Types of pressure gauge based on the working principle

[sivaranjith]

Pressure gauges are devices used to measure pressure, all pressure gauges have their own sensing element, which senses the value of the measured quantity.

There are different types of pressure gauge available, common types available are:

• Diaphragm

• Bellow

• Bourdon tube

Diaphragm pressure sensing element:

The diaphragm is an elastic membrane that elongates when pressure is applied to it. The diaphragm is a single sheet which elongate, Joining two diaphragm to form a capsule.

Two capsules joining to form a stacked diaphragm.

Adding more capsules to the diaphragm increases the sensitivity of the gauge.

When pressure is applied to the diaphragm, it flexes. The movement is transmitted by a link that connects to the pointer. The pointer moves to indicate the amount of pressure applied to the diaphragm. The diaphragm stays at the original position until a pressure is applied to it.

Bellow sensing element:

The below is another type of stacked diaphragm. The stacked diaphragm is made of several sheets, while the bellow is made of single sheet.

The applied pressure makes the bellows expand. The expansion causes the bellows to get longer. When pressure is removed, the bellows get shorter.

The movement of the bellows will be transmitted by a link connected to a pointer. The pointer indicates the pressure applied to the bellows.

The Bourdon tube:

The bourdon tube is the ‘C’ shaped tube shown in the above figure. When a pressure is applied to the tube, the tube stretches outwards. The tube end is attached to a pointer using a link. The link-gear system makes the pointer moves along the scale. The circular motion of the pinion gear drives the position of the pointer to indicate the amount of pressure applied to the Bourdon tube.

Check out how Pressure transmitter Calibration is done and about pressure relief valves

[Gino]

There are different measuring principles for pressure gauges, but it all comes down to using another type of sensing element. Which type will be used depends on your application. 4 types of pressure sensing elements are used.

Bellows

Bellows are thin-walled metallic cylinders, with deep convolutions, of which one end is sealed and the other end remains open. The closed end can move freely while the open end is fixed.

Diaphragm

The diaphragm pressure gauge consists of a circular membrane, made from sheet metal of precise dimensions, which can either be flat or corrugated. The diaphragm is mechanically connected to the transmission mechanism which will amplify the small deflections of the diaphragm and transfer them to the pointer.

Capsule

The sensing element of a capsule pressure gauge consists of two corrugated diaphragms welded together at their periphery to form a capsule. The pressure to be measured is introduced into the capsule via an opening in the center of the first diaphragm. The center of the second diaphragm is connected to the transmission mechanism so that the deflection of the measuring element can be transmitted to the pointer.

Bourdon

The Bourdon tube pressure gauge consists of a circular tube which is bent over an angle of generally 270°, and of which one end is closed and the other is connected to the process pressure. With the pressure applied to the inside, the tube tends to straighten out. The movement of the tip will be amplified by the transmission mechanism. Besides the C-type sensing element, there are also the spiral type and helical type