How Does Pump Suction Limit the Flow?
One of the claimed advantages of the centrifugal pumps over positive displacement pumps is their ability to operate over a wide range of flow. Since a centrifugal pump operates at the intersection of a pump curve and a system curve, by varying the system curve the operating point of the pump is easily changed: The convenience and simplicity of such flow control by the discharge valve throttling comes at a price, because a pump is thus forced to run either to the left, or to the right, of it’s best efficiency point (BEP). However, the real danger of operating the pump too far off-peak comes from the suction side considerations. Too far to the right – and you are easily risking to run out of the available NPSHA, causing cavitation problems. Too far to the left – flow recirculation at the impeller eye will let itself known through the noise, vibration, and damage. Thus, the flow must be limited on both sides of the BEP: Consider the first limitation – high flow. Centrifugal pump stops pum
