Why using in-line filters for flow instruments?

Why using in-line filters as accessory for your gas flow instrument?

This simple add-on to a new flow meter can protect against a multitude of issues like:

• Debris from contaminated gas lines

• Particles that exist in industrial gases

• Small amounts of oil from compressors

In-line filters are especially useful in applications where you have to deal with ‘dirty’ gases, gases with particles. This can be the case in an industrial environment, but also in research applications.  
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. 

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

Inherent to its construction, a  flow instrument for gases is more or less sensitive to contamination. In terms of construction, the thermal flow meters for gas can be divided into two sensor principles:

• Gas flow meters using the bypass principle

• Gas flow meters using the CTA principle (Constant Temperature Anemometry)

In-line filter to prevent contamination of your instrument

Preventing contamination of your gas instrument, why is this important? To increase the MTBF (Mean Time Between Failure) it is important to make sure that the gas or liquid entering the instrument is dry and clean, in particular when using flow instruments with a bypass sensor. Depending on your fluid you can select different types of flow filters. 

Our 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 mass flow instrument, it would appear to be a very straightforward decision to include a filter in your next purchase of a flow instrument.

If the gas contains large particles, we advise the use of a pre-filter. This pre-filter is recommended because it will remove a high percentage of the heavy particles, as it has a cartridge with a larger porosity than the actual filter, before they reach the main filter and reduce pressure drop from clogging and excessive maintenance/cleaning requirements.

In a previous article we have already mentioned the importance of in-line filters when installing a mass flow meter. 

“Ensure that the piping of the system is clean (before installing the instrument). For absolute cleanliness always install filters to ensure a moisture and oil-free gas stream. It is recommended to install an in-line filter upstream of the flow instrument, and if back flow can occur, a downstream filter or check valve is recommended too”. Read more tips before installation in our blog: 'Top 10 tips for installation'.