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Turbopumps are high-pressure fluid pumps driven by gas turbines, used to supply fuel to rocket and air-jet engines. They are difficult to design and manufacture due to their sensitivity and high rotational speeds. The concept was born out of the need for a high-pressure fuel pump for the German V-2 rocket project during World War II. Turbo pumps are equipped with either centrifugal or axial flow pumps, suitable for different types of fluids. Despite challenges, turbopumps remain the most practical method of supplying high-pressure fuel feeds to rocket and propulsion engines.
A turbopump is a high-pressure fluid pump driven by a gas turbine and designed primarily to supply fuel to rocket and air-jet engines. Turbo pumps are generally built as linear units with the pump and turbine positioned on a common shaft, although examples of gears do exist. The pumps used in turbo units are either the axial flow type involving low density fluids or the more common centrifugal types used to pump high density fluids. The pump drive works in the same way as a conventional vehicle turbo with an external source of gas or steam driving the turbine. Turbo pumps can have rotational speeds of 30,000 revolutions per minute (RPM) or more and are exceptionally sensitive, making them difficult to successfully design and manufacture.
The turbo pump concept was born out of the need for a high pressure fuel pump for the German V-2 rocket project during World War II. The rocket motors required a high-pressure fuel source, and the pressure from the fuel tanks themselves proved impractical. The first turbo pumps used in the V-2 project were powered by decomposed hydrogen peroxide and, after several failed test flights, successfully brought the V-2 rocket to infamy. Though not exactly a great moral success story, the V-2 demonstrated the feasibility of high-speed, turbine-driven fluid pumps, and its development progressed rapidly in the postwar years.
The principle on which turbopumps are based is centered on standard turbine technology. An external source of highly pressurized gas is directed through a set of turbine blades, causing them to spin rapidly. They, in turn, drive a pump through a central shaft common to both the turbine and the pump, or through a series of gears. Turbo pumps are equipped with one of two types of pump, either the centrifugal or axial flow variant. Each has its own maximum outlet pressure and flow characteristics suitable for different types of fluids.
Turbo centrifugal types of pumps are, for example, particularly suitable for pumping dense fluids. These bombs consist of a flat disk with several curved vanes mounted around the surface area. When fluid is introduced into the center of a rotating pump disc, vanes force it out of the pump and through the outlet at high velocity. Axial flow pumps, on the other hand, are better suited to low-density fluids and consist of sets of alternating static and rotating blades similar in construction to the turbine. The fluid passes through these sets of blades parallel to the shaft axis where the pressure gradually increases until it exits the front of the pump.
Historically, the turbopump has been exceptionally difficult to design and build. Problems commonly encountered with these pumps include excessive inlet recirculation, vortexing, and cavitation. The exceptionally high rotational speeds involved, often in excess of 30,000 RPM, also place enormous physical stress on the pumps and can lead to spectacular mechanical failures. However, the turbopump still provides the most practical method of supplying high-pressure fuel feeds to rocket and propulsion engines.
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