Boiling Fluids - Max Suction Flow Velocities
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 bore | Boiling Liquid Max Velocity | ||
|---|---|---|---|
| inches | mm | m/s | ft/s |
| 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:
- Condensate Pumping - the challenge with pumping condensate with high temperature and the cavitation of pump wheels
- Steam Systems and Feeding Pumps Suction Lift
More about NPSH suction problems:
- Cavitation and NPSH - an introduction to cavitation and Net Positive Suction Head NPSH
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