Pressure Measurement · Glossary

What is Fill Fluid?

liquid inside sensors and sealsPressure Measurement

Fill fluid is the incompressible liquid inside a pressure sensor or diaphragm seal that transmits pressure to the sensing element.

Fill Fluid Explained

Fill fluid is chosen for the process temperature, vacuum, compatibility and hygiene. Its density and thermal expansion set part of the seal error.

Oxygen and chlorine service need inert fills, since hydrocarbon oils can react violently. Food service uses fluids approved for incidental food contact.

Fill Fluid: Typical Values

Silicone oil	general purpose
Inert (halocarbon) fluid	oxygen and chlorine
Food grade oil	sanitary service
High temperature silicone	hot and vacuum service

Calculators for Fill Fluid

CalculatorRemote Seal CalculatorFree online calculator with formula and worked example.

Frequently Asked Questions

What is Fill Fluid?

Fill fluid is the incompressible liquid inside a pressure sensor or diaphragm seal that transmits pressure to the sensing element.

What happens if the fill fluid leaks?

The sensor reads wrong or not at all, and the process can be contaminated. The unit must be replaced or refilled by the maker.

Why is fill fluid density on the data sheet?

It is needed to calculate the capillary head for elevation and zero correction.

Learn more on the blog

Differential pressure transmitter working principle

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

Read Full Article

More Pressure Measurement Terms

Pressure termPiezoresistive Pressure SensorA piezoresistive pressure sensor uses resistors on a diaphragm whose resistance changes with strain as…Pressure termCapacitive Pressure SensorA capacitive pressure sensor measures pressure from the change in capacitance as a diaphragm moves…Pressure termManometerA manometer measures pressure from the height difference of a liquid column in a U tube or inclined tube.Pressure termWater HammerWater hammer is the pressure surge created when a moving liquid is suddenly stopped, for example by fast…Pressure termPressure SnubberA pressure snubber is a restriction fitted before a gauge or switch to damp pulsation and pressure spikes.Pressure termPressure Gauge SiphonA pressure gauge siphon is a looped or U shaped tube fitted below a pressure gauge on steam to keep hot…

All pressure measurement terms · Full glossary A to Z