Submergence flow control to prevent cavitation


Submergence control is sometimes used in applications where NPSH Available to the pump is limited and the pump would naturally be operating with marginal NPSH.  A good example is condensate pumps in steam power systems.

Condensate pumps take condensed steam from the bottom of the steam condenser (hotwell).

  • Ideally, when operating at the design conditions, the liquid level in the condenser hotwell provides sufficient NPSH to the pump so that it operates on the head curve, producing the design rate of flow

When the load on the electric generator is reduced, the steam required is reduced and the amount of condensed steam entering the condenser hotwell is reduced.

  • This reduction in condensate causes the pump to draw down the level of liquid in the condenser, thereby reducing the NPSH available to the pump.
  • The reduction of NPSH available to the pump causes it to cavitate, resulting in a reduction in the rate of flow.
  • If the load on the generator does not change, the pump will operate in this mode until the load is increased back to normal.
  • The continuous cavitation in the impeller can be damaging to the pump.