Recommended Suction Flow Velocity for Boiling Fluids
Recommended flow velocity for the pump suction side
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Capacity problem, cavitation and high power consumption in a pump, is often the result of the conditions on the suction side. In general - a rule of thumb - is to keep the suction fluid flow speed below the following values:
| Pipe bore | Boiling Liquids | ||
| 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 the cavitation problem - may be extremely difficult to pump. If the pressure at any point within the pump falls below the vapor pressure of the liquid being pumped, vaporization or cavitation will occur. For example, water at 100oF (38oC) will boil or vaporize if exposed to a vacuum of 28-in Hg. The cavitation problem increases with higher temperatures.
More about boiling water or condensate pumping in steam systems can be read here:
- Condensate Pumping The challenge with pumping condensate with
high temperature and cavitations of pump wheels.
- Steam Systems and Feeding Pumps Suction Lift
More about NPSH suction problems can be read here:
- Cavitations and NPSH An introduction to cavitations and Net Positive Suction Head, NPSH
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