Patent GB-865419-A (GB)
Title: Improvements in or relating to hydraulic safety valves
Inventor: MILNER HARRY LAWLEY
IPC: F16K17/10
Filed: 1956-05-16
Abstract: 865,419. Fluid-pressure servomotor-control systems; valves. ROTOL Ltd. May 16, 1957 [May 16, 1956], No. 15309/56. Class 135. An hydraulic safety-valve comprises a main valve chamber 12, Fig. 5a, having therein a piston 13 carrying a main valve member 17 urged by a spring 18 to close communication between a pressure inlet 14 and an exhaust outlet 15, a pilot chamber 27 disposed within the main valve chamber and having an inlet 26, a pilot piston 28 carrying a pilot valve member 23 and urged by a spring 29 to close the inlet 26, a passage 30 through the main piston and valve connecting the pilot chamber 27 to exhaust, an orifice 31 in the main piston permitting a restricted flow of pressure fluid to the left-hand side of the piston and a further orifice 32 in the pilot piston 28 permitting restricted flow to exhaust of pressure fluid that has passed the pilot valve member 23. Under normal operating conditions both valves are held in the closed position by their respective springs and the main valve by the further action of the fluid pressure acting on the left-hand side of the main piston. When the pressure in the system reaches the blow-off pressure the pilot valve lifts to relieve the pressure on the left-hand side of the main piston and the main valve commences to open against the spring 18. The rate at which the main valve opens is governed by the size of the restricted orifice 32 in the pilot piston through which the fluid on the left-hand side of the piston exhausts, having passed the pilot valve. In another embodiment the pilot valve member is replaced by a hollow rod-like member 51, Fig. 5b, co-operating with a movable seat member 54, and the inlet 57 to the pilot chamber is re-positioned to the side wall. Increase in fluid pressure on the left-hand side of the main piston first moves the seat-valve member combination 54, 51 to the right until the head 56 of the seat member 54 abuts the end of the pilot chamber. Thereafter the valve member 51 is moved further to the right, causing the valve to open and permit fluid to pass to exhaust via the port 58 and orifice 32. An axially movable sleeve 60 may be provided for obturating the port 57 if it is desired to render the valve inoperative. The orifice 32 in either of the above embodiments may be replaced by an electromagnetically-controlled valve which normally gives a restricted flow equivalent to the orifice, but can be opened to allow fuel flow in which condition the valve acts as an orthodox safety valve. Alternatively the valve may be in parallel with the orifice, in which case the valve either increases the area of flow or shuts completely, leaving only the orifice open. The Provisional Specification also describes a fluid-actuated valve (Fig. 3, not shown) comprising a hollow piston having a large outlet opening from its interior and embodying a closure member on its inlet end, the latter also having both a restricted passage and a parallel valve-controlled passage leading to the piston interior; the latter opens when the fluid pressure has attained a value sufficient to unseat the closure member.