GB639135A - Improvements in or relating to apparatus for controlling the mass flow of fluids - Google Patents

Abstract

639,135. Pressure gauges. NORMALAIR, Ltd., WIDGERY, W. M., SWAFFIELD, P. J., and FURLONG, O. D. A. C. March 31, 1947, No. 8690. [Class 106 (ii)] [Also in Group XXIX] Apparatus for controlling the mass flow of an elastic fluid such as air, i.e. the flow independent of changes in density or temperature of the fluid, comprises velocity-flow measuring means, applied to a duct traversed by the fluid, incorporating two valves disposed respectively at the entrance to and exit from a pressure cavity furnished with a pressure-sensitive element, one valve being actuated by a bi-metallic thermostat or other temperature-sensitive means; and the other by an absolute pressure capsule or the like. In the diagram shown in Fig. 1, air flowing along a duct b, say from a centrifugal blower to a pressure cabin of an aircraft, has pipes 2, 14 connected thereto at each side of an orifice a. The upstream pipe 2 is connected to a tubular cavity 3 in a metering head casing c incorporating a bimetallic strip 4, secured at its upper end and with its lower end engaging a double-ended piston valve 5, which controls the flow of air from the pipe 2 into a cavity 6. The cavity 6 is separated from an adjacent outlet cavity 13 by a flexible diaphragm 7 engaging an adjusting-screw 15 on a spring-loaded arm 16, the arm 16 being adapted to actuate a motiontransmitting unit 18 which controls electrically a mechanical device for controlling the mass flow of air through the duct b. The cavity 6 is connected by a pipe 8 to a second valve housing f wherein an absolute pressure capsule 10 operates a double piston valve 9 to control the flow of air to the outlet cavity 13 which is connected by the pipe 14 to the duct b below the orifice a. In operation, assuming the temperature of the air flowing through the duct b is constant and the density decreases, the pressure head in the pipe 2 will increase, and the deflecting of the diaphragm 7 would normally be increased to cause the transmitter 18 to record a higher mass flow than is actually passing were it not for the expansion of the capsule 10, due to the decrease in pressure in the surrounding air, operating the valve 9 to increase the flow of air from the cavity 6 to the cavity 13. If the air pressure is fixed and the temperature changes, the valve 5 is moved by the bi-metallic strip 4 to control the flow of air into the cavity 6. The invention may be applied to air control systems as described in Specification 639,119, [Group XXXV]. The motion transmitting device 18 may actuate a butterfly valve provided in the duct b, or a sleeve valve which permits escape of air through orifices in the duct.