In-line filters: Why use them for gas flow instruments?

February 28, 2023 Vincent Hengeveld

‘Buy cheap, buy twice’. This is never more apparent than when purchasing new flow meters or looking at ways to protect existing ones if necessary. There are various accessories that you can add-on flow meters, one of them being an in-line filter. In this blog you can read about why use in-line filters and how they work. 

In-line filters as add-on
With flow instruments, the accessory of choice often is a communication cable. These are essential in allowing you to communicate with an instrument and monitor or access the very information that you require. However, in-line filters can be far more essential to the long-term performance and life-time of your gas flow instrument.

filters, flow controller
Mass Flow Controller with In-line filter

Why use in-line filters for your gas flow instrument?

In-line filters are an essential add-on for flow instruments, particularly in industrial applications where contamination can lead to inaccurate readings, reduced performance or damage to the instrument. Although you might check your research application as well. You may think that in research applications you work with clean gases, but tiny particles can also occur here. Not only the particles in gases can be a problem, the dirt stored in the piping can be harmful as well. 

The importance of keeping the gas entering the flow instrument dry and clean cannot be overstated. An in-line filter will protect your gas flow instrument from: 
•    Debris from contaminated gas lines
•    Particles that exist in industrial gases
•    Small amounts of oil from compressors

So, do you work with ‘dirty’ gases in your process or gases with particles? Whether this is in an industrial environment or research application… the in-line filter will be your accessory of choice. 

Check our IN-LINE filters
IN-LINE filter for gas flow instrument

How do in-line filters work?

The purpose of the in-line filter is to filter the gas before entering the flow meter and to make sure that the gas is clean - without any particles. This way you avoid contamination which can lead to a number of avoidable costs. With further costs I mean costs due to down-time, service costs, calibration costs or time to remove and re-install the damaged instrument.

Besides avoiding contamination, a dry & clean gas is also crucial to ensure a better MTBF (Mean Time Between Failure) of your flow instrument. This is particularly true for flow instruments that use a bypass sensor.

The Bronkhorst flow instruments are designed for low flows and therefore have delicate and finely machined parts. This is needed to enable us to quantify the flow rates of gases that we can achieve with a good level of accuracy and repeatability. 

When you consider the potential damage that is possible from the different sources of contamination, and the delicate nature of the internal working of a flow instrument, it would appear to be a very straightforward decision to include a filter in your next purchase of a flow instrument.

'Bypass' vs 'flow-through' flow instruments

Depending on the construction, a flow instrument for gas can be more or less sensitive to contamination.  Gas flow instruments can be divided into two sensor principles:
•    Gas flow meters using the bypass principle
•    Gas flow instrument using the ‘trough-flow’ or  CTA principle (Constant Temperature Anemometry)

To learn more about the differences between these two principles, please check our knowledge base

in-line gas filters for piping

IN-LINE gas filters

Within our portfolio Bronkhorst has the IN-LINE filter available for your gas Flow instrument. These IN-LINE gas filters are easy to use. You just screw them into the inlet of the flow instrument, and it guarantees a clean gas inlet. It contains a 316L sintered metal filter cartridge that is suitable for general purpose filtration and can be cleaned with either a suitable solvent or by replacing the cartridge if heavily soiled.

If you use gas that contains large particles, we advise to use a pre-filter. A pre-filter will remove the main part of heavy particles, before they reach the main filter. 

Are you interested in more information about our technologies?

Check our IN-LINE filters Ask for advice


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Willie Snaith Road
Newmarket Suffolk CB8 7TG
Tel. +44 1223 833222
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