If you’ve been following this blog, you’ll have noticed that we’ve covered most every option available for SPXFlow’s industry leading lines of external circumferential PD pumps- the Universal 1, 2, and Universal 3. In today’s post, we’ll circle back to one important decision every end user needs to make for their PD pump- elastomers- and which material is best for you and your PD pump application. Waukesha PD pumps can come with either Nitrile, FKM, EPDM, silicone, Teflon encapsulated, FFKM ,or USP Class VI elastomers. But which one is right for you? While they’re all considered food grade, there’s a number of differences you should be mindful of when optimizing pump selection. Let’s take a closer look.
Nitrile (Buna, Yellow Dot)
We’ll start with the most basic Universal Pump elastomer- nitrile or more commonly, Buna. Buna, or food grade rubber, is the lowest cost elastomer available. It is what we consider the most “standard” option for the Universal 1 series of pump. Buna is rated for temperatures ranging from -30 to 200 degrees Fahrenheit, but we most commonly see it on moderate temperature applications below 130 degrees F.
Buna does not have great chemical resistance, but can work well with most fluids for a short period of time. That’s why we recommend it for Universal 1 applications where the pump is cleaned out of place and elastomers are changed out and disposed of regularly.
FKM (Viton, White Dot)
The next elastomer we’ll touch on is probably the most common one we see- fluoroelastomer or Viton. Rated for temperatures 0 to 375 degrees F, Viton is the elastomer we’d consider “standard” for the Universal 2 series of pumps which are designed to be cleaned in place (CIP). Like Buna and EPDM, Viton is an elastomer and “squishes”, making it an excellent seal. It has superior chemical compatibility to Buna and unlike EPDM (which we’ll touch on later) is compatible with oils and most process fluids we see in sanitary systems. For that reason, when in doubt, we specify Viton.
EPDM (Green Dot)
Ethylene propylene diene monomer or EPDM is another common elastomer we specify for use in Waukesha PD pumps. EPDM is comparably priced to Viton and is a great choice for low and high temperature applications (rated for fluid temperatures of -70 F to 250 degrees F).
One drawback to EPDM is it’s lack of compatibility with petroleum or oil based products. Prolonged exposure to oils can cause the EPDM to breakdown and swell.
It does, however, perform better than Viton in steam or continuously high temperature applications. For that reason, we love EPDM for hot caustic or aseptic process applications.
Silicone (Orange Color, Black Dot)
Silicone is an available option for all makes of Waukesha PD pump. Rated for temperatures ranging from -50 to 400 F, silicone has great chemical compatibility and a lower leachables and extractables profile than EPDM or FKM. For this reason, silicone is very common in pharmaceutical applications, but we see it less often in food, beverage, and personal care processes.
Teflon Encapsulated O-Rings
For ultra-high temperature applications, we also have an option for Teflon encapsulated o-rings. This option takes a standard elastomer such as silicone or Viton, and raps it in Teflon. The Teflon gives the o-ring excellent chemical resistance and allows it to perform well at temperatures up to 400 degrees F. Teflon, however, is not an elastomer- it’s a plastic- meaning it doesn’t “squish”. This makes a poor seal more prone to leaks than our elastomer options. It’s also priced at a premium to the more common elastomers Viton and EPDM. Accordingly, we only recommend Teflon encapsulated o-rings for harsh chemical applications.
We saved the most robust elastomer option we have for last. Kalrez or FFKM is the elastomer we use when we have to pull out all the stops. As an elastomer, we get excellent sealing ability and the additional fluorocarbon gives us chemical compatibility similar to Teflon. It’s the best of both worlds. So what’s the catch? You probably guessed it- cost and availability. Kalrez o-rings are extremely expensive- usually 20 to 30 times the cost of Viton or EPDM and are not widely available. Therefore, we only recommend Kalrez for the most aggressive of applications.
USP Class VI Elastomers
Our last option isn’t a different material, but rather a different classification. SPXFlow does offer USP Class VI materials in both Viton and EPDM. USP Class VI refers to a set of biocompatibility testing requirements from the U.S. Pharmacopeia whose standards inform the decision making at the Food & Drug Administration (FDA). The key word there is “pharma”- while used widely throughout pharmaceutical applications, we rarely if ever see a requirement for USP Class VI elastomers in food grade applications. But it’s important to know that they are available when the occasional pharmaceutical applications pop up.
While this may seem like an overwhelming number of elastomer options, there’s really not too much too it. Running moderate temperatures and cleaning regularly out of place? Save some money and go with Buna. Looking for a robust o-ring that will hold up for long intervals between pump disassembly, go with Viton. High temperature steam applications? EPDM will be the ideal choice there. And as always, if you have any questions about which elastomer is best for your Waukesha Universal series pump, please contact a Triplex Sales Engineer today!