Pressure Measurement · Glossary

What is a Diaphragm Seal?

remote or direct sealPressure Measurement

A diaphragm seal isolates a pressure instrument from the process with a flexible diaphragm and a sealed fill fluid.

Diaphragm Seal Explained

The process pushes on the diaphragm, and the fill fluid carries the pressure to the sensor, either directly or through a capillary. Seals are used for hot, corrosive, viscous, crystallising or sanitary service.

Seals add temperature error and slow the response, especially with long capillaries. Keep capillaries short, equal on both sides of a DP transmitter, and protected from sun.

Diaphragm Seal: Typical Values

Common diaphragm materials	316L, Hastelloy C, tantalum, PTFE coated
Main errors	fill fluid expansion with temperature, capillary head

Calculators for Diaphragm Seal

CalculatorRemote Seal CalculatorFree online calculator with formula and worked example.CalculatorPressure Transmitter Elevation CorrectionFree online calculator with formula and worked example.

Frequently Asked Questions

What is a Diaphragm Seal?

A diaphragm seal isolates a pressure instrument from the process with a flexible diaphragm and a sealed fill fluid.

Why do sealed transmitters drift with weather?

The fill fluid expands with temperature and its head changes with mounting height, shifting the reading.

Can a seal be removed in the field?

No. Opening a filled system lets air in; it must be refilled under vacuum by the maker.

Learn more on the blog

Differential pressure transmitter working principle

A practical guide on instrumentationblog.in with more detail on diaphragm seal and how it is applied on real plants.

Read Full Article

More Pressure Measurement Terms

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