Sealing the Un-sealable- What a Double Mechanical Seal & Flush Can do for You

As we’ve mentioned before in this blog, an expert is just a person who has made every imaginable mistake in a given field. And as we’ve also mentioned, we sell hundreds of Waukesha PD pumps every year. For 98% there are absolutely no surprises- we specify the pump, customer installs the pump, the customer is happy with the pump. Occasionally, however, there’s a surprise. We recently helped a customer through an application handling a water-based coating that was one such surprise.

The application started the same way most others do- we receive a call looking for a Waukesha PD pump. The customer was handling a low viscosity aqueous based coating, pumping short distances with little discharge head. They had previously been using a progressive cavity pump and were not happy with the performance and maintenance costs. No red flags yet.

So Triplex Sales engineers sized the pump, using our “standard” seal configuration for a Universal 2- single mechanical seal (silicon carbide vs. silicon carbide) with Viton elastomers. The customer ordered the pump and turned around the complete assembly in about 3 weeks.

When a pump leaks, everyone wants to watch.

Then the issues started. Immediately upon start up, the pump started leaking. Not after a few runs, immediately. Because we stand behind every product we sell, we returned to the customer’s facility to see what was going on.

Turns out this product tends to coat out, especially when it sees heat. This had created issues with the progressive cavity pump- while it would seal because they were using a gland type packing seal, product would coat the stator and cause wear. Because we didn’t want to have to go straight to a flush, we decided to try knife edge or narrow face tungsten carbide seal (you can learn more about knife edge seals in this post).

Those aren’t cracks- product plating on seal seat.

When we started up with the narrow face seal, there was good news and bad news. The good news was that the knife seals lasted 100% longer than the standard silicon carbide seals. The bad news was that this was still only about 75 seconds of run time before leaking.

So what did we do? We then installed a carbon outer seal and seal flush lines. And voila, no more seal leak. So what does that carbon seal and flush do that makes it so effective with hard to handle products? The seal flush in this application served three purposes to help make the product pumpable. A seal flush will:

  1. Eliminate air- the product will not see atmosphere
  2. Provide lubricity by flushing and cleaning seal faces
  3. Dissipate heat
Inner tungsten, outer carbon seal shown above

For this application, lubricity and heat dissipation were the two we needed most. While the product is liquid when open to atmosphere, as soon as it sees friction and heat, it starts to plate out. And once it starts plating, it’s like a chain reaction that ends in seal failure. So the seal flush helped to not only dissipate heat, but lubricate and clean the seal faces to prevent the plating from starting. This customer is now able to run leak free 24/7, 365.

So the next time you have a hard to handle product, consider a double mechanical seal with flush. This seal configuration will isolate product from atmosphere, provide lubricity to the seal faces, and dissipate heat. And as always, if you have any questions about which seal to use in your Waukesha Universal Series PD pump, contact a Triplex Sales Engineer today!

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