To measure absolute pressure, gauge pressure, vacuum or draft pressure and differential pressure three physical methods can be used based on the working condition
Using a liquid column where density and height of liquid are important to measure pressure.
Using a pressure sensing elements
By electronic methods
Let’s see pressure gauges of different types and pressure range they can work.
Diaphragm Pressure Gauge:
This pressure gauge is widely used to measure the pressure of a reactor or closed container.
When pressure is applied on either side of the tight diaphragm, by which it gets deflected. This deflection of the diaphragm is proportional to the differential pressure across it. Thus differential pressure across the diaphragm can be measured in terms of its deflection.
Construction and working:
Diaphragm gauge uses metallic or non-metallic diaphragms along with the pointer mechanism.
- Metallic diaphragms: These elements are flexible circular discs, either flat or corrugated. These elements convert pressure signal to pointer deflection.
The metal is heat treated before forming a diaphragm to produce a maximum elastic limit. After forming, the diaphragms are heat treated to relieve internal stresses. A diaphragm is usually designed so that the deflections versus pressure characteristics are as linear as possible over a specified pressure range. Metals used are brass, beryllium-copper, stainless steel and phosphor-bronze.
- Non-metallic diaphragms: very bendable diaphragms are used and so they can be utilized to measure vacuum and low pressures available. Non-metallic materials used are synthetic rubber, neoprene, leather, Teflon, nylon or dacron.
For non-metallic diaphragm 0 to a 10-inch water
Minimum= 0 to 2 inch of water
Maximum=0 to 400 psi
- Small in size and cheaper
- By using corrosion resistant material it has a long life
- We can obtain perfect linearity functions
- Cannot be used for high pressure
- Vibration will affect the reading