GB711227A - Improvements in liquid dispensing systems - Google Patents

Abstract

711,227. Fluid-pressure servomotor-control systems. SHELL REFINING & MARKETING CO., Ltd. July 18, 1952 [July 31, 1951], No. 18073/51. Class 135 A liquid dispensing system, e.g. an aircraft fuelling system, comprises a pump 1, Fig. 1, a delivery line 5 connecting the discharge s'de 4 of the pump to at least one dispensing point controlled by a valve 8 and containing a non-return valve 6 permitting flow from the pump, and a bye-pass line between the discharge and suction sides of the pump and controlled by a valve 13. This valve varies the flow through the bye-pass in accordance with the pressure at a point 11 between the valve 6 and the dispensing point or points. The pressure is that at the throat of a Venturi 7 and actuates a pilot valve member 44, Fig. 2, controlling a piston 22 connected to the bye-pass valve closure member 17. Pump discharge and suction are connected to chamber 23, 24, respectively on opposite sides of valve seat 20. With the pilot valve closed, the pressure in chamber 23 holds member 17 seated due to the piston 22 being larger than the member. When the pressure at point 11, acting on a piston 43, overcomes a spring 33 the pilot valve opens to admit pressure liquid through ports 46, 47 to the rear of piston 22 to unseat member 17. If flow through the Venturi ceases due to closure of all valves 8, the pressure becomes sufficient to move piston out of bore 39 whereupon the pressure acts on an addition piston 42 to urge the valve member 44 against stop 34 and member 17 moves to fully open position against a stop 25. Due to the additional area of piston 42, the pilot valve will not close until the pressure at point 11 drops below the initial opening pressure. On closure of the pilot valve, the liquid behind the piston 22 bleeds off through a bore 28 in the piston and member 17 to permit the member 17 to be seated. The liquid entering the chamber 35 containing piston 42 leaks away through bores 49, 50 in the member 44 and a port 45. A pressure storage vessel 14 in line 5 compensates for any leakage which may occur when all valves 8 are closed.