GB1393242A - Fluid flow control devices - Google Patents

Abstract

1393242 Valves, fluid pressure brakes DUNLOP Ltd 17 April 1972 [16 Jan 1971] 2205/71 Headings F2V and F2F [Also in Division G3] A fluid control device comprises a spool member 74, Fig. 3, located in a bore 75 in a housing. The spool controls a pair of variable spill ports B, D each receiving pressure fluid from respective inlets 79, 81 having fixed restrictors A, C therein and connected to input pressure P1, P3. The aperture areas and discharge coefficients are equal for the fixed restrictors, and for the variable spill ports for all positions of the spool. One end of the spool is subjected to static pressure P2 and the other end is subjected to pressure PX on the downstream side of restrictor A. Thus when PX = P2, Spill ports B, D and fixed ports A, C are of the turbulent type. An alternative embodiment, Fig. 4 (not shown), incorporates laminar spill and fixed restrictions. The device performs combined muliplication and division of three variables but instead the pressures supplied may be any combination of fixed and variable pressures, providing P2<P1. Thus with P1 constant, multiplication of two variables (P2.P3) can be performed, or with P2 or P3 constant, division of two variables is possible. If both P2 and P3 are constants then the reciprocal of a variable can be found. With P1 and P3 at constant values, variable input P2 will be amplified by the ratio of the constant values. By interconnecting P2 and P3, P4 becomes equal to and P1 may be made constant, or by interconnecting P4 and P1, P4 becomes equal to #P2.P3 and P2 or P3 may be made constant. Applications of the device include fuel metering circuits of aircraft gas turbine engines, wherein the fuel consumption is controlled in accordance with, e.g. height, air temperature, fuel temperature and engine speed; brake controls for skid prevention, the output pressure of the device being supplied as the brake-applying hydraulic pressure and input pressure being derived from a skid sensor such as a wheel-driven pump; and control of selector valves by providing an overcompensated amplifier biased to one position and utilizing pulse inputs which cause it to move to full or zero output.