Suction system NPSH with dissolved gas

NPSH calculations might have to be modified if there are significant amounts of dissolved gas in the pump suction liquid. See Suction System NPSH Available in this handbook for calculations when dissolved gas does not need to be considered. In that case the suction liquid s vapor pressure is a term in the equation. With dissolved gases, the gas saturation pressure is often much higher than the liquid s vapor pressure. 

Penney discusses contemporary methods of addressing dissolved gases and makes recommendations of his own with plant examples. Basically his recommendations are as follows. When mechanical damage is of prime 

Petmey, R. W., Inert Gas in Liquid Mars Pump Performance, Chemical Engineering, July 3, 1978, p. 63. 

When considering a larger impeller to expand a pump s capacity, try to stay within the capacity of the motor. Changing impellers is relatively cheap, but replacing the motor and its associated electrical equipment is expensive. The effects of a larger diameter (d) are approximately as follows  

Lieberman, N. P, Process Design for Reliable Operations, 2nd Ed., Gulf Publishing Co., 1988. 

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