GB958358A - Improved liquid pumping apparatus - Google Patents

Abstract

958,358. Centrifugal pumps; gas turbine plant. DOWTY FUEL SYSTEMS Ltd. Dec. 12, 1960 [Dec. 15, 1959], No. 42657/59. Headings F1C and F1G. [Also in Division G3] A liquid pumping apparatus for delivery of liquid at widely varying pressures and flow rates to an hydraulic load comprises a main pumping and metering unit capable of pumping any desired flow rate of liquid within a lower pressure range, a centrifugal pumping stage, and a valve means having two operative positions in the first of which it connects the main unit output to the load, by-passing the centrifugal pumping stage, and in the second of which it connects the main unit output through the centrifugal pumping stage to the load. A fuel supply system for a gas turbine engine comprises a positive displacement pump 2, Fig. 3, drawing fuel from a tank 1 and supplying it via a flow metering control 3 and a line 4 to a centrifugal pump 13, which delivers the fuel via a line 35 to spill-type burner nozzles 30. At low rates of flow, the fuel flows from line 4 through a non-return valve 36 to the burner spill line 34 and enters the pump 13 at an auxiliary port 31. At high rates of flow, the pressure in line 4 moves a piston valve 37 downwards against the action of a spring 23, allowing fuel to pass to the main inlet 29 of the pump 13. The resultant increased pressure in line 34 closes the valve 36. Instead of operating completely full of liquid, the pump 13 may operate with a ring of liquid surrounding a central core of vapour. In this case, the pressure at the inlet 29 is substantially zero and any pressure developed by the pump 2 is lost as a pressure drop through the valve 37, so that the entire operating pressure is developed by the pump 13. A heat exchanger 27 is used for cooling a liquid, e.g. engine lubricating oil. In a modification, the valve 37 is replaced by a valve acted on by the pressure in the spill line 34. In an alternative embodiment, the burner nozzles are of non-spill type and the auxiliary port 31 is omitted. At low rates of flow, the nozzles are supplied directly from the line 4 and the pump 13 is out of use, and its outlet may be connected to the inlet of the pump 2 so that it runs empty and consumes little power. At high rates of flow, a valve operated by the pressure in the nozzle supply line connects the pump 13 in series with the pump 2. Fig. 4 shows one form of the flow metering control 3. A throttle 52 in the line 4 is adjusted by an external lever 55 through a rack and pinion. The pressures upstream and downstream of the throttle 52 are applied to respective pressure pads 58 and 59, whereby the pressure difference tends to tilt a pivoted lever 63 against the action of a spring 65 so as to vary the escape of fuel from a vent 67 and hence vary the pressure drop across a restriction 49. The resultant variable pressure downstream of the restriction 49 is applied to a piston 44 which actuates a lever 41 which controls the displacement of the pump 2. Alternatively, if the pump 2 is of fixed displacement the pressures upstream and downstream of the restriction are applied to opposite sides of a piston which controls a variable by-pass valve connected across the pump 2. As a further alternative, the positive displacement pump 2 is replaced by a centrifugal pump having a variable throttle controlled by the flow metering control. 3. Reference has been directed by the Comptroller to Specification 842,354.