fixing an inducer to combat cavitation in pump

[Rotaryeqpt]

Dear Forum Members
I understand that an eqpt/device fitted in the suction side of a pump can effectively handle cavitation/insuffient NPSH.
Can any one explain about Inducer?

Thank you,

 

[flowman]

Rotaryeqpt,
An inducer stage is designed for very low npshr, it basically feeds the npshr of the stages above it. It is an invalueable tool when the npsha is low such as a condensate pump. It also allows you to shorten condensate pump and barrel. Johnston's Q-model's are inducers I'm not aware of other inducer MFR'S.

Goodluck, Flowman

 

[vanstoja]

The following is from the Pump Handbook 1976 Edition pg.2-12,
"Should the available NPSH be so low that the required suction specific speed is above about 18,000, then a separate axial flow impeller of special design - an inducer - is used ahead of the centrifugal impeller. Its flow angle is typically between 5 and 10 degrees. The vane angle is about 3 to 5 degrees larger. The number of vanes is often only two, and not more than four. The vane thickness is made as small as possible."

 

[25362]

One type of mechanical inducers in centrifugal pumps is a kind of axial flow (screw type) impeller attached to the pumps' impeller rotating together with it. It acts, in fact, as a booster pump to the first -or single- stage of a pump. It requires less NPSH and it is there to increase the suction head of the given pump.

The discharge pressure of the pump with inducer doesn't change at large flow rates. At lower flow rates towards shutoff the head rises a bit, and pumps with flat or drooping characteristic curves may have a shape uplift making these a bit more steep and amenable to some users.

Since it causes prerotation a careful match between inducer and suction impeller is required.

 

[vanstoja]

A good review of experimental and analytical investigations of inducer fluid dynamics that lists 113 references is:

Lakshminarayana,B.(1982), "Fluid Dynamics of Inducers - A Review, Trans. ASME, J. of Fluids Engineering, Vol. 104, December, pp.411-427

This may be obtainable from the ASME Library.