Pressure Measurement · Glossary

What is Accumulation?

% above MAWPPressure Measurement

Accumulation is the pressure rise above the MAWP of the protected equipment while the relief valve is discharging.

Accumulation Explained

A relief valve needs some pressure rise above set to reach full lift and rated capacity. The code limits how high the vessel pressure may go during relief: this is the allowable accumulation.

Overpressure is the related rise above set pressure. When the set pressure equals MAWP, overpressure and accumulation are the same.

Accumulation: Typical Values

Single valve, non fire	10 % or 3 psi, whichever is greater
Multiple valves	16 % or 4 psi
Fire case	21 %

Calculators for Accumulation

CalculatorRelief Valve Sizing Calculator for GasFree online calculator with formula and worked example.CalculatorLiquid Relief Valve Sizing CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is Accumulation?

Accumulation is the pressure rise above the MAWP of the protected equipment while the relief valve is discharging.

Is relieving pressure the same as accumulation?

No. Relieving pressure is set pressure plus overpressure, used to size the valve; accumulation is the rise above MAWP.

Why is fire case allowed more?

Fire is a rare emergency, so codes accept a higher temporary pressure to keep relief valve sizes practical.

Learn more on the blog

Instrumentation and control standards

A practical guide on instrumentationblog.in with more detail on accumulation and how it is applied on real plants.

Read Full Article

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