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Sanitary Pump Seals Revisited- Handling Lime and Molasses, A Couple of Case Studies

December 12, 2013

A few weeks back we discussed the general operating principles of a mechanical seals for sanitary pumps and gave an overview of materials. In this post we are going to take a look at two specific sanitary pump applications Holland ran into with customers in the field and how we helped them get better life out of their pump seals.

Molasses Handling

Molasses, a high sugar product, poses some pretty significant seal issues. Recently, we had a customer who was opening a new facility. Operators had found an aftermarket pump they decided to use for their new facility. Because this pump was not originally configured to handle molasses, they quickly ran into problems.

Products that crystallize, such as molasses, sugar, caustics, and brine, tend to clog seal faces on the atmospheric side of seals. This face build up occurs when the product passes along the faces and the moisture vaporizes the fluid. Over time, the crystals will continue to build up and restrict the seal’s ability to adjust for movement, stalling o rings and clogging springs. The crystal build up is also very abrasive and causes rapid wear of the faces.

To combat this, hard seal faces are suggested. Harder seal faces generate a lot of heat (an enemy of pump seals), so the use of a flush and drain is critical. The quench not only helps control temperature, but also cleans debris from the atmospheric side of the seal.

Ideal face materials in sugar applications are hard, like silicon carbide or ceramic. If it is a high pressure differential application, a double seal with high pressure flush is also suggested.

So how did Holland help this customer? First, we had them send their pump in for a complete seal overhaul. We cleaned and degreased the pump and then tapped drilled flush ports in the body. While Waukesha Universal 2 pumps do not come standard with flush ports, their bodies do come standard with flush canal. This allows Holland to modify pumps to accommodate a flush after market, even on pumps as big as this U2 220 (good luck finding someone else with the technical knowhow AND a drill press large enough to accommodate that big of a pump body).

Holland Sanitary Pump Repair Facility

Holland Sanitary Pump Repair Facility

After tapping and drilling the flush ports, we installed silicon carbide seats and seals to better handle the abrasive molasses. We also supplied the customer with all auxiliary components, including a needle valve, quick connectors, simple water lines, and even a garden hose adapter so when they got their pump back, flush set up was plug and play.

Lime Slurries

In the tortilla chip production, lime slurry is used to soften the corn skins prior to milling and grinding into masa, a thick corn meal like paste that is baked or fried, to make corn chips. Lime is highly alkaline: the alkalinity helps the dissolution of hemicellulose, the major glue-like component of the maize cell walls, and loosens the hulls from the kernels and softens the corn.

The same alkalinity that helps with nixtamalization, also wreaks havoc on pump seals. In a lime slurry, calcium oxide particles are suspended in solution. These particles are jagged and abrasive. Because it is a solution, lime is able to get between small cracks, crevices, and voids, such as the micro gap in a mechanical seal. When this happens, the lime changes to a solid mass in a phenomenon known as “scaling”. Scale leads to extremely rapid seal failure.

When Holland went to visit this application in the field, this phenomenon was overwhelmingly apparent. With some detective work, we were able to find out that for the past 18-24 months, there had been almost no issues with this pump. Then the seal failed. No big deal, their mechanics changed it out and put it back into service. About 6 months later this time, it failed again. Ok, this is started to become a trend. After the second seal replacement, the seal failed again within a week. Now we have an issue.
So what happened and what did we do to fix it? Well, the solution was twofold. The Waukesha U2 Model 15 in question was originally sold with a ceramic vs. ceramic single mechanical seal. After the first seal failure, mechanics installed a new carbon inner seal to go along with the ceramic seal seat. While carbon is excellent for dissipating heat, offers good lubricity, and is a good fit for many applications, it is not a good fit for lime slurry.

When handling slurries, especially abrasive slurries like lime, hard faces, like ceramic are essential. Soft surfaces, like carbon, just don’t cut it. Ideally, a double seal with a flush would be used when handling a slurry, but for this application, simply getting back to the ceramic vs. ceramic seal was enough.

But what about the second half of the problem, why did the pump, after originally installing a carbon seal, run for 6 months, while the second carbon seal only lasted a few weeks? Well, over time this user had misplaced many of the Universal 2’s original cover studs. These, along with the acorn hex nuts, had been replaced with simple hex bolts. As we’ve previously talked about in our posts on the Waukesha Universal 2 sanitary pump, not only do the rotor nuts have a torque spec, but the cover nuts do as well. Making sure the pump is properly assembled and torqued is critical to making sure all parts work cohesively, including the seals. What we believed happened is without proper torque, lime was able to more readily get between seal faces, leading to scale and rapid failure.

Conclusion

So the next time you are having trouble with your pump seals or need to specify a seal configuration for a new application, give us a call or contact us via our website. At Holland, we have been putting pumps into industrial and sanitary applications for over 60 years. Leverage our knowledge and let us help you make the best decision for your fluid handling needs.

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