Bellows Pressure Gauge | Bellows type PG

Bellows pressure gauge:- Bellows type Pressure Sensing elements are for low to intermediate pressure. They are used in vacuum, absolute and differential pressure applications. The bellows expands or contracts based on the pressure difference across the inside and outside of the bellows unit.

The bellows are sealed on the free end; Pressure is applied in the open port of the fixed end. Pressure applied to the inside acts on the inside surface, producing a force that causes the bellows to expanding length, thus producing motion on the free end. Because of the comparatively large surface area in comparison with physical dimension, the movement-to-pressure ratio is bigger than for the devices beforehand mentioned. Bellows are extra sensitive, very accurate, and used primarily for lower-pressure functions present in receiver devices.

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BELLOWS PRESSURE GAUGE

Basic designs of bellows pressure sensor will be described. They are classified by the reference pressure used as absolute, gauge or differential pressure detectors.

Absolute gauge (Using bellows)

When absolute pressure is to be sensed with bellows elements it normally involves two bellows. Out of two bellows one for measuring and the other for reference bellow element. The reference bellow element is fully evacuated and sealed while the sensing element is connected to the process. The pressure of the media to be measured is compared against a reference pressure which is equal to absolute zero in this arrangement an increase in process pressure will cause the measuring bellows to extend which results in an increase of read out through the motion balance mechanism.  If the process pressure is constant but the barometric pressure changes, force will be exerted equally on the outside of both bellows causing no change in the read out. The evacuated bellows are capable of compensating for barometric pressure variation as high as 100 mm of mercury.

absolute pressure gauge

When bellows are used as the pressure sensing element, it is desirable to add a spring for ranging and accurate characterization.

Without the calibration spring, Temperature effects and work hardening of the bellows would cause a loss of accuracy.

BELLOWS PG

 

Differential Pressure Gauge (Dual Bellows)

Dual bellows elements are also available as differential pressure sensors. Two sealed pressure media Chambers are separated by the measuring elements. If both operating pressures are the same, no movement occurs and no pressure indicated. When one of the pressures is either higher or lower than the other, reading will be indicated. If either the low or the high pressure side is left open to the atmosphere, the unit will detect either gauge pressure or vacuum.

bellows differential pressure gauge

Advantage

  1. High over load capacity.
  2. Pressure ranges can be between 0 to 60 Mbar

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