Inducer (pump component)


An inducer is the axial inlet portion of a centrifugal pump rotor, the function of which is to raise the inlet head by an amount sufficient to prevent significant cavitation in the following pump stage. It is used in applications in which the inlet pressure of a pump is close to the vapor pressure of the pumped liquid. Inducers are virtually always included in the turbopumps for liquid propellant rocket engines, although they are also used in other applications which require high suction performance.

Design parameters

Inducers are meant to increase the suction performance of a pump to the point that little to no cavitation occurs in its impeller. The key performance metrics of an inducer is its suction specific speed Nss and its flow coefficient Φ.
is the imperial version, common in US literature. is the dimensionless version, but is not yet commonly seen in pump literature. Development of an inducer design typically starts with defining the target Nss. A higher value reduces the NPSHR, which reduces the required tank pressures. The consequence of increasing Nss is that it requires a smaller flow coefficient ; which necessitates either a reduction in flowrate, an overall larger/heavier inducer, and/or a faster shaft speed.

Brumfield criterion

There is a direct tradeoff between suction performance and flow coefficient as described by the Brumfield criterion:

Use in rocketry

In order to achieve high delta-v, the structural mass of a launch vehicle should be as low as possible. Liquid fuel tanks can be constructed lighter if the pressure within those tanks is kept low. Typically, for pump-fed rocket engines, the propellant tank pressures are 1/10 to 1/40 of those in a pressure-fed rocket. The structural weight constraint also makes the rotating speed of the turbopump rotor as high as possible. For example, the rotating speed of the oxygen turbopump of the Japanese LE-7 rocket engine is 18300rpm. These two factors above combine to make the pump impeller very susceptible to cavitation. If cavitation occurs in the impeller, the performance of the pump will be severely degraded and the pump itself may be damaged.

Industry examples