Bourdon Pressure Gauge
A Bourdon gauge is a mechanical device used to measure and display a system pressure. The gauge can be used for measuring pressure in both gas and liquid state systems.
Design and Operation
The heart of the Bourdon gauge is the Bourdon tube. The tube is manufactured in a semi-circular (C-shape), or, coiled shape. The tube is open to atmosphere at one end and sealed closed at the other. Any increase in system pressure within the tube causes the tube to expand and straighten, the change is small but magnified due to the shape of the tube. The change in C-shape or coil radius is transferred to the indicator needle and this movement allows personnel to visually view the pressure within the system.
Gauge or Absolute Pressure?
Bourdon pressure gauges measure the gauge pressure relative to the atmospheric pressure, this means that the pressure shown may increase or decrease depending upon elevation (so a system pressure at the top of a mountain is displayed differently to that at the bottom!). For example, the gauge pressure at sea level (where atmospheric pressure is the highest) will be lower that the gauge pressure at higher altitudes.
A system pressure that is displayed without reference to ambient conditions is called an 'absolute' pressure.; gauge pressure is often written with the numeral gauge pressure followed by a '(g)' e.g. 10 bar(g).
Absolute Pressure = Gauge Pressure + Atmospheric Pressure
A pressure of '0' indicates a perfect vacuum.
Different Applications of Bourdon Gauges
The bourdon gauge has been in existence for over 100 years in one form or another and remains today one of the most common pressure gauges available. Applications are numerous and include a variety gaseous and liquid state systems.
Repairing the gauge is rarely possible unless using specialist equipment, but Bourdon gauges are cheap and thus can be spared in their entirety.
The Bourdon gauge can be considered reliable and robust although any blockage of the piping leading to the open end of the Bourdon tube will render the gauge inoperable, or, unreliable.