The cavitation head issue of 90°C hot water pumps
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The issue of net positive suction head available for 90°C hot water pumps: In a tank at atmospheric pressure, when the 90°C hot water is at a low level (for example, at the same height as the pump inlet), and the pump is designed with an NPSHr of 2.89 meters, can this pump still be used?
In practice, it can’t be used; theoretically, if friction is ignored, it can just barely be used.
The saturated vapor pressure of water at 90°C is 70.1 Kpa. In a plain environment with an atmospheric pressure of 101.3 Kpa, the net positive suction head is 2.89 m; adding a safety margin of 0.5 m makes the situation quite precarious. Even if it can run, cavitation is inevitable.
It won’t work; it’s at the critical cavitation condition
Using a water ejector at the pump inlet, as specified, can slightly increase the inlet pressure and thus prevent cavitation.
Based on the current situation, it cannot be used; there is a high likelihood of the pump running dry. However, adding an elbow to the tank can reduce the height of the inlet pipe.