GB818653A - Aircraft fuel pumps - Google Patents

Abstract

818,653. Centrifugal pumps. NASH ENGINEERING CO. April 15, 1957, No. 1.2220/57. Class 110 (1). [Also in Group XXIX] A self-priming pump unit comprises a centrifugal pump having separate widely spaced intakes for the opposite halves of its double-suction impeller and a common discharge line, a vacuum pump connected separately to each half of the centrifugal pump for independent removal of centrifugally separated air and vapours from the liquid fuel being pumped, a spring-loaded valve which closes the discharge line when the delivery pressure falls below a predetermined value and serving to retain a sealing ring of spinning liquid at the junction of the two halves of the centrifugal pump when the supply of liquid at both intakes fails, a reservoir in which some of the delivered liquid is retained, and means for bleeding liquid from the reservoir and supplying it to the impeller to maintain the sealing ring. The fuel pump shown in Fig. 1 is submerged in an aircraft fuel tank and comprises a doubleentry impeller 24, the two sides of which draw in fuel through respective intakes 34a, 36a. Air and vapour separated centrifugally from the fuel and collecting in annular grooves 38, 44 are drawn off through respective passages 40 and 46, 48, 50 to separate lobes of a double-lobe liquidring pump 22 and discharged, together with liquid, through a passage 52 into a reservoir 53. The air and vapour separate from the liquid within the reservoir 53, which is normally kept full to overflowing by the liquid discharged by pump 22. If one intake, say 34a, becomes uncovered by fuel, as shown, the associated half of the impeller 24 soon empties except for an undischarged revolving ring 90 of liquid which provides a seal between the two halves of the impeller 24 to allow the other half to continue pumping. To ensure the maintenance of the sealing ring 90, the central partition 37 of the impeller 24 extends radially outwards beyond the tips of the impeller blades. If both intakes 34a, 36a become uncovered, both halves of the impeller 24 cease to discharge, and a non-return valve 70 in the discharge pipe closes. Closure of the valve 70 prevents dissipation of the sealing ring 90 and losses from the ring 90 and from the liquid ring of the pump 22 are made good by liquid bled from the reservoir 53 through ducts 92 and 94 respectively, so that pumping can be resumed when one or both of the intakes 34a, 36a become resubmerged. One of the intakes may be provided with a swivel joint 34h, Fig. 1A, so that it can turn towards the top of the tank under negative gravity or inverted flight conditions, and the opening in the top of the reservoir 53 may be provided with a weighted check valve to close it under these conditions. Where the pump shown in Fig. 1 is used as a booster pump to deliver fuel to the intake of a main pump, a by-pass 108, Fig. 3, is connected to the line 58a joining the two pumps at a point downstream of the non-return valve 70a, so that the main pump can draw liquid from an interceptor tank 110 when both intakes of the booster pump are uncovered. A non- return valve 138 opens in response to the suction of the main pump when the valve 70a is closed. The by-pass 108 includes a flexible bellows 118 so that it can swing in any direction to remain submerged in the fuel in the interceptor tank 110 under all flight conditions. The interceptor tank 110, which is desirably in the form of a vertical cylinder, is located within the main fuel tank and receives fuel from the latter through a number of openings closed by pivoted flap valves 146. Specifications 724,652 and 786,705 are referred to.