Bourdon Tube Pressure Gauge

Pressure measurement is the analysis of an applied force by a fluid (liquid or gas) on a surface. Pressure is typically measured in units of force per unit of surface area. Many techniques have been developed for the measurement of pressure and vacuum. Instruments used to measure and display pressure in an integral unit are called pressure gauges or vacuum gauges. Bourdon gauge is a mechanical device, which both measures and indicates and is probably the best known type of gauge.

The Bourdon pressure gauge uses the principle that a flattened tube tends to straighten or regain its circular form in cross-section when pressurized. This change in cross-section may be hardly noticeable, involving moderate stresses within the elastic range of easily workable materials. The strain of the material of the tube is magnified by forming the tube into a C shape or even a helix, such that the entire tube tends to straighten out or uncoil elastically as it is pressurized. Eugène Bourdon patented his gauge in France in 1849, and it was widely adopted because of its superior sensitivity, linearity, and accuracy; that’s where the name is derived from.

A vacuum gauge is a pressure gauge used to measure pressures lower than the ambient atmospheric pressure, which is set as the zero point, in negative values (e.g.: −15 psig or −760 mmHg equals total vacuum). Most gauges measure pressure relative to atmospheric pressure as the zero point, so this form of reading is simply referred to as "gauge pressure". However, anything greater than total vacuum is technically a form of pressure. For very accurate readings, especially at very low pressures, a gauge that uses total vacuum as the zero point may be used, giving pressure readings in an absolute scale.

In practice, a flattened thin-wall, closed-end tube is connected at the hollow end to a fixed pipe containing the fluid pressure to be measured. As the pressure increases, the closed end moves in an arc, and this motion is converted into the rotation of a (segment of a) gear by a connecting link that is usually adjustable. A small-diameter pinion gear is on the pointer shaft, so the motion is magnified further by the gear ratio. The positioning of the indicator card behind the pointer, the initial pointer shaft position, the linkage length and initial position, all provide means to calibrate the pointer to indicate the desired range of pressure for variations in the behaviour of the Bourdon tube itself. Differential pressure can be measured by gauges containing two different Bourdon tubes, with connecting linkages.

Bourdon tubes measure gauge pressure, relative to ambient atmospheric pressure. When the whole gauge is subject to mechanical vibration, the entire case including the pointer and indicator card can be filled with an oil or glycerine.

Gauges manufactured in the Pressure Gauge Division of Goa Thermostatic provide an accuracy of ±1% of span. In the Pressure gauge division of Goa Thermostatic, we manufacture Bourdon sensing Pressure gauges which can measure upto 1000 Bar or 1000 kg/cm2 and compound or vacuum gauges from -100/2400 Bar or -100/2400 kg/cm2 or 30inch/300 psi.

Refer TABLES for ranges available, connection types and the various options available with the supply of Temperature gauges.

  • "All Stainless Steel" fully welded construction.
  • Weather-proof casing to IP:65, IS:13947.
  • Shatter-proof glass as a standard.
  • Micro-gear pointer for zero re-set.
  • Blow out disc at the rear of the case.
  • Dry and Liquid Filled versions.
Scope of supply : PG 100 Series Bourdon sensing Pressure gauges, ”Socket welded to case construction” with no external mounting screws.
Model Number (Typ) : PG 100 Series P-B-B-1-4-S4-S6-S4-S4-0/16-3N-Op0.
Design : EN-837-1.
Case : SS304, Weather-proof to IP:65, IS:13947, bayonet bezel ring.
Dial Size : 100mm(4”), white background with black numerals.
Mounting : Bottom entry, local mounting.
Bourdon : SS316, TIG welded to socket and stress relieved.
Socket : SS316.
Movement : SS304.
Pointer : Micro-gear adjustment type for zero re-set.
Window : Shatter-proof Glass.
Range : As shown against tag nos in kg/cm2.
Overall inaccuracy : Within ± 1% FSD.
Over range protection : 130% FSD.
Blow Out Disc : Neoprene rubber, provided at the back of the case.
Connection to process : 3N…½”NPT(M), bottom entry.
Option1 : Snubber in SS304, floating pin and orifice design, end connections ½”NPT (M)x(F).
Option2 : Pig tail syphon in SS304, end connections ½”NPT(M) x (F).
Option3 : 2 way isolation valve with drain plug in SS304, needle valve, end connections ½”NPT(F) x (F).
Option4 : Gauge saver, end connections ½”NPT(M)x(F).
Option5 : Safety Pattern design with Solid Front and blow out back.


1) For high pressure applications, we can offer “Safety Pattern” gauges with “Solid Front” partition between sensing bourdon and dial and “Blow out back” for quick pressure relief in the unlikely event of bourdon failing due to sudden overpressure. This feature is a Safety feature and would prevent possible injury to operators.

*Please note the following parameters can be varied by referring to the model decoding sheet:
Model Number, Case material, Dial Size, Mounting, Bourdon and Socket Material, Range and unit of measurement required, Accuracy required, and the Connection to process.


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