Why does centrifugal pump not have a relief valve?

Since the pressure inside the centrifugal pump is not as high to damage the system, (as it is due to the centrifugal force imparted by the impeller, which diminishes during impacting on pump casing), that’s why it doesn’t require a relief valve.

What is the difference between centrifugal and positive displacement pumps?

The obvious difference between the two is in the way they operate. As displayed above, centrifugal pumps impart velocity to the liquid, resulting in pressure at the outlet. Positive displacement pumps capture confined amounts of liquid and transfers it from the suction to the discharge port.

Why will you need a relief valve at the discharge point on a reciprocating pump assembly?

The function of a relief valve as a protection device is to limit pump discharge pressure and horsepower to a specified value without generating any valve instabilities and to positively reseat.

What is positive pump?

What is a positive displacement pump? A positive displacement pump provides a constant flow at fixed speed, regardless of changes in pressure. The pump makes the fluid move by trapping a fixed amount and forcing the volume into the discharge pipe.

Is centrifugal pump a positive displacement pump?

A centrifugal pump is categorised as a non-positive displacement pump. Traps a certain amount of liquid and forces it from the suction to the discharge port. Flow rate remains constant as change in pressure.

When starting a positive displacement pump the discharge valve must be?

A positive displacement pump should have a pressure relief valve installed in the discharge line. The relief valve should be the closest valve to the discharge port of the pump and should bypass the discharge line back to the supply tank.

Why positive displacement pumps are used in hydraulic system?

Most pumps used in hydraulic systems are positive-displacement. If the output port were plugged, pressure would increase instantaneously to the point that the pump’s pumping element or its case would fail (probably explode, if the drive shaft did not break first), or the pump’s prime mover would stall.