Pressure

Cases are available in a wide variety of materials. The material choice is generally determined by the demands of the application. The more demanding the environment, the more rugged the case construction, for example polypropylene or stainless steel for industrial applications versus aluminium or steel for construction or commercial applications.

For a mechanical pressure gauge accuracy is defined as a percentage of the full-scale range. While requirements differ from one industry to another, the following are general guidelines:

A blow out disc is a rubber circular disc often placed on the back of the pressure gauge.

Bourdon tube pressure gauges are the most common type in many areas and are used to measure medium to high pressures. They cover measuring ranges from 600 millibar to 4,000 bar. The measuring element is a curved tube with a circular, spiral or coiled shape, commonly called a bourdon tube. This tube moves outward when the pressure inside the tube is higher than the external pressure, and inward when the internal pressure is lower. This motion is proportional to the pressure to be measured, and it is coupled to the pointer mechanism.

Analog pressure gauges are one of the most common and simple instruments used, but they are also common to errors; usually being out of tolerance or the needle not returning to zero, often due to environmental issues. However, some analog pressure gauges are easily adjusted. A calibration screw is often used as part of the design to correct ‘faulty’ analog pressure gauges, although not all analog pressure gauges have a calibration screw

A pressure gauge syphon is a device used to protect pressure gauges against the effect of high-temperature environments as well as reducing the effect of pressure surges that could potentially damage the function of a pressure gauge.

A snubber (also called a check valve) protects a pressure gauge against pressure spikes and sharp fluctuations. It helps to prolong the life of a gauge when used in challenging or harsh conditions. Without a snubber, a rapid change in pressure can cause internal seals within the gauge to rupture, thus allowing the liquid media under pressure to enter the gauge.

When selecting a suitable dial for a given application there are three main areas of consideration. These are:

The normal operating pressure should be confined to between 25% and 75% of the scale, if process pulsation is present then the maximum operating gauge pressure should not exceed 50% of the full-scale range. The scale on Brannan’s standard industrial range is usually printed in either bar, psi or dual scale (bar & psi).