Pressure Gauges are mechanical pressure measuring instruments that can be used to measure gauge, absolute or differential pressure. The method of measurment can be via Bourdon tube, diaphragm element or capsule element. Pressure Gauges, especially Bourdon pressure gauges are inexpensive and if selected and installed correctly can give years of trouble free use. This is what makes them the most widely used instrument on a typical oil and gas platform.
Pressure Gauge Selection
Typical points spcified for pressure gauges used in the oil and gas industry include:
- Pressure gauges shall have safety glass or plastic lenses. Lenses are to be compatible with the surrounding environment (temperature limitations or resistance to attack from fluids or vapours)
- Pressure gauges shall have blowout protection, and weatherproof, corrosion resistant cases. Comment: Blowout protection prevents release of any process material out the case front or face
- Pigtails or siphons shall be used in steam and other high temperature condensable vapour services.
Standard Ranges for Pressure Gauges
When deciding on the range of pressure gauge for a particular application, try to choose from the "standard" ranges that most suppliers offer. Typically these ranges, in bar, are:
Pressure Gauge Installation
- Before fitting the gauge to a pressure source check that the maximum scale value of the gauge is higher than the pressure applied. The applied pressure should be 75% of the max scale value for steady pressures or 65% of max scale value for fluctuating pressures
- Before fitting the gauge to a pressure source check that the wetted parts are compatible with the fluid being used, and that the pressure connection correctly matches that of the pipework. When fitting the gauge to the pipework, use a correct sealing methods
- Do not use the gauge case to tighten the gauge to the pipework, use a correct size spanner on the neck of hexagon
- Pressure Gauges with blow-out release at the back must be mounted at least 20 mm away from a panel or wall to ensure safe dissipation of the confined pressure should the tube fracture
- Gauges marked "Hydraulic" must not be used on compressed gases
- Gauges must have "Oxygen" or "Acetylene" marked on the dial if used on these gases
Use of Pressure Gauges
- Do not use glycerine filled gauges for any fluid which has strong oxidising agents, e.g. chlorine, hydrogen, peroxide etc.
- The ambient and process temperature acting on the gauge should be within -70oF to + 180oF and protected from higher fluid temperature by means of a syphon tube filled with condensate before use
- The fluid in the pressure chamber should not be allowed to freeze or crystallise as this will lead to rupture of the sensing element
- Should the pointer of any pressure gauge not return to zero, when the pressure is removed, it is an indication that damage to the gauge has occurred and the gauge should be replaced immediately.