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The relief valve should be installed between the pump and the pump discharge check valve
A PRV should be installed on the delivery line going to the building. A relief line should be connected back to the water source in case of excess pressure. It is recommended to be installed in case of use of diesel fire pump.
Pumps connected to adjustable-speed drivers such as a diesel engine shall be equipped with a listed relief valve. Required sizes are specified by nfpa20. It is designed to open on runaway diesels, at approximately a 20% increase above the rated speed.
The valve shall be installed between the pump and the pump discharge check valve. The relief valve should be set approximately 10 psi over the shutoff pressure of the pump plus the static suction pressure.
When pumps are driven by electric motors and controlled by a variable speed pressure limiting control driver a main relief valve is required and should be set below the pressure for which the system components are rated.
