In today’s post, we’re going to continue our focus Waukesha Universal Pump seals and look at another lesser-known seal option- narrow face seals. So what is a knife or narrow face seal, how does it work, and sort of applications do we applications do we recommend it for? Let’s get into it.
To start, what is a narrow face seal? Narrow face or knife seal uses a narrow face width to provide a high unit loading to break through thick product films and residue. The narrow face is for the stationary seal only, so we still use standard rotary seal seats.
Narrow face seals first came to be when a Waukesha pump user was having trouble pumping acetate dope using a single seal. Pressure spikes in the system would force the product between normal with seal faces. Accordingly, the seal faces could not close and the seals would start leaking. When narrow face seal were implemented, their “knife-like” edge would cut through the product and maintain the seal.
Narrow face seals are also good for applications where product has the possibility of settling during down time and sticking to the faces. This basically bonds the stationary inner seal and rotary seal seat together, and on startup, something has to give, often resulting in seal faces shattering. In this application, the narrow face seal provides less surface area for product to build up, reducing problematic startup issues.
The final application we’d like to highlight as a good fit for narrow face seals are applications where products tend to plate or coat and we don’t want to use a flush. Think chocolate applications. The bane of confectioners is getting water in their product. But because chocolate tends to plate or coat seal faces, we usually recommend either a double o ring seal in a Universal 1 or a double mechanical seal in a Universal 2. The challenge with a double seal is the required flush. With products compatible with water, this isn’t an issue, but as we mentioned, chocolate hates water. So we often have to use alternative barrier fluids, like cocoa butter or propylene glycol.
As an alternative, we also recommend knife seals in chocolate applications. As the chocolate tends to plate on the seal faces, the higher point loading and leading edge of the knife seal cuts through the chocolate, allowing the seal faces to stay together and do their job.
For Universal 2 pumps, narrow face seals are only available in tungsten carbide. For the Universal 3, narrow face seals are available in tungsten carbide, as well as silicon carbide and carbon.
So the next time you’re running a product that plates or coats or have a process where pressure spikes may force the seal faces apart, consider using a knife or narrow face seal. And as always, if you have any questions about which seal is best for your Waukesha Universal Pump, contact a Triplex Sales Engineer today!
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