# Pressure Indicator

Written by Jerry Ratzlaff on . Posted in Pressure Instrument

## Pressure Indicator

A pressure indicator ( $$PI$$ ) is also known as a pressure gauge.  It is a field instrument that requires little to no maintenance.

## How it Works

Process Pressure Gauges function when the process fluid enters a Bourdon Tube or similar enclosure.  The Bourdon pressure gauge uses the principle that a flattened tube tends to straighten or regain its circular form in cross-section when pressurized. The amount of deflection in the tube drives a needle to display the pressure in the line.  Depending on the pressure range, the Bourdon Tube will connect to a gear box to accurately measure the pressure.

## Specifying

When choosing a PI, it is most important to select the correct materials that are in contact with the process. In steam applications special options may need to be selected.

Sometimes, when the pressure indicator is installed downstream of a pump or in a service where there is high vibration, it may be necessary to have the case filled with fluid such as glycol or other oil.  Glycol helps dampen the movement of the needle.

Common pressure ranges are listed below.  When selecting a pressure gauge, it is good practice to select a gauge where the operating pressure is halfway between the indicated range.  For example, when operating pressures are 60 psi, a 0-100 psi range is appropriate.

PSI
0-15
0-30
0-60
0-100
0-160
0-200
0-300
0-400
0-600
0-800
0-1000
0-1500
0-2000
0-3000
0-5000
0-10,000
0-20,000
0-30,000
0-50,000
0-80,000
0-100,000