A pressure gauge is a measurement device that determines the pressure in compressed gas or liquid. There are different types of pressure gauges available to suit specific requirements.These pressure gauges are to be calibrated periodically to confirm that they are working correctly.

Liquid Column: A liquid column pressure gauge consists of a U-shaped glass tube partially filled with a liquid such as mercury. The column rises or falls until the weight is in equilibrium with the pressure differential between the two ends of the tube. Due to practical constructional limitations, this type cannot be used for high pressure applications.

Elastic: Elastic pressure gauges such as Bourdon Gauges are constructed using the principle that various elements will become elastically deformed when under pressure.

Electrical: Electrical pressure gauges use one of two methods to read pressure. A combination of strain element and elastic object. They convert the shape change caused by pressure into an electrical signal output such as voltage, current or frequency. The signal is then shown on a digital gauge.

Piston: Piston pressure gauges work on the principle of counterbalancing the pressure with a spring. In general these gauge are used for measuring tire pressure.

Working Principle of Various Pressure Gauges:
Pressure gauges can be categorized by their working principle.
PISTON TYPE
FLAT DIAPHRAGM TYPE
CORRUGATED DIAPHRAGM TYPE
CAPSULE TYPE
BELLOW TYPE
'C' SHAPED BOURDON TUBE TYPE
TWISTED BOURDON TUBE TYPE
HELICAL BOURDON TUBE TYPE

The Bourdon Tube Type Pressure Gauge, is the most adaptable kind of pressure gauge, that has been used all over the world, in many petrochemicals, and process industries. If the working fluid is corrosive, a diaphragm fitting is added to the pressure gauge as shown. This ensures that the bourdon tube or the socket in the pressure gauge does not get affected.

A liquid-filled pressure gauge is an advancement of the conventional pressure gauge. The only difference is that the dials are hermetically sealed with a viscous liquid filling. This viscous liquid filling helps in dampening the instability of the pointer, and aids in a steady reading. The two most common liquids used for filling are: - Glycerin, with a usable temperature range of 20/180°F. - Silicone Oil, with a usable temperature range of –40/250°F.

Advantages of Liquid filled pressure gauges over conventional pressure gauges:
- The internal fluid, guards the gauge components, against severe temperature instabilities and vibrations, which are the key factors, in the failure of conventional gauges.
- Liquid filled gauges, have extended lives than conventional gauges, because of their viscous fluid-filled into them.
- The liquid-filled pressure gauges, are constructed to work in rugged conditions. - They are commonly used in extremely corrosive chemical processes, such as petrochemical refining.
- In conventional gauges, condensate build-up, results in visibility issues. This can be a critical error in high-humidity working atmospheres, which can cause undesirable accidents.

The effect of temperature and mechanical alignment issues will cause zero shifts in the pressure gauge. To allow the user to adjust the pressure gauge back to the zero setting, a zero adjustment knob/ screw is provided on the pressure gauge casing. This ensures precise pressure reading.

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