One of the things we do most often at Triplex Sales is help customers specify pumps for their sanitary process applications. We do it so often, that sometimes we take for granted the simple assumptions we make. One of the things we blitz right through is proper elastomer or soft part material selection. So in this post, we’re going to review the available elastomers for Waukesha sanitary pumps and the rules of thumb/best practices we use when choosing them.
More commonly known by it’s trade name Buna N, nitrile elastomers are the simplest, lowest cost elastomer option for Waukesha sanitary pumps. Buna is rated for temperatures of -30 to 200 F and has good overall chemical compatibility. It plays nicely with oils, weak acids, and alkalines. Temperature is what gives us the most pause and for high temperature or CIP applications, we’ll recommend other elastomers.
FKM, more commonly known by its trade name Viton, is a fluoropolymer that is rated for 0-375 F. Viton is compatible with all but the most aggressive chemicals and ideal for most food grade applications. It is the most common elastomer we specify for PD and centrifugal pumps, using it everywhere from beer pumping (due to it’s high temperature compatibility) to aggressive CIP chemicals. In fact, Viton is the standard elastomer for our in-stock PD pumps!
If there was a drawback to Viton, it’s how the material breaks down when repeatedly exposed to high temperatures, especially steam. Viton can tend to burn on to flange faces and can be difficult to remove after being steamed repeatedly. Enter EPDM. EPDM is rated for -70 to 250 F is a great alternative to Viton. Not only does it do well with high temperatures and steam, it also does well with low temperatures and has good overall chemical compatibility with everything but petroleum-based products (oils). When EPDM is exposed to oils, it swells, impacting its ability to perform as a seal. For that reason, we never use EPDM in oil-based applications.
Silicone is also an available option for Waukesha pumps. With a temperature rating of -50-400 F, one might immediately think that this would be the go to for high temperature applications. Not so fast. SPX recommends that their silicone elastomers not be used when long duration high temperature conditions are present. In these cases, FKM or FFKM are preferred. We tend to use silicone more in pharmaceutical applications due to its high purity and low leachable and extractable profile. Leachables and extractables aren’t as big of a concern in food grade applications.
Teflon encapsulated o-rings take a rubber elastomer core and extrude Teflon over it. Teflon or PTFE is the gold standard in chemical compatibility, but it’s a plastic, not an elastomer. That means it makes a lousy seal- there’s no “squish”. For that reason, we use the elastomer core to get the “squish” factor and have our Teflon make product contact so all is good. Still, it’s not as effective a seal as EPDM or FKM and we don’t often specify it.
Known more commonly by it’s trade name Kalrez, FFKM is like Viton’s big brother. It’s rated from 0-450 F and has the best chemical compatibility of any elastomer you can put in a Waukesha pump. The drawback is price and availability. Kalrez is hugely expensive (10 times or more the cost of Viton) and carries long lead times. This isn’t great for o-rings that are used as dynamic seals and often wear and need to be replaced. Use FFKM in only the most extreme applications
USP Class VI
USP Class VI isn’t so much a type of elastomer as it is a subset. USP Class VI (which will be the focus of a future post) is a designation required for many pharmaceutical applications. As most of the applications we deal in, especially on the PD side, are food grade, this isn’t as big of a concern. USP Class VI elastomers are available in Silicone, Viton, EPDM, FFKM, and Teflon (but not Buna) and must be specified at the time of order to make sure you get the appropriate documentation. In the pharma world, it’s all about the paper.
So there you have the available elastomer options for Waukesha sanitary pumps. Quick rules of thumb- for general purpose applications, Buna N will be fine. For higher temps, consider EPDM or FKM, but never use EPDM with oils. And when you need to pull out all the stops, go with FFKM. If you have any questions about which elastomer is best for your sanitary pump application, contact a Triplex Sales Engineer today!