Display types include graphical and video displays, digital readouts or analog meters and needles.
Gas pressure gauges indicate the internal pressure of whole systems or individual vessels and are essential for applications where the accurate function of a system or vessel depends directly on the correct pressure as determined through gauges. Gas pressure gauges are constructed of stainless steel, bronze, brass and aluminum. The internal components are held inside a metal housing and the viewing window is made from double-strength glass. Some gauges require rubber or plastic seals, plugs or rods.
Pressure gauges are a type of sensor and are usually combined with other instruments or devices such as shutoff valves, couplings or fittings. Pressure gauges can also be equipped with electric contacts to turn on signal lights, sound alarms or operate a pump or valve. Gas pressure gauges vary in style, size and material, depending on the application; they are widely used, especially by manufacturing plants or industrial companies where it is important to monitor any changes in pressure in order to control the rate of flow of gases such as propane or natural gas.
There are two main kinds of gauges: hydrostatic and aneroid. Hydrostatic pressure gauges use liquid to compare pressure to the pressure exerted by the force of gravity on a fluid at equilibrium. These measurements are independent of the type of gas that is being measured, and they have poor dynamic response, so they are not generally used for gas. The majority of gas pressure gauges are aneroid. Aneroid pressure gauges use a flexible metal membrane that bends, curls or twists according to the pressure being exerted.
Aneroid gauges are able to evaluate both liquid and gas pressure and do not need to use any liquid to do so. Within this category are Bourdon tubes and diaphragm gauges, both of which use bellows. A C-shaped or coiled tube in the Bourdon gauge is connected to the system or vessel where the pressure must be read. The tubes coil and uncoil depending on a decrease or increase in pressure.
A diaphragm gauge uses a membrane sealed in between two regions of varying pressure. The membrane flexes or deflects and the deformation is measured as the pressure. Even the slightest bend in the bellows or membrane is detected by the pressure sensing element and transmitted to the display.