What is Back Pressure?
Back pressure is the pressure at the outlet of a relief valve, from the discharge system or from flow through it.
Back Pressure Explained
Superimposed back pressure exists before the valve opens, for example from a flare header. Built up back pressure develops in the outlet piping once the valve flows.
High or variable back pressure changes the opening point and capacity of a conventional valve. Balanced bellows or pilot operated valves are used where it is significant.
Back Pressure: Typical Values
| Conventional valve, built up back pressure (API 520) | usually limited to 10 % of set pressure at 10 % overpressure |
Calculators for Back Pressure
Frequently Asked Questions
What is Back Pressure?
Back pressure is the pressure at the outlet of a relief valve, from the discharge system or from flow through it.
Why does back pressure matter?
It acts on the disc and can raise the opening pressure of a conventional valve or cut its capacity.
What does a balanced bellows do?
It shields the disc from back pressure so the set pressure is not affected by it.
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Instrumentation and control standards
A practical guide on instrumentationblog.in with more detail on back pressure and how it is applied on real plants.
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