What is a pressure gauge?
A pressure gauge is a device that measures pressure in a compressed gas or liquid.
Pressure gauges are used across many industries. Everyday examples of use include
measuring tyre pressure or blood pressure. In industry, gauges monitor pressurised systems
whether it’s a refrigeration system in food processing or equipment in a nuclear power plant.
Standard pressure gauges take a reading of pressure against ambient atmospheric pressure.
These would be used in boilers and all kinds of compressed air systems. Vacuum gauges and
absolute gauges take readings against an absolute vacuum. Equipment for atmospheric, deep
vacuum or altimeter readings would need to measure absolute pressure.
Other types of gauge include digital display pressure gauges which can make readings easier or
gauges with analogue dials which are linked directly to the gauge.
What is calibration?
Calibration is the process of testing and then correcting the accuracy of measuring equipment.
Measuring equipment will lose accuracy over time and calibration is vital to ensure the reliability
of recordings. For any industry relying on the precision of measurements, for example pressure
and temperature readings, a trusted calibration service is essential.
What are the standard process connections used to connect a pressure gauge to my application?
We have an information page dedicated to gauge process connections, click here to visit.
The most common process connection used in the UK is BSP (British Standard Pipe) which has a parallel thread and a spigot on the bottom. The pressure tight seal is made using a bonded washer.
The other commonly used process connection is NPT (National Pipe Thread) which is used most in other countries, particularly the USA. A pressure tight seal is made upon a tapered thread (generally a PTFE tape).
Process connections are most commonly available in 1/8″, 1/4″, 3/8″ and 1/2″ in both BSP and NPT sizes*:
* BSP and NPT process connection sizes do not relate to the physical size of the connection or thread.
We have a process connection information page which provides full details on the most commonly used threads including their physical dimensions.
Absolute, Gauge and Differential Pressure – What do they mean?
Absolute, Gauge and Differential are completely different methods of recording pressure.
Gauge pressure is the deviation of a particular pressure away from atmospheric pressure. It can be positive or negative.
For example, a dial pressure gauge whose pointer reads zero when no pressure is applied would usually measure gauge pressure. Gauge Pressure is by far the most common measurement process used worldwide.
Absolute pressure is a measurement of pressure relative to a complete or absolute vacuum. It will always be positive.
For example, a barometer measures absolute pressure.
Differential pressure is the measurement of any pressure relative to another pressure. It can be positive or negative.
For example, a manometer used to measure the pressure drop across an air filter is measuring differential pressure.
What is the Accuracy class?
The Accuracy class is a way of measuring acceptable levels of error in pressure equipment. It is given as a percentage of the scale reading span. For example, an accuracy class 4 on a 10 bar pressure gauge would indicate that readings may deviate by +4% or +0.4 bar across the measuring range.
Why are there yellow levers on the pressure gauge casing?
For pressure ranges under 363 psi (25 bar), gauges tend to have something called a filling plug. These plugs come with small yellow levers which are closed when delivered. You must ensure you open these when fitting so that pressure does not build up in the case. This pressure causes unacceptable high accuracy deviations for the gauge.
What is the difference between a standard pressure gauge and a safety pattern gauge?
Safety pattern gauges are generally used in the gas industry and are designed with operator safety in mind. They are constructed with an additional solid baffle wall welded between the dial and the measuring system. The case also has a safety glass window and a back wall that can blow out completely in the case of a rupture.
When should a restrictor be used?
Restrictors are used to regulate the flow of sudden changes in pressure, sometimes known as “spikes”. The restrictor is fitted into the pressure gauge socket and forces the fluid through a small space restricting the flow of fluid to the element. By protecting the sensor from sudden pressure fluctuations, you will enhance the performance and longevity of your pressure gauge.
What is ATEX?
ATEX is a combination of two EU directives detailing what equipment is to be used in a workplace with a potentially explosive environment: The 94/9/EC Equipment Directive and the 99/92/EC Workplace Directive.
ATEX is a synonym taken from the French title of the 94/9/EC directive “Appareils destinés à être utilisés en Atmosphères Explosibles”.