Liquid-Filled Pressure Gauges
Liquid-Filled Pressure Gauges:- Pressure gauges are mechanical devices which are used to measure the pressure exerted by the flowing fluid. There are two types of pressure gauges used industrially; Bourdon tube and Diaphragm elements:
- Bourdon tube pressure gauge: It contains a bourdon tube, a fraction of fluid gets filled inside the bourdon tube and causes the tube to move, the movement is translated to the pointer of the pressure gauge in order to get a measure of the intensity of fluid flow.
- Diaphragm element pressure gauge: It contains a diaphragm element in order to measure the intensity of the flowing fluid. Due to the design of the gauge, it is required to be flanged to the location where the pressure is to be measured. A fraction of fluid enters the gauge and causes the diaphragm to move. A mechanical link connects the diaphragm and the pointer of the pressure gauge. Diaphragm causes the link to move and then the movement of the link causes movement in the pointer which then indicates the pressure at that location.
Pressure gauges may perform poorly in the event if they are placed in a location which is subject to lots of vibrations, pulsations, pressure spikes or fogging. For example; pumps, compressors, or any other rotating components. The common performance issues which are encountered due to such scenarios are:
- Pointer flutter: The pointer fluctuates normally around a value. It causes difficulty in taking the actual readings which may introduce error in the process. This happens in case of extreme vibration and pulsation.
- Damage: Very strong pressure spikes may cause damage to the internal mechanics of the pressure gauge. Prolonged exposure to vibrations and pulsations also causes permanent damage to the gauge.
- Non-readability: If the pressure gauge is being used at locations where the temperature drops too low then condensation can form inside the pressure gauge which will cause the glass to appear foggy and hide the pointer and measurement scale.
In order to prevent the pressure gauge to perform poorly when it is subject to such conditions, a liquid is filled inside the casing. The liquid dampens the vibrations, pulsations, and pressure spikes which prevents pointer flutter. It also lubricates the internal mechanical parts which increase their durability and the liquid also prevents condensation which helps in preserving the readability. Some liquids which are used for the purposes are:
- Glycerin: Glycerin-filled pressure gauge is the most common type of fluid-filled pressure gauge used in industries. It works amazingly well near room temperature and offers good services w.r.t its value. They are used in the temperature range of -20°C to +60°C.
- Silicone: Silicone is used primarily because of its low viscosity even at lower temperatures. If there are large temperature variations which have tendency to fog or ice the inside of the casing then silicone-filled pressure gauges are used. They are used in the temperature range of -40°C to +60°C.
- Halogen: The halogen-filled pressure gauges are installed in application which has chlorine, oxygen, or hydrogen peroxide as their working fluid. They work in the temperature range of -20°C to +60°C.