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) boils or vaporizes if exposed to a vacuum of 28 in Hg. The problem with cavitation increases with higher temperature.