Pressure Measurement

What is a diaphragm pressure gauge?

A diaphragm is a material that would be elastic and if we apply pressure to this then it would displace. This type of pressure gauge would use the elastic property of the diaphragm to determine the difference between reference pressure and unknown pressure. The operating principle of this device is the same as the bourdon gauge. The major difference from a bourdon gauge is that this device has a corrugated diaphragm instead of a bourdon tube. So if we fit this device to any gauge point, then the diaphragm will undergo elastic deformation. This type of pressure gauge is mostly used because it only needs less space. The diaphragm pressure gauge is mostly used for low-pressure applications. This device would have a thin disk of material and it would blow outwards.

What is the need for diaphragm pressure gauge?

The diaphragm is designed in a way that the deflection versus pressure characteristics would be as linear as possible over a specified pressure range and with less hysteresis and also less shift in the zero points. The diaphragm pressure gauges are used to measure the gases and liquids and it is used to do the low-level pressure measurement.

How to select a pressure gauge?

  • It must be selected according to the required accuracy
  •  Operating pressure range
  • Operating temperature range
  • We must also consider the vibration, pulsation, and shock
  • Pressure fluid composition
  • Mounting requirements
  • Dial size must be considered
  • We must also consider the chemical compatibility with gauge construction

How does a diaphragm pressure gauge work?

The diaphragm is the name given to a flexible disc that would transmit pressure. This device’s major part consists of one circular diaphragm clamped between two flanges. The diaphragms that are used in pressure gauges are hollow, flat discs with a corrugated surface. If the pressure is applied to this device then it will bulge and this movement is transferred to a pointer using levers, gears, and pivots. The bulge or deformation will be proportional to the applied pressure. The corrugated disc can be built into stacks to produce very sensitive gauges. The material that is used for the manufacturing of this device is almost the same as the bourdon tubes. Because of the corrugation, large deflections could be permitted, for the given thickness, that what can’t be obtained by a normal-disc. If their number and depth are good then it would give good sensitivity.

What are the types of diaphragm pressure gauges?

There are two types of diaphragm pressure gauges and they are metallic and non-metallic.

Metallic type

The metallic type has one or more capsules and each of them would have two diaphragms which would be bonded together by soldering or welding. The most used metals for this device would be brass, stainless steel, and beryllium copper.

Non metallic type

This type of diaphragm is used for containing the pressure and it would exert a force on the opposing elastic element. The diaphragm would be flexible it would be made up of rubber, leather, or plastic. The diaphragm movement is opposed by a spring which would determine the deflection for the given pressure.

How to install a diaphragm gauge?

This type of instruments must be located near the tapping place if the temperature and pressure at this place are ok. We must do the correct sealing of the pressure gauges with parallel threads and it can be done with proper seal rings. Diaphragm seals can be used to separate the pressure media which is harmful to the diaphragm element. The connection between the diaphragm seal and the pressure gauge must be proper.

What are the advantages of the diaphragm pressure gauges?

  • They are really sensitive
  • It can measure fractional pressure differences at the minute range
  • It only needs less space
  • This type of pressure measurement device is used for the measurement of low pressure, vacuum, or differential pressure.
  • It can be used in corrosive environments

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