Patent GB-1264119-A (GB)
IPC: F16K17/10
Filed: 1968-05-10
Abstract: 1,264,119. Fluid-pressure servomotor systems. CROSBY VALVE & ENG CO. Ltd, L. W. LAMBURN and K. W. WEST. Aug.7, 1969 [May 10, 1968; Aug.20, 1968], Nos. 22409/68 and 39868/68. Heading G3P. A pressure relieving system which is adapted for use in association with a vessel 2, comprises a pressure relief valve 1, having a differential pressure actuator 3, a three-way pilot valve 4, and a pilot operator 5, the pressure within vessel 2 determining the state of the operator 5 and hence also the state of valve 4 and both the operator 5 and the valve 4 being connected through line 51 and port 37, respectively, to a source of pressure which may be independent of the vessel 2 or derived therefrom. The relief valve 1 has inlet and outlet connections 7 and 8 respectively and a closure member 11 carried by a stem 12 which is loaded by a spring 13, whilst the actuator 3 comprises a diaphragm which is subjected to the force of a spring 25 and has depending therefrom a rod 19, a coupling tube 26 providing a lost motion connection between the rod and spindle. Valve 4 comprises a single-beat lift valve member (36), Fig. 3 (not shown) which is subjected to the action of a spring (40) tending to move the member into a position such that ports 37 and 38 are in communication, and which is connected to a diaphragm (32) movable in opposition to the spring upon pressurization of line 34 to place ports 38 and 39 into communication with one another. The operator 5 includes an adjustable Bourdon tube (40A), Fig, 4 (not shown) which is connected'to the vessel 2 and which flexes upon the vessel pressure reaching the maximum desired value so moving a pivotable flapper (60) to open a relief port (59). Such opening initiates a positive feedback (56), (57) tending to swing the flapper still further from the nozzle and allows the diaphragm (32) of valve 4 to move under the effect of its spring (40), both the flapper swing and the diaphragm movement, resulting from the fact that opening of the nozzle decreases the pressure transmitted from line 51 to both the feedback and to the diaphragm. In operation, with the pressure in vessel 2 below a predetermined value, the relief valve is closed and the underside 22 of diaphragm 21 is open to atmosphere via port 39 of valve 4. Upon the predetermined value being reached, the Bourdon tube flexes, the nozzle (59) opens and so valve 4 changes state to permit pressurization of line 34 and hence of the underside 22 of diaphragm 21 thereby giving a rapid and positive opening of the relief valve. Decrease in pressure within vessel 2 reverts operator 5 and valve 4 to their initial states and the relief valve seats under the force of spring 13. Should the system fail, then the lost motion connection 26 permits independent operation of valve 1. In various modifications, Figs. 7 to 13 (not shown) pressure to the actuator 3 may be supplied. to the top side of its diaphragm 21, the operator 5 may be connected to the vessel 2 by a bulb which contains a heat responsive medium adapted to transmit a pressure impulse, the valve 4 may be operated by a solenoid the supply of current to which is controlled by operator 5.