Inducer

INDUCER I011

A small low head, axial flow impeller that attaches to the conventional impeller of a centrifugal pump to increase the pump’s suction head (pressure), and prevent cavitation problems.

 

The main purpose of the inducer is not to generate an appreciable portion of the total pump head, but to increase the suction pressure of a conventional impeller. They reduce NPSH required and permit the pump to run at a higher speed, with a given NPSH available.

  • Most centrifugal pump impellers have a SSS (suction specific speed) number of 8,000 to 12,000.The use of an inducer can increase this number to a range of 15,000 to 35,000. This will allow lower flow pumps to operate at 11,000 rpm with the same NPSH, which would be required at 3600 rpm, without the inducer.
  • The inducer flow angle is some where between five and ten degrees with typically two vanes and no more than four. Inducers have been used successfully with suction specific speed numbers of approximately 24,000 (14,700 metric).
  • Cavitation damage of inducer blades may occur above certain experience-established inducer tip speeds.
    • At lower tip speeds, cavitation will not produce damage regardless of SSS value. Allowable tip speed is also a function of inducer materials; e.g., titanium alloy is 20 percent higher than for stainless steel. Tip speeds may also be increased for lower specific gravity liquids.
  • Inducer flow range must be designed and selected to provide sufficient SSS over the intended operating range to avoid cavitation in the main impeller.
    • Suction specific speed typically is reduced at low and high ends of inducer performance range
  • An inducer should be specified any time the calculated suction specific speed number is above 18,000 in USCS units or 11,000 in SI units. The inducer will reduce the NPSHR of the pump or permit the pump to run at a higher speed.
  • The inducer flow angle is some where between five and ten degrees with typically two vanes and no more than four. Inducers have been used successfully with suction specific speed numbers of approximately 24,000 (14,700 metric).
  • Although the efficiency of the inducer is low, it will not reduce the pump overall efficiency significantly.

Not all pump manufacturers have this feature available

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Posted

  • On February 16, 2018