All courses › Fluid Mechanics › U-tube manometer

U-tube manometer

A U-tube manometer measures a pressure difference by letting it create a height difference in a fluid column, often mercury because it is very dense and gives a compact setup. The pressure difference is directly proportional to the height difference.

\Delta p = \rho g\,\Delta h

pressure difference from a height difference in the manometer

Symbols

$\Delta h$	height difference between the legs	m
$\rho$	density of the manometer fluid	kg/m³

Example

A mercury manometer ( $\rho = 13.600$ kg/m³) shows $\Delta h = 15$ cm. $\Delta p = 13.600\cdot 9.81\cdot 0.15 \approx 20.0$ kPa.

Mercury is used because its high density gives a short, readable column even at large pressure differences.

Practise hydrostatics for free →

← Hydraulic press · Continuity →

Part of Fluid Mechanics: Hydrostatics.