The Check Valve is present to prevent any backflow through the pump.
When the pump is pumping, it delivers liquid from low pressure (suction) to high pressure (discharge side). If the pump trips due to any reason, there is a driving force for the liquid to flow from the discharge piping (high pressure area) into the suction piping (low pressure area) through the pump casing, which will 1. Damage the pump and 2. May overpressurise the upstream piping/components/vessels which are not designed for the high pressure.

So, to prevent the backflow through the pump, Check Valve is installed just after the pump discharge.

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