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Piston vs Diaphragm

Piston vs. Diaphragm Differential Pressure Gauges

A differential pressure gauge senses the difference in pressure that is supplied to its high and low ports. This value is then displayed on a dial face via a pointer. A pressure sensing component (either a piston or diaphragm) moves against a calibrated range spring in response to differences in pressure. This linear motion inside the gauge body is transformed to rotary movement of the pointer inside the dial case by means of two coupled magnets.

Both piston and diaphragm type gauges manufactured by Mid-West® Instrument have built in over-range protection. The diaphragm or piston is protected if the input pressure on either the high or low side ports is higher than the differential pressure specified on the gauge dial face.

Piston

Mid-West® Instrument Piston ΔP Gauges– A piston type gauge senses differences in pressure by the movement of a precisely ground floating piston/magnet in a precision bore against a calibrated spring. This design allows a slight amount of process fluid to migrate around the piston from the high to low side. This gauge is often used for liquid applications or in systems where the bypass of fluid is permissible. Since liquid molecules are larger than gas molecules, the amount of fluid bypass around the piston is considered acceptable for many applications.

Diaphragm

A diaphragm type gauge senses differential pressure using a rubber diaphragm that seals and completely isolates the high and low pressure ports. There is no bypass from  the high port to the low port  and therefore, is ideally suited for use on dissimilar fluids, air, other gases, or liquids with a high concentration of solids, etc.

Chemical seals, or remote seals, can be installed on a diaphragm type gauge to isolate the instrument from the system fluid. These seals are required when the process fluid should not come in contact with the differential pressure gauge because of compatibility concerns. The Mid-West Model 140 is an ideal product to incorporate the use of chemical seals.

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