This invention relates generally to improvements in fuel transfer pumps, particularly of the type designed for use in transferring fuel from a fuel tank in an aircraft. More specifically, this invention relates to an improved and simplified fuel transfer pump of the type having an hydraulic motor for rotatably driving a pump impeller, wherein the hydraulic motor and pump are arranged in a compact modular package to include bearing and seal means designed for eliminating risk of potentially catastrophic ignition of fuel vapors during unlimited operation in a depleted tank.
Relatively high flow fuel transfer pumps are generally well known in the aviation industry for use in pumping fuel from a fuel tank. Such fuel pumping applications include, for example, engine feed or in-flight refueling of an aircraft. Moreover, it is sometimes desirable to transfer fuel from one tank to another on an aircraft for purposes of achieving a more uniform distribution of weight during a partial fuel load condition. For this purpose, fuel transfer pumps have been developed and are frequently designed for installation of several such pumps directly into one or more fuel tanks on an aircraft, wherein the pumps are immersed within the fuel under normal conditions.
Concurrently, many such fuel transfer pumps are powered by an electric motor for rotating an impeller immersed in the fuel to pump fuel through an appropriate fuel outlet to another location. Importantly, in fuel transfer pumps of this type, the fuel being pumped has typically been used as a cooling fluid to transfer heat away from mechanical heat-generating pump surfaces such as bearings and the motor, to prevent generation of excessive heat which could otherwise present a potential ignition source in the presence of volatile fuel vapors. Unfortunately, reliance upon the fuel as a cooling fluid results in a pump design susceptible to overheating and possible fuel vapor ignition in the not uncommon event that the pump is operated for any significant period of time with the fuel tank in an empty or nearly empty condition.
In an effort to address and resolve this potentially catastrophic failure mode in fuel-cooled prior art transfer pumps, alternative hydraulic powered transfer pumps have been developed wherein a source of hydraulic fluid under pressure is provided for driving an hydraulic motor coupled to the pump impeller. See, for example, U.S. Pat. No. Re. 35,404. In a fuel transfer pump of this type, hydraulic fluid is available preferably in the form of inherent internal motor leakage for cooling mechanical pump components in a manner reducing or eliminating the potential for overheating during a dry run condition. However, such hydraulically driven pumps have typically been relatively complex in design and require a separate hydraulic motor.
There exists, therefore, a continuing need for further improvements in and to fuel transfer pumps, particularly of the hydraulically driven type, wherein the pump has a simplified compact design configuration and further includes an impeller and related shaft mounting arrangement designed to eliminate heat generation sources which could otherwise contribute to undesirable ignition of fuel vapors. The present invention fulfills these needs and provides further related advantages.