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Boiling Fluids - Max Suction Flow Velocity

Recommended max suction flow velocity when pumping boiling fluids.

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Capacity problems, cavitation and higher power consumption in pumps, are often the result of the conditions on the suction side of the pumps.

In general - as a rule of thumb - keep the suction fluid flow speed in boiling liquids below the following values:

Pipe boreBoiling Liquid
Max Velocity
1 25 0.3 1
2 50 0.3 1
3 75 0.3 1
4 100 0.3 1
6 150 0.35 1.1
8 200 0.38 1.2
10 250 0.45 1.5
12 300 0.45 1.5

Boiling liquids - due to cavitation - may be extremely difficult to pump. If the pressure at any point within a pump falls below the vapor pressure of the liquid being pumped, vaporization or cavitation will occur. For example, water at 100oF (38oC) boils or vaporizes if exposed to a vacuum of 28 in Hg. The problem with cavitation increases with higher temperatures.

More about boiling water or condensate pumping in steam systems:

More about NPSH suction problems:

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  • Engineering ToolBox, (2003). Boiling Fluids - Max Suction Flow Velocity. [online] Available at: [Accessed Day Mo. Year].

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