U-Tube Manometer

The inclined and vertical u-tube manometer is inexpensive and common in differential pressure measurement of pitot, orifices and nozzles

Manometer with Vertical Column Head

The pressure difference can be expressed as:

p_d = γ h (1)

where

p_d = pressure

γ = specific weight

h = liquid height

Example - Differential Pressure Measurement in an Orifice

A water manometer connects the upstream and downstream of an orifice located in an air flow. The difference height of the water column is 10 mm.

The pressure difference head can then be expressed as:

p_d = 9,8 (kN/m³) 10³ (N/kN) 10 (mm) 10^-3 (m/mm) = 98 N/m² (Pa)

where

9,8 (kN/m³) is the specific weight of water in SI-units.

Manometer with Inclined Tube

Common problems when measuring pressure differences in low velocity systems as air ventilation system are the low column heights and satisfying accurately.

Inclining the tube manometer will increase the accurately.

The pressure difference in a inclined tube can be expressed as:

p_d = γ l sin(θ) (1)

where

l = length of column

θ = angle of column relative the horizontal plane

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