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To Teflon or Not to Teflon?

That is the question.

Over the last few years, we have received a lot of requests for Teflon (PTFE) diaphragms. Because of its chemical neutrality, Teflon is a well-known material that is used frequently in bioprocessing/pharma applications. Until relatively recently, ASEPCO did not have a Teflon diaphragm option, but now we provide PTFE diaphragms for our 1.0, 1.5, 2.0, and 3.0-inch Radial-Diaphragm™ tank valves.

Tank Bottom Valve with PTFE diaphragm

ASEPCO Radial-Diaphragm Tank-Bottom Valve with PTFE Diaphragm

Despite the fact that we have PTFE diaphragms, we hope that only a small percentage of our customers will use them. Why?

  • Teflon is not an elastomer, and as a result, it doesn’t seal as positively with the valve as the elastomeric diaphragm materials that we provide. In addition, Teflon’s tendency to cold flow away from pressure in contact zones is well known, and this characteristic can lead to lower sealing pressures over time.
  • Because Teflon doesn’t create a highly positive seal with the valve, it doesn’t perform well under high process pressures.
  • Maintenance is more time consuming and requires a bit more care to ensure the best diaphragm seat possible.
  • Teflon diaphragms are more costly.

It has been our experience that Teflon is an especially poor choice when:

  • Process temperatures are below freezing.
  • The pressure at the valve exceeds 75 PSI.

If we don’t want most of our customers to adopt them, why do we offer PTFE diaphragms? Well the fact is, under certain circumstances, they are the best choice—maybe even the only choice. What are those circumstances?

  • Exposure to extreme chemicals: When the process exposes the diaphragms to extremely caustic chemicals, such as heptane or methyl chloride, Teflon is the right choice.
  • Extreme exposure to steam: If the process subjects the diaphragms to several hours of steam exposure per day, Teflon is the right choice.
  • Extreme exposure to heat: If the diaphragms are going to be exposed to heat in excess of 135°C, Teflon is the right choice.

We believe that in most situations, we have a diaphragm material that performs as well as or better than Teflon at a lower cost. We provide seven other materials that have varying resistances to chemical, steam, and heat exposure. The table below might give you an idea of what other materials you should consider for your particular process.

Diaphragm family

ASPECO’s Diaphragm Family

Material Acceptable Temp Range Features
Silicone -60 to 275°F
-51 to 135°C
Low cost
Physically resilient
Silicone Plus -60 to 275°F
-51 to 135°C
The same features of Silicone, but twice the longevity
Moderate cost
EPDM -60 to 275°F
-51 to 135°C
Widely used in pharmaceutical apps
Low cost
Fair chemical resistance; should not be used with solvents or petroleum agents
EPDM Plus -30 to 275°F
-35 to 135°C
Similar properties to EPDM, but twice the longevity
Not sticky, easier to remove from valve
Moderate cost
Viton A -4 to 392°F
-20 to 200°C
The most commonly used version of Viton
Should NOT be used with most ketones or esters
Should not be used with steam
Moderately expensive
Viton A (SR) -4 to 392°F
-20 to 200°C
Steam-resistant version of Viton A
Performs well in conditions with extended steam
Strong chemical resistance
Expensive
Viton GF -4 to 392°F
-20 to 200°C
More chemically resistant than Viton A
Offers good steam resistance
Should not be used with most ketones or esters
Expensive
PTFE 32 to 500°F
0 to 260°C
Extremely chemically resistant, often used with heptane and methyl chloride
Extremely steam resistant
Cold flow issues that can result in leaking
Only available for tank valves and very expensive

If you have a truly extreme situation, contact us about our new PTFE diaphragms; however, if your process is not extreme, join the growing group of our customers who are using our EPDM Plus and steam-resistant Viton A diaphragms for their relatively challenging situations, often at a significant cost savings over PTFE.

For information about how our customers go about selecting diaphragm materials, see the article at http://asepco.com/2012/07/diaphragm-selection/.


Note: Please use the information in this article as a general indication of the differences between the materials. Do not use this information alone to determine if a diaphragm material is right for your process. Before using any diaphragm in a process, you should verify its compatibility with an elastomer or materials expert.

For more information about the chemical compatibility of these materials, refer to the Cole-Parmer Chemical Compatibility database at http://www.coleparmer.com/techinfo/ChemComp.asp.

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