In the process industries, there is often a requirement for measuring the pressure exerted by any fluid or gas. Diaphragm is usually used extensively to measure this kind of pressure, which has got a certain elastic property.
A diaphragm pressure gauge measures the fluid pressure in a system by measuring the deflection of a thin, flexible membrane. As a result of the diaphragm’s ability to separate internal parts from the media, this gauge can be used with corrosive or tainted liquids or gases.
This gauge is utilized for low-pressure measurements, such as checking the pressure in gas canisters or measuring the atmospheric pressure. Additionally known as flexible membrane pressure gauges.
Working principle of diaphragm pressure gauge
A diaphragm pressure gauge gets deformed when a certain pressure is applied by a fluid or gas. That is because its material has got an elastic property. This deformation is then converted into a readable measurement using mechanical linkages and an indicator needle.
The diaphragm pressure gauge is made out of a few key components:
- A flexible diaphragm
- A chamber for the process fluid
- Reference chamber
- A mechanical linkage system
- A calibrated scale.
Let us now try to understand the role of each of these components in the following paragraph:
- Diaphragm
This is the main part, which as mentioned before is made of any of the following:
- A metal
- A composite material.
Whenever any pressure is ever applied to this diaphragm it can easily get deformed because it is usually a very thin and circular membrane.
Due to its elastic property, it can be effectively used for converting into a certain mechanical movement by applying a certain pressure on the diaphragm.
- Process fluid chamber
As you would like to measure the pressure of a process fluid, hence this fluid will be connected on one side of the above diaphragm. As the pressure is applied to the surface of the diaphragm it will move either inward or outward.
As a result, the diaphragm will separate the process liquid from various components inside the gauge.
- Reference chamber
If you notice carefully then you will see that in the diaphragm’s opposite side, one reference chamber is located, which is usually filled either with air or some other gas. This reference chamber provides a counteracting force against the pressure applied by the process fluid.
The pressure in the reference chamber is either kept constant or allowed to change under controlled conditions.
- Mechanical linkage system
Whenever any difference of pressure will be created between the above reference chamber and another mechanical linkage system, it is going to convert this movement of the diaphragm in the form of a mechanical output.
This linkage system may consist of the following:
- Levers
- Gears
- Pivots
All these can amplify any little movement of the above diaphragm to much more movement, which can easily be seen and also measured.
- Indicator needle and calibrated scale
The mechanical movement produced by the linkage system is then transferred to an indicator needle that moves across a calibrated scale. This scale is marked with pressure units and corresponding values.
As the diaphragm deflects, the indicator needle moves along the scale to indicate the pressure value of the process fluid. The scale is calibrated during the manufacturing process to ensure accuracy.
Let us now try to summarize the diaphragm’s working principle in the following few steps:
- Application of pressure
There are two different pressures applied:
- From one side of the diaphragm, there is the pressure exerted by the process fluid
- From the other side, a reference chamber’s pressure will be connected.
- Diaphragm deformation
The diaphragm will either flex inside or outside because of the difference in pressure between the process fluid as mentioned above and the reference chamber. The extent of this deformation is proportional to the applied pressure.
- Linkage system
The diaphragm’s movement is transmitted through the mechanical linkage system, which amplifies the small diaphragm movement into a more noticeable mechanical displacement.
- Indicator needle movement
The mechanical displacement of the linkage system is translated to the movement of the indicator needle on the calibrated scale.
- Pressure reading
The position of the indicator needle on the scale corresponds to the pressure value of the process fluid. By reading the value indicated by the needle, the pressure of the process fluid can be determined.
Diaphragm pressure gauges find application in various industries where accurate pressure measurement is essential. They are preferred for systems with low to moderate pressures due to their reliability, simplicity, and ability to handle corrosive or viscous fluids.
A flat and corrugated diaphragm – Which is the better option?
The diaphragm must deflect linearly such that each time there is an increase in pressure, there is a corresponding decrease in deflection. Only if the deflection is smaller will a flat metal diaphragm be linear.
The flat diaphragm loses linearity with a bigger deflection because it experiences increasing amounts of stress and stiffens as a result.
A corrugated metal profile diaphragm is typically utilized for industrial applications. In comparison to a flat diaphragm, a corrugated diaphragm guarantees linear deflection and is more elastic.
The following are a few advantages and disadvantages of diaphragm pressure gauges:
Advantages:
- They are quite sensitive
- It can measure fractional pressure differences easily at the minute range
- It only requires less space
- This kind of pressure measurement device can be used for measuring low-pressure, vacuum, or any differential pressure
- It is used in corrosive environment.
Disadvantages:
- These are quite challenging to fix
- These may not be appropriate for measuring very high pressure.
- They require defines against vibration and stress.
How can you install a diaphragm gauge?
If the temperature and pressure are suitable at the tapping location, these instruments must be close by. Pressure gauges with parallel threads must be properly sealed, which can be accomplished using the right seal rings.
The pressure media that is damaging to the diaphragm element can be separated using diaphragm seals. The diaphragm seal and pressure gauge connection must be correct.
