 18 controlled by a pair of switches (not shown) so connected that it is necessary that both switches be operated simultaneously to energize the solenoids 18. The valve members 2 control communication between conduits 3, 3<1> leading to the clutch and brake, and inlets 5 for pressure fluid and exhaust outlets 4. Fluid under pressure is derived from a connection 45 in a valve 40 which is normally held open by an abutment 29 engaging with an extension 24 of the valve stem, but in the event of failure of one of the valve members 2 to operate an unbalanced condition arises in pressure detector conduits 10<1> to cause movement in one direction or the other of a piston assembly 12<1> whereby either of a pair of recesses 28 on the piston assembly is brought opposite to the extension 24 to allow the valve 40 to close and to vent the conduits 5 through an outlet 43. Each detector conduit 10 consists of two passages, one connected with the outlet 3 of each valve member 2 and the other connected with a chamber 26 which connects with the outlet of its respective valve member 2 through a check valve 15 and passage 9. The check valves 15 are opened by adjustable stops 14 on downward movement of the valve members 2. A piston 12 is also connected to the chambers 26 and operates a switch 32 in the event of unbalance of the pressures in the chambers 26, the switch interrupting the supply of current to the solenoids 18. The switch 32 may also control a solenoid for operating the stem extension 24 of the valve 40 directly in which case the piston assembly 12<1> is dispensed with. To allow for slightly different timing of the operation of the clutch 22 and brake 23 the connection between the piston 12 and the switch 32 has lost motion, as has also the connection between the piston assembly 12<1> and the extension 24. Also for this purpose the abutments 14 for the check valves 15, and chokes 21 between the piston assembly 12<1> and the conduits 10<1>, are adjustable. The check valvs 15 may be housed as separate units with mechanical operating connections with the valve members 2. The valve 40 may be operated manually by a knob 46. In a modification, the outlets 3 from the two valve members 2 lead to a common delivery duct for operating a single element and the safety means is comprised solely by the piston 12 and switch 32 controlling the solenoids 18, the piston assembly 12<1>, the conduits 10<1>, and the valve 40 being omitted. It is stated that the solenoids 18 may operate the valve members 2 directly instead of through the pilot valves 8; also that the piston 12 may be replaced by a diaphragm or a pair of diaphragms. In a further modification, stated to be suitable also for controlling the mixing of two liquids, each valve member 2 controls only the communication between inlet for pressure fluid and an outlet, and the pressure detector conduits are connected through check valves with the spaces above the actuating pistons 6.