Bellows Pressure Gauge Working Principle

Bellows are made of springy metal formed in the shape of thin wall tubes. The tube is then shaped to form deep convolutions,which enable the element to expand in much the same manner as anaccordion. The bellows are sealed on the free end; pressure is applied toan opening on the stationary end. Pressure applied to the inside acts on the inner surface, producing a force that causes the bellows to expandin length, thus producing movement at the free end. Because of the relatively large surface area compared to physical size, the movement-to-pressure ratio is greater than for the devices previously discussed. Bellows are more sensitive, very accurate, and used primarily for lower-pressure applications found in receiver instruments. 




Applications of  Bellows Pressure  Gauge :-

Bellows-type sensing elements are for low to intermediate pressures and vacuumswith atmospheric (compound) or vacuum (absolute) reference. They are also used in differential pressure applications.

Design Pressure Bellows Pressure  Gauge :

Up to 25 PSIG (172 kPa) with evacuated motion balance type bellows; up to 375 PSIG (2.6 MPa) with evacuated force balance bellows; up to 100 PSIG (690 kPa)with motion balance bellows, which are provided with atmospheric reference; up to 6000 PSIG (41 MPa) with dual bellows element; up to 4000 PSIG (27 MPa)with atmospheric reference force balance bellows.

Materials of Construction Bellows Pressure  Gauge :

Brass, stainless steel, beryllium copper, Monel, bronze, copper, Inconel, Ni-Span

Range of Bellows Pressure  Gauge :

Absolute pressure ranges from 0 to 0.326 PSIA (0 to 2.5 kPa); also, 0–100 mm Hg to 0–35 PSIA (0–13 to 0–240 kPa); gauge pressure ranges from 0–2.5 in. H 2 O to0–2000 PSIG (0–0.65 kPa to 0–14 MPa); gauge vacuum ranges are available from − 0.326 to 0 PSIG ( − 2.5 to 0 kPa); compound ranges are available from − 0.196 to0.13 PSIG ( − 1.5 to 1.0 kPa).

Price of Bellows pressure Gauge:

$150 to $500 for indicators and switches; $400 to $1200 for direct recorders; $800to $2000 for direct controllers and transmitters.



Bellows pressure gauge advantage and disadvantage

Advantage:

Disadvantage :

  • It is not useful to measure high value pressure
  • Bellows joints can fail catastrophically.
  • No in place maintenance or repair can be performed – they must be replaced if damaged.