Level Measurement · Glossary

What is Vessel Holdup Time?

minutes between levelsLevel Measurement

Vessel holdup time is how long the volume between two levels lasts at a given flow, used to set alarm and trip levels.

Vessel Holdup Time Explained

Holdup time between normal and low level gives operators time to respond to an alarm before a trip. Between low and low low level it protects pumps from running dry.

Process designers specify holdup and surge times; instrument engineers set alarm and trip points to match.

Vessel Holdup Time Formula

t = V ÷ Q

V	volume between the two levels
Q	net flow in or out

Example: 10 m³ between levels at 20 m³/h gives 0.5 h, or 30 minutes.

Calculators for Vessel Holdup Time

CalculatorVessel Holdup Time CalculatorFree online calculator with formula and worked example.CalculatorSump Pump Cycle Time CalculatorFree online calculator with formula and worked example.CalculatorLevel Rate to Flow CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is Vessel Holdup Time?

Vessel holdup time is how long the volume between two levels lasts at a given flow, used to set alarm and trip levels.

How is holdup time used for alarms?

The time between an alarm and the trip must exceed the time operators need to act.

Is surge time the same?

Surge time usually refers to the volume available to absorb flow upsets; definitions vary by company.

Learn more on the blog

Basics of level measurement

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

Read Full Article

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