What happened when Delivery valve closed and Suction valve open in centrifugal pump.(in running conditions)

Answer Posted / phani

After some period, churning effect will takes place, which means dry run. This is due to continuous water circulation within the casing. After some period, due to friction between pump casing and flowing water, heat will be generated, slowly water getting heated up and further evaporation takes place, then pump will be under dry run condition.
Internal circulation means, discharged water can't escape from casing, so only the way to escape is passes through wear ring clearance and came to suction, again from suction to discharge water will flow.

Due to this dry run, shaft and casing will be over heated and thermal expansion takes place, shaft may brake at time.

If bluish or burning marks are found on shaft/impeller, it means that "pump runs on shut off head or Churning effect", it is confirm.

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