The Essential Parameters of Pressure Relief Valves

Some essential factors concerned about the operation of hydraulic pressure regulators are its set pressure, cracking pressure, full-flow pressure, pressure-override, closing pressure, overpressure, blowdown, and backpressure. These useful terms are defined in the following sections:

Set Pressure

It is the inlet pressure, under the specified service conditions, at which a PRV is set to open.

Cracking (Opening) Pressure

It is the value of increasing the inlet pressure of a PRV at which there is a measurable lift of its poppet, and there is a continuous discharge of the fluid through it.

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Full-flow Pressure

The pressure at the inlet of a PRV, when it is passing its rated maximum flow, is called the full-flow pressure.

Pressure Override

The difference between the full-flow pressure and the cracking pressure of a PRV is called the pressure-override or the pressure build-up over the set point of the PRV.

Closing Pressure

It is also known as ‘reseat’ pressure. The closing pressure of a PRV is the value of decreasing inlet pressure at which the poppet of the PRV re-establishes a firm contact with the seat.


It is the pressure increase above the set pressure of a PRV, expressed in pressure units or as a percentage.


It is the pressure that exists at the outlet of a PRV as a result of the pressure in the discharge system. It may be subdivided into superimposed and built-up backpressures.

Superimposed Backpressure

This is the backpressure acting on the outlet of a closed PRV. It is the effect of the pressure in the discharge system coming from multiple sources.

Built-Up Backpressure

It is the increase in the pressure in the PRV’s discharge header when the fluid is flowing through the PRV.

Joji Parambath

Author / Trainer

Fluid Power Educational Series Books


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