Diaphragm pressure gauge working principle

Diaphragms pressure gauge used for very low pressure measurement ranges are usually made of soft, pliable material, either metallic or fibrous. This type of pressure element is sensitive to very little pressure and can be used to measure full-range pressure values as low as 5 to 10 inches of water. The increased sensitivity of diaphragm pressure elements is attributable to the large surface area of the element. It should be remembered from previous discussions that force is equal to pressure times area (F = PA).The force exerted by a pressure

element is therefore directly proportional to the area of the device over which the pressure is exerted. For this reason, high pressure can be measured by pressure elements with relatively small surface areas. Such pressure elements are characterized by the small amount of are a exposed to the process pressure. Diaphragms, on other hand, regard-less of physical configuration, can be characterized by the relatively large surface area exposed to the pressure to be measured. The most extensive use of diaphragm pressure elements is in pressure gages and pressure transmitters. The pressure elements discussed in this section convert the applied pressure acting over the surface area of the element to create a force or movement and are the primary transducers in pressure measuring devices. A secondary transducer converts the force or motion of the primary transducer to an indication when used in pressure indicators and a scaled signal for transmission in the case of transmitters.

Advantages and disadvantages of bellows pressure gauge

Diaphragm pressure gauges Advantages:
  •  Excellent load performance
  • Linearity
  • Suitable for measuring absolute pressure, differential pressure
  • Small size, affordable
  • Can be used for viscous, slurry measurement.
Diaphragm pressure gauge Disadvantages:
  • Seismic, impact resistance is not good
  •  Difficulty in maintenance
  •  Lower measurement pressure.

Applications of the diaphragm pressure gauge

Pressure gauges with horizontal diaphragm allow to find suitable versions for even difficult kinds of media, such as aggressive, contaminated or viscous media. The stainless steel bayonet ring case is designed for applications, where a rust-resistant, sealed case of high chemical resistance is required (dirty damp, or corrosive atmosphere).
  • For measuring points with increased overload
  • With liquid-filled case suitability for high dynamic pressure loads and vibrations (model 433.50)
  • For gaseous, liquid and aggressive media, also in aggressive environments
  • With the open connecting flange option also for contaminated and viscous media
  • Process industry:
    • Chemical, petrochemical, power plants, mining,
    • on-/offshore, environmental technology,
    • machine building and general plant construction

Difference between bourdon tube and diaphragm pressure gauge

The working principle of the pressure gauge is through the elastic deformation of the sensitive element in the gauge. Then the pressure change is transmitted to the pointer by the conversion mechanism of the movement in the watch. Cause the pointer to rotate to show pressure. Sensitive element may be a Bourdon tube, diaphragm, bellows.

Therefore, the essential difference between the bourdon tube and diaphragm pressure gauge is the different sensitive components for pressure measurement.

Diaphragm pressure gauge:

The sensitive element of the Diaphragm is composed of two membranes with circular waves connected together. The pressure of the measuring medium acts on the inside of the capsule cavity. The resulting deformation can be used to indirectly measure the pressure of the medium. The pressure value is indicated by the pointer. The capsule pressure gauge is generally used to measure the pressure of the gas, and it can also measure the micro-pressure and over-pressure protection to a certain extent. When several bellows sensitive components are stacked together, a large transmission force will be generated to measure very small pressure.

Bourdon tube pressure gauge:

The sensitive element of the Bourdon tube is an elastic C-shaped tube bent into a circle with an oval cross-sectional area. The pressure of the measuring medium acts on the inside of the wave tube. In this way, the elliptical cross-section of the Bourdon tube will tend to be circular. Due to the slight deformation of the Bourdon tube, a certain ring stress is formed. This ring stress causes the Bourdon tube to extend outward. Since the head of the elastic Bourdon tube is not fixed, it will deform slightly. The amount of deformation depends on the pressure of the measuring medium. The deformation of the Bourdon tube displays the pressure of the measured medium indirectly by the pointer through the movement.