Millibar pressure gauge
If a pipe with an oval cross section is pressed, its cross section tends to change from an oval to a circle.
Making a Bordon gauge device
Bourdon gauge tubes consist of a circular tube. One end of the tube is fixed while the other end is free to undergo elastic deformation under pressure. The fixed end is open and a measurable pressure is applied to the fixed end. The free end is closed and deforms under pressure. Due to the applied pressure, the circular tube tends to bounce.
Basics of pressure suffering
Three pressure scales are used to measure pressure.
Absolute pressure suffering
Gage pressure suffering
Vacuum pressure range
In the pressure gauges shown in the figure, all barometers show a reading of 20, but their pressure values are different.
Gauge A: Shows an absolute pressure of 20 pounds per square inch.
Gauge B: Shows a pressure of 20 pounds per square inch.
Gauge C: Shows a pressure of 20 inches of vacuum mercury.
To understand why these barometers show different amounts of pressure, you need to understand the concepts of absolute pressure, gauge pressure, and vacuum pressure.
Absolute pressure suffering
Absolute pressure is when the pressure is measured using no pressure as the starting point. Air, which is a combination of gases, weighs. It absorbs gravity. At sea level, the “standard” weight of the Earth’s atmosphere puts a pressure of 14.7 PSI on the atmosphere.
Since we are all always under the pressure of the Earth’s atmosphere, we may not think about it at all and consider the Earth’s atmosphere to be zero. However this is a very real pressure. If we take all the air out of a closed chamber, no pressure will enter the chamber, so the pressure will be completely zero.
The absolute pressure scale uses the absolute zero pressure as the starting point. Absolute pressure is the complete absence of pressure, even atmospheric pressure. The pressure reading of the Absolute Pressure Scale is expressed in pounds per absolute square inch (PSIA).
A disconnected sphygmomanometer that uses the Absolute Pressure Scale reads an accurate 14.7 PSIA.
Absolute pressure = atmospheric pressure + gauge pressure
Pressure gauge
Pressure gauge is the measurement of pressure using atmospheric pressure as the starting point and summoning of this pressure. Most pressures measured in gas / oil processing are gauge pressures. The gauge pressure uses atmospheric pressure as the starting point for all measurements. This means that the gauge starts from zero even if there is atmospheric pressure on it.
A pressure gauge without a pressure connection that reads is zero.
Gage pressure = absolute pressure – atmospheric pressure
Vacuum pressure range
Vacuum is a space that has no air. In hydrocarbon processing plants, vacuum means less pressure than atmospheric pressure. Vacuum pressure is usually measured in inches of mercury. Zero reading in a mercury vacuum device is equal to atmospheric pressure. The vacuum scale is used to measure pressure in pipes or vessels under atmospheric pressure.
Reads a non-connection barometer with zero vacuum scale.
Advantages of pressure gauge
- to be cheap
- Good accuracy even for low sufferings
- High-suffering gauges also work great
- This device can be easily used with electrical devices such as LVDT.
Disadvantages of pressure gauges
- Susceptible to shock and vibration
- Gauges are prone to hysteresis
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