Difficulties in adapting centrifugal pumps for use as fuel pumps for turbine powered aircraft are avoided in a system including a centrifugal volute pump (22) on a common shaft (18) with a regenerative pump (24). A pressure responsive throttling valve (46) is connected to the inlet (50) of the regenerative pump (24) so as to cause the regenerative pump (24) to provide fuel at a desired, substantially constant pressure while a check valve (80) is connected to the outlet (72) of the centrifugal volute pump (22) to allow flow from the volute (72) but not the reverse. The outlet side of the check valve (80) can also be selectively connected to the outlet (84) of the regenerative pump (24) so that when the pumps are rotating relatively slowly, the regenerative pump (24) will pump fuel at the desired, substantially constant pressure and, as rotational speed increases, the check valve (80) will open when the centrifugal volute pump (22) is pumping fuel at or about the desired substantially constant pressure.
A pumping system for selectively activating the stages of a multi-stage centrifugal pump is provided. The pumping system has a first stage impeller for receiving fluid into the system and imparting rotational energy into the fluid. The system also has a second stage impeller for centrifugally imparting additional rotational energy into the fluid after the first stage impeller. A valve selectively closes an inlet to the second stage impeller so that the system operates as a single stage centrifugal pump while the second stage impeller remains wetted.
A fluid flow system for a gas turbine engine provides combustion fuel to a main pump and an actuator pump significantly reducing heat generation at low flow demand, while regulating actuator flow temperature at high flow demand. Fuel flow from the actuator pump in excess of the actuators needs is directed through an actuator minimum pressure valve and into a thermal bypass valve (TBV.) Depending upon the temperature of the fuel, the TBV determines the path of the excess actuator pump fluid flow. The TBV divides the fuel flow between being recirculated to the actuator pump inlet and the main pump output flow path to the engine fuel input conduit. The engine actuators are thereby assured of receiving flow which preclude freezing of water entrained in the fuel. When there is minimal concern with the possibility of freezing water entrained in the fuel, the TBV passes a greater percentage of fuel through to join together in the engine fuel input conduit.
