Selecting your flow meter
Before selecting your flow meter, it is important to think about the chemical resistance based on your application. This is relatively easy when the instrument is dedicated for measuring only one gas, but it can be more challenging when the flow meter is used to measure multiple gases. In the latter case, you have to check the compatibility of each gas separately.
If you want to learn more about mass flow meters and mass flow controllers, check our knowledge base page "Thermal mass flow measurement"
Choice of your elastomeric seal
It is best to base the choice of the elastomeric sealing material of your flow meter on the chemical resistance at operating conditions. Through the years, we have gathered a lot of information about the compatibility of various compounds, and we can advise you accordingly.
FKM or FPM (Viton®) – elastomeric seal
In many applications a general elastomeric seal, such as FKM or FPM flouroelastomer, is used (also known as Viton®).
In-depth information: FKM is short for fluoroelastomer according to the American standard ASTM. FPM is the international abbreviation according to DIN/ISO and Viton® is the registered trademark of DuPont Performance Elastomers.
This type of elastomeric seal causes limited chemical compatibility issues. However, the chemical resistance of the used elastomer is not always compatible with the chosen gas in your process. So, please check this on forehand.
As mentioned before, FKM and FPM are used in many different applications. Besides these, you can also choose to use:
- FFKM or FFPM (Kalrez®)
- EPDM
In-depth information: FFKM is the term used according to the American ASTM 1418 standard, whereas FFPM is the equivalent in the ISO/DIN 1629 standard. Both are perfluoroelastomeric compounds. These compounds contain a higher amount of fluorine than the above mentioned fluoreolastomers. EPDM is Ethyleen Propyleen Dieen monomeer.
Plunger Swell
For mass flow controllers, swelling of the elastomer material can be a problem. A mass flow controller is in fact a mass flow meter fitted with a control valve. The plunger of the valve connected to the flow meter, is made of elastomer material. The lift of the plunger during activation is very limited. You can hardly see it; it is only a few micrometers. You can imagine that swelling of the plunger may affect the ability of the valve to function correctly.
Body & sensor material for your flow meter
Besides the choice of sealing, you also should consider the body and sensor material of your flow meter. Stainless steel is a common material used for the body and sensor, but applications with aggressive chemicals may require a Hastelloy sensor, or a sensor coated for higher chemical resistance.
Flow meters without elastomeric seal
Not all flow meters contain an elastomeric seal. In our product portfolio we also have a Coriolis based product line. These flow meters do not contain an elastomeric seal. This is not necessarily due the construction of the sensor.
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