Devices Used For Measuring
Pressure Of Fluids
Shuvashis Sen Shuva
Department of Civil Engineering
Mehedi Hasan Melon
Department of Civil Engineering
Dhaka International University
Pressure Measuring Divices
Presure:- It is the force applied perpendicular to the surface of an
object pre unit area over which that force is distributed.
Pressure = force/area
The devices used for measuring the fluid pressure are termed as
pressure measuring devices.
SI Unites : Pascal (N/𝒎𝟐)
Bourdon Tube Pressure Gauge
• The Bourdon Tube Gauga, Invented about 1850, is still one of the most
widely used instruments for measuring the pressure of liquids and gases
of all kinds, including steam, water, and air up to a force of 100,000
pounds per square inch (70,000 Newton’s per square cm).
• The device consists of a flattened circular tube coiled into a circular arc.
One end is soldered to a central block and is open to the fluid whose
pressure is to be measured; the other end is sealed and coupled to the
pointer spindle. when the pressure inside the tube is greater than the
outside pressure, the tube tends to straighten, thus turning the pointer.
The pressure is read on a circular scale.
• Bourdon tubes come in three basic types :-
• Common applications for a bourdon tube include :
i. Gas distribution.
• Bellow-type gauges are used for the measurement of absolute pressure.
They are more sensitive than the bourdon type. It may be used for
measuring pressures up to 40 mm Hg.
• The below are made up of an alloy with high strength and ductility. It
should have very little hysteresis effect. Commonly brass or phosphor
bronze is used for making bellows.
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Working :- The bellow is used in two forms. In one arrangement, pressure is
applied to one side of the bellows and the resulting deflection is
counterbalanced by a spring. This arrangement indicates the gauge pressure. In
the second arrangement, the differential pressure is also indicated.
In this device, one pressure is applied to the inside of one sealed bellow while
the other pressure is applied to the inside of another sealed bellow.
By suitable linkage and calibration of the scale, the pressure difference is
indicated by a pointer on a scale.
Diaphragm Pressure Gauge
• Diaphragm pressure gauges gauge are used to measure gases and
liquids. They cover measuring spans from 10 bar to 40 bar.
• The measuring element consists of one circular diaphragm clamped
between a pair of flanges. The positive or negative pressure acting on
these diaphragms causes the deformation of the measuring element. The
magnitude of the deformation is proportional to the pressure to be
measured, and it is coupled to the pointer mechanism.
Working :- The diaphragm pressure gauge consists of a circular membrane,
made from sheet metal of precise dimensions, which can either be flat or
The diaphragm is a mechanical connection to the transmission mechanism
which will amplify the small deflections of the diaphragm and transfer them to
The process pressure is applied to the lower side of the diaphragm, while the
upper side is at atmospheric pressure. The differential pressure arising across
the diaphragm lifts the diaphragm and the pointer in motion.
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