Single Mechanical vs. Single O-Ring Seal- What’s the Difference?

One of the most common inquiries we get is from customers looking to convert their Universal 1 pump from a single o-ring seal to a single mechanical seal. One of the differentiating features of the Universal Series of pumps from Waukesha Cherry Burrell is the ability to change the seal and material configuration quickly and easily for the solution that gives the best balance of cost and performance. So when should you use a single o-ring seal and when should you use a single mechanical seal? Let’s take a closer look.

Single O-ring Seal Components

The standard, out of the box seal for the Waukesha Universal 1 is the single o-ring seal. The beauty of the single o-ring seal is its simplicity. The single o-ring features three main parts- a shaft sleeve, a body o-ring, and a shaft o-ring. The sleeve acts as our rotating face and is held in place by a pin on the shaft. The shaft o-ring prevents product from getting under the sleeve. And the body o-ring, our stationary seal in this case, rides on the shaft sleeve and seals product in the pump cavity.

The single o-ring seal is a great seal for lower pressure applications with clean lubricating fluids. It’s also great for applications where the pump needs to be torn down and cleaned regularly. O-rings and sleeves are cheap and not very sensitive to handling. The most common wear item is the body o-ring, which we typically see changed weekly along with the shaft o rings. The telltale sign of a worn body o-ring or high-pressure operation is a flat spot in the o-ring- that’s typically how product gets past it. The sleeves are reversible and tend to last longer.

While the single o-ring seal is simple and low cost, it’s not particularly robust. And changing the seal on the U1 also requires removing the pump body. Not a huge deal for U1 18 that is easily accessible, but a much bigger deal for a U1 220 that is located underneath a tank. Having to change that 220 seal every week is going to get old, fast.

Single Mechanical Seal Components

For that reason, many customers call us and ask to change to what they consider to be a “superior” single mechanical seal. The single mechanical seal has five main components- a stationary steal, a rotating seal seat, a body o-ring, a shaft o-ring, and a wave spring. The rotating seal seat engages with a pin on the shaft while the stationary seal aligns with a pin on the pump body and is “loaded” onto the seal seat by the wave spring. The body and shaft o-rings support the seal and seal seat by preventing leakage past them.

When the pump is running, fluid pressure in the pump head forces the two faces closer together while providing the seals with a lubricating film, reducing frictional wear across the faces. While this lubricating film would be considered leakage, the frictional heat generated causes the fluid to evaporate. The combination of a close seal face gap and reduced friction allows our single mechanical seal to operate at much higher pressure and temperatures for longer periods of time (assuming the correct combination of sealing materials is selected).

While the single mechanical seal is certainly more robust, we don’t necessarily consider it “superior” to the single o-ring seal. The single mechanical seal is much more expensive to service, requiring more parts, and careful handling.

For that reason, at Triplex, we don’t always recommend a specific seal, we use our experience to work with our partners to get the right seal for their application. If you’re pumping a clean, lubricating fluid at relatively low temperatures and pressures and are already pulling the pump apart for service anyway, an o-ring seal will work just fine. If you’re application is more demanding, handling hot, abrasive products at higher temperatures and pressures or when regular maintenance is less than ideal, we recommend a mechanical seal.

As always, if you have any questions about which seal is best for your Universal series pump or any other high purity processing needs, please contact a Triplex Sales Engineer today!

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