GB950131A - - Google Patents

Abstract

950,131. Valves. HYDRAULIC UNIT SPECIALTIES CO. Dec. 1, 1961 [Dec. 1, 1960; Nov. 6, 1961 ; Nov. 17, 1961], No. 43153/61. Heading F2V. [Also in Division G3] A flow control valve for relieving both high and low pressures comprises a valve housing 18 having a supply line port 24 and a reservoir port 25, the flow between which is controlled by a valve closure 23 co-operating with a seat 19. The valve closure is formed on the end of a main poppet member 21 having a piston portion 26, loaded by a spring 22, slidable in a cylinder 20 and forming a pressure chamber 55. The pressure in the chamber 55 is normally maintained substantially equal with that at the port 24 by means of plunger member 59 formed with a longitudinal bore 63 whose end co-operates with a ball check valve 60 such that flow from port 24 to the chamber is restricted by a throttle passage 59 while flow from the chamber to the port opens the ball valve to provide free flow. A spring loaded pilot valve 36 controls flow from the chamber 55 to exhaust. In operation as the pressure at the port 24 rises so will that in the chamber 55 rise until the pressure reaches a predetermined value to open the pilot valve 36. Fluid flows freely from the chamber 55 to exhaust and the pressure at port 24 acts to open the valve 23 to allow flow from port 24 to the port 25. The increased pressure in port 24 to that in chamber 55, due to the throttle, acts to move the plunger 59 which holds the pilot valve open until the pressure at port 24 falls to a value at which the spring 38 closes the pilot valve. Fluid then flowing to chamber 55 balances the pressure at the port 24 and the spring 22 closes the valve 23. When the fluid pressure in port 24 falls fluid flows from chamber 55 freely past the ball 60 and when the pressure in chamber 55 falls below a predetermined value, the pressure in port 25 acting on the area 56 of the piston 26 opens the valve to allow flow from the port 25 to the port 24. This increase in pressure acts on the plunger 59 to move it into abutment with the pilot valve. Such movement increases, by its displacement, the pressures in the chamber 55 to bring this pressure rapidly to a value at which the valve 23 again closes and as flow takes place past the throttle portion of the plunger 59, the plunger gradually assumes the position shown. In a modification the plunger 59 and ball 60 are replaced by a cylindrical piston element which may be lightly loaded and the passage to the chamber 55 is partially oblique to the axis whereby movement of the plunger provides throttling or free flow under the above conditions. The flow past the pilot valve may take place to the port 25. In a further modification the main valve is formed as two valve members having inner and outer members of which one is seated on the other, the inner valve moves to relieve excess pressure at port 24 while they both move to relieve negative pressure at this port.