What would be the result of throttling the suction valve to the point where the flow was less than that recommended by a centrifugal pump? The designed total net head would be reduced. The pump would begin to cavitate.
• Effect of throttling a suction valve vs a discharge valve on a centrifugal pump • Relationship between flow rate and total dynamic (net) head on a pump performance curve • Conditions that promote cavitation: NPSH available vs NPSH required
• Think about what happens inside a centrifugal pump if you restrict the flow on the suction side: does pressure at the eye of the impeller increase or decrease? • Look at a typical centrifugal pump curve: when you move to a lower flow rate, what normally happens to the developed head? • Ask yourself: does cavitation usually get worse when you starve the pump of suction pressure, or when you throttle on the discharge side?
• Confirm whether throttling on the suction side increases or reduces the NPSH available (Net Positive Suction Head). • Check from a standard pump characteristic curve how head changes as flow decreases at constant speed. • Verify whether cavitation is more likely when suction pressure is low and flow into the impeller eye is restricted.
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