# Understanding Bourdon Pressure Gauge

Just like other types of pressure gauges, the Bourdon pressure gauge is used to measure pressure. The Bourdon-tube gauge, which was invented in 1850, is still one of the most extensively used instruments for measuring the pressure of various types of liquids and gases, including steam, water, and air up to 100,000 pounds per square inch (70,000 newtons per square cm). It is made up of a circular tube that has been flattened and coiled into a circular arc.

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## What is a Bourdon pressure gauge?

Bourdon tubes have an oval cross-section and are radially formed. The measuring medium’s pressure acts on the inside of the tube, causing movement in the tube’s non-clamped end. The pressure is measured by this motion, which is indicated by the movement.

For pressures, up to 60 bar, C-shaped Bourdon tubes with an angle of around 250° can be employed. Bourdon tubes with numerous superimposed windings of the same angular diameter (helical tubes) or spiral tubes with a spiral coil in one plane (spiral tubes) are utilized for higher pressures.

Pressure gauges made of Bourdon tubes are used to measure relative pressures ranging from 0.8 to 100,000 psi. They are mechanical pressure measurement tools that do not require any electricity to work. The followings are the applications of a Bourdon pressure gauge:

• They are used to measure pressures ranging from medium to very high.
• For high-pressure applications, such as steam boilers and compressors.
• Used for measuring pressure in vehicles’ tube tires.

#### Diagram of a Bourdon pressure gauge:

Read more: Understand the various types of relays

## Construction

An elastic transducer, which is a bourdon tube that is fixed and open at one end to accept the pressure to be measured, is the major component of this instrument. The bourdon tube’s other end is open and closed. The bourdon tube has an oval cross-section. The bourdon tube has been bent into the shape of a circular arc. An adjustable link is joined to the free end of the Bourdon tube, which is connected to a sector and pinion. A pointer is attached to the pinion’s shaft and sweeps across a pressure-calibrated scale.

## Working Principle

The working of a Bourdon pressure gauge is less complex and can be easily understood. The pressure to be measured is connected to the bourdon tube’s fixed open end. The exerted pressure acts on the bourdon tube’s inner walls. The cross-section of the bourdon tube tends to transform from elliptical to circular as a result of the applied pressure. This tends to straighten the bourdon tube, causing the free end of the bourdon tube to be displaced.

The applied pressure is proportional to the displacement of the free-closed end of the bourdon tube. The displacement is amplified and translated to a rotating motion of the pinion when the free end of the bourdon tube is attached to a link–section – pinion configuration.

As the pinion spins, the pointer moves to a new position on a pressure-calibrated scale, allowing the applied pressure to be directly indicated. The pointer represents gauge pressure because the pressure in the casing containing the bourdon tube is normally ambient.

#### Watch the video below to learn more on the working of a Bourdon pressure gauge:

The followings are the advantages of a Bourdon pressure gauge in its various applications.

• The Bourdon tube pressure gauges provide precise readings.
• The Bourdon tube is inexpensive.
• The manufacture of Bourdon tubes is simple.
• They can be made to provide electrical outputs by modifying them.
• Even for high-pressure measurements, they are safe.
• The accuracy is excellent, particularly at high pressures.

Despite the good advantages of a Bourdon pressure gauge, some limitations still occur. Below are the disadvantages of a Bourdon pressure gauge in its various applications.

• They react slowly to pressure changes.
• Hysteresis is applied to them.
• They are susceptible to vibrations and shocks.
• Because the displacement of the free end of the bourdon tube is so little, amplification is required.