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A turbo pump is a high pressure fluid pump driven by a gas turbine and designed primarily to supply fuel to ram jet and rocket engines. Turbo pumps are generally constructed as linear units with the pump and turbine colocated on a common shaft although geared examples do exist. The pumps used on turbo units are either axial flow types in which low density fluids are involved or the more common centrifugal types used to pump high density fluids. The pump drive functions in the same way as a conventional vehicle turbo with an external gas or steam source driving the turbine. Turbo pumps may feature rotational speeds of 30,000 revolutions per minute (RPM) or more and are exceptionally sensitive, thereby making them difficult to design and manufacture successfully.
The turbo pump concept was born of the need for a high pressure fuel pump for the German V-2 rocket project during the Second World War. The rocket engines required a high pressure fuel source and pressuring the fuel tanks themselves proved to be impractical. The first turbo pumps used on the V-2 project were driven by decomposed hydrogen peroxide and, after a number of failed test flights, successfully drove the V-2 rocket into infamy. Although not exactly a huge moral success story, the V-2 did prove the viability of high speed, turbine driven fluid pumps, and their development progressed apace in the post-war years.
The principle on which turbo pumps are based centers on standard turbine technology. An external source of highly pressurized gas is directed through a set of turbine blades, thereby causing them to rotate rapidly. They, in turn, drive a pump either through a central shaft common to both turbine and pump or via a series of gears. Turbo pumps are fitted with one of two pump types, either the centrifugal or axial flow variant. Each has its own maximum output pressure and flow rate characteristics suitable for different fluid types.
The centrifugal turbo pump types are, for instance, particularly well suited for pumping dense fluids. These pumps consist of a flat disc with a number of curved vanes mounted around the surface area. When fluid is introduced into the center of a rotating pump disc, the vanes force it towards the outside 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 alternating static and rotating blade sets similar in construction to the turbine. Fluid passes through these sets of blades parallel to the shaft axis where pressure is gradually increased until it exits at the front of the pump.
Historically the turbo pump has been exceptionally difficult to design and construct. Commonly encountered problems with these pumps include excessive inlet recirculation, vortex generation, and cavitation. The exceptionally high rotational speeds involved, often in excess of 30,000 RPM, also place enormous physical strain on the pumps and can result in spectacular mechanical failures. The turbo pump, however, still provides the most practical method of delivering high pressure fuel feeds to rocket and ram jet engines.