GB1009494A - Improvements in relief valve mechanisms - Google Patents

Abstract

1,009,494. Valves. HYDRAULIC UNIT SPECIALTIES CO. Aug. 2, 1962, No. 29756/62. Heading F2V. [Also in Division G3] A valve for relieving abnormally high or low pressures in a fluid system comprises a main poppet valve 14 controlling a by-pass passage 9 between a system conduit 6 and a drain conduit 8. The valve poppet 14 is hollow and slidable over a fixed body part 16 to form a pressure chamber 52 freely connected by annular passage 50 to a chamber 52<SP>1</SP>. The chamber 52 is normally in communication with the conduit 6 by a through passage 55 in a tube 53 which loosely fits in a bore 54 in the valve poppet. The chamber 52 has a vent outlet controlled by a pilot poppet valve 25 which, when open, connects the chamber to the drain 8 by an axial bore in the body part 16, parts 45, and annular passages 44, 48, which allow free flow of the fluid. The pilot poppet valve 25 carries a disc 28 and a light spring 56 acts in a closing direction on the main poppet 14. In operation, the pressure in chambers 52 and 52<SP>1</SP> is equal to that in line 6 under normal conditions and acts to hold the main valve 14 closed against the action of the fluid pressure acting in passage 9 on the end face of the valve 14. When the pressure reaches a predetermined value, the pilot poppet 25 opens to vent chamber 52, 52<SP>1</SP> and the main valve 14 opens under the action of the pressure in the passage 9. At the same time, this pressure acting on the tube 53 moves the tube to engage the disc 28 of the pilot poppet. This movement provides that the pilot poppet is held open and the flow through the tube to the chambers 52, 52<SP>1</SP> from conduit 6 is restricted. Restricted flow will take place due to the loose fit of the tube in the bore 54. When the pressure in conduit 6 drops sufficiently to allow the pilot poppet valve 25 to close under the action of spring 33, the pressure in chambers 52, 52<SP>1</SP> again rise to that in the conduit 6 to close the main valve poppet 14. In the event of the pressure in the conduit 6 dropping below that in the drain conduit 8, which is at atmospheric pressure or slightly above, the main valve 14 opens to allow flow from the drain conduit 8 to the system conduit 6. This is achieved by a surface 47 on the main poppet 14 which is subjected to pressure in the drain conduit 8. Specifications 950,131 and 985,950 are referred to.