Seal diaphragms, also known as chemical seals, are used to measure pressure when the process environment should not come into contact with the pressure components of the measuring device.
The flood idiopharm has two main functions:
- Separation of measurement tools from the process environment
- Pressure transfer to the measuring instrument
How does a flood diaphragm work?
Seal diaphragms, also known as chemical seals or remote seals, are used to measure pressure when the process environment should not come into contact with components under pressure.
The pressure is measured by the diaphragm of elasticity to the liquid from the medium and from there to the measuring component, the measuring instrument or transmitter.
Between the seal diaphragm and the pressure gauge is a capillary tube connected to the gauge to eliminate or minimize the effects of temperature from the hot fluid.
A closed system of flood diaphragm, capillary and measuring instrument is formed. Therefore, the flood diaphragm screw on the flood diaphragm from which the oil is filled should never be loosened.
If the flood diaphragm is leaking, system filler fluid may enter the environment.
Applications of diaphragm gauge:
- If the environment is corrosive and the pressure measuring element itself is not sufficiently protected against it.
- If the environment is very viscous and fibrous, it can cause problems with the measuring instrument due to the presence of dead spaces and restrictions.
- The environment tends to crystallize or polymerize
- If the environment has a very high temperature. As a result, the pressure gauge becomes extremely hot. Heating leads to high temperature error in pressure measurement.
Operation method and characteristics of diaphragm gauge
Diaphragm pressure gauge consists of a circular membrane made of a sheet of metal with precise dimensions, which can be smooth or wavy.
The diaphragm is mechanically attached to the moving part, which amplifies small defects in the diaphragm and transfers them to the hand.
Process pressure is applied at the lower part of the diaphragm, while the upper part is at atmospheric pressure. The pressure difference due to the diaphragm moves the diaphragm upwards and moves the hand.
Aperture deviation is negligible (1.1 mm) and the use of a high-multiplication motion is essential for rotating the hand along the entire scale of motion. Activation of such a high-ratio transmission mechanism is possible because the aperture deflection is capable of producing large forces.
Flat and wavy diaphragms
The diaphragm should be such that the deviation is linear, meaning that the same increase in pressure should always correspond to the same deviation as the diaphragm.
A flat diaphragm made of metal will only be linear when the deflection is too small, it must be too small for the hand to move enough.
At larger deflections, the flat diaphragm loses its linear position because more pressure occurs in the diaphragm. The diaphragm becomes increasingly stiff due to the increasing pressure, thus increasing the pressure drop in the diaphragm.
A flexible material, such as a thin sheet of nylon, can act as a smooth diaphragm. The diaphragm then confronts the calibrated spring, which ensures a linear position and steers the diaphragm to its starting position.
Corrugated metal diaphragms are commonly used for industrial applications. Wavy diaphragms ensure that the diaphragm is more elastic and are such that the deflection of the diaphragm is linear. There are several types of corrugated profiles that you can see in the figure below.
Application of diaphragm compression gauge
Diaphragm pressure gauges are used for relative pressure as well as for vacuum, composition and pressure difference.
Due to the diaphragm, these gauges are very suitable for use in viscous environments. For corrosive gases and liquids, the diaphragm may be coated or covered with foil.
By default, these diaphragm gauges come with a male threaded connection.
For highly viscous, impure or crystalline media, it may be necessary to use an open connection flange to prevent process connection clogging. Open connection flange is available from DN15 to DN80. The most common sizes are DN25 and DN50.
Diaphragm pressure gauge for measuring pressure difference is different from measuring relative or absolute pressure. On either side of the membrane, there is a pressure chamber that closes with a bellows. Each of these pressure chambers is connected to different pressures and creates a pressure difference in the diaphragm.
Below are the different types of apertures. Obviously, pressure difference diaphragm gauges are not suitable for highly viscous, impure, or crystallized fluids.
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