While oversized everything and cowboy cosplay (thanks a lot Yellowstone) are all the rage in fashion for 2023, internal seals on both centrifugal and positive displacement pumps have taken the high purity processing space by storm. While we love internal seals for their maintenance savings and advantages in some high temperature, sticky, or abrasive applications, there are some applications where they aren’t the best fit. We’ll take a closer look at those applications in this post so you can make the most informed decision for your pump application.
High Touch Mechanical Seal Applications
The first application where we find some challenges with internal seal are what we’ll call “high touch” mechanical seal applications. These are applications where the pump head or cover is frequently removed and the rotors are pulled for cleaning. This is very common in meat processing applications that still require daily tear down and swabbing.
The great part about an internal seal is that, as the name would imply, it is internal and in the product zone. The downside of that is that when the rotors come out, maintenance folks are directly handling the seals. This isn’t a big deal if you’re using a Universal 3 with a single o-ring or double o-ring seal, but if you’re using a ZP3 or Duracirc with mechanical seal, it can create problems. Mechanical seal faces are very fragile in nature and we want to minimize handling wherever possible. So in applications where we know that the rotors are coming out often, we’ll stick with a traditional external seal.
Rotor Removal for CIP
Along the lines of the high touch applications we touched an above, another application we see all the time (even though it’s usually not necessary) are applications where customers pull the rotors for CIP. There are a few reasons why customers opt to do this, usually to promote flow through the pump, even though it is not required to effectively CIP a Universal 2 or Universal 3 PD pump.
The problem here (in addition to being a “high tough” application) is that with most front loading seals the rotary seal is located in the rotor! So if you take the rotor out, you don’t have a seal and your pump is going to leak out the back. So this is clearly an application where we’ll want to use an external seal.
Ultra-Critical Process Applications
The last application where we’ll want to strongly consider if an internal seal is a good fit is ultra-critical process applications. These are usually downstream applications where the only thing standing between the product and consumer is packaging. It could also be an application with very sensitive equipment, like Coriolis meters or tangential flow filter membranes.
While we’ve posted specifically about why you don’t need to worry about your U3 internal seal failing into your product (and you really don’t), there are other centrifugal pump internal seal designs where there is a high risk. So for these applications, we may want to stick with an external seal.
In closing, while internal seals have been an excellent innovation now being offered on centrifugal, PD, and twin screw pumps from a number of manufacturers, there are still some applications that will benefit from a good old external seal. If you’re wondering if an internal seal is right for your application, please contact a Triplex Sales Engineer today!