Pressure Measurement · Glossary

What is a Manometer?

liquid column gaugePressure Measurement

A manometer measures pressure from the height difference of a liquid column in a U tube or inclined tube.

Manometer Explained

Pressure applied to one leg pushes the liquid down on that side and up on the other. The height difference, times liquid density and g, gives the pressure difference.

Manometers are simple and fundamentally accurate, and are still used for low pressures, draft and as calibration references. Inclined tubes spread the scale for very low pressures.

Manometer Formula

Δp = (ρ_m − ρ_f) × g × h

ρ_m	manometer liquid density
ρ_f	density of the fluid above it (≈ 0 for air)
h	height difference (m)

Example: A 100 mm water column with air above: Δp ≈ 1000 × 9.80665 × 0.1 = 981 Pa, about 9.8 mbar.

Calculators for Manometer

CalculatorManometer CalculatorFree online calculator with formula and worked example.CalculatorHydrostatic Pressure CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is a Manometer?

A manometer measures pressure from the height difference of a liquid column in a U tube or inclined tube.

Why read the meniscus carefully?

Water curves up and mercury curves down; read at the bottom or top of the curve consistently, at eye level.

Why is the fluid density subtracted?

The process fluid above the manometer liquid also has weight; for gases it is negligible, for liquids it is not.

Learn more on the blog

Pressure gauge calibration procedure

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

Read Full Article

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