Relief Valve

This depends on what type of pump it is, and what other valves or flow restrictions may exist in the pump discharge line.

For a positive-displacement pump (screw, vane, gear, piston, and some other types), any blockage in the discharge could result in motor overload, sudden overpressure, vane or other component breakage, or pipe rupture. These possibilities can be protected against by a relief valve that vents back to pump suction, to the source vessel, or to atmosphere.

Centrifugal or axial propeller pumps do not typically have this problem, because they have inherent maximum pressures. However, if the discharge is blocked, the pump will "churn" on the fluid, increasing its temperature. In this case, a small bypass line from the pump discharge back to the source vessel can protect the pump. In refrigeration practice, for instance, a "Q-min" orifice is commonly used.

GA Tornado... thanks for the insight @ "Q-min".

thanks for the reply

Relief valves are sometimes used for flow control (or even other purposes), a practice not encouraged by pump manufacturers.

For the same reason it is used anywhere else:

• to ensure that over-pressure cannot occur.