In Chicago, there is a bar called the Billy Goat. While there are a few locations now, the original is located on lower Michigan Avenue. With a bar that is open daily at 7 AM, there isn’t much not to like at the Billy Goat. In addition to the long bar hours, the Billy Goat is world famous for their cheeseburgers. If you order a single, you’ll be reminded with varying degrees of niceness that a double is better. Don’t argue, just get the double.
So coming off our last post on single o-ring vs. single mechanical seals, we figured we’d answer the question- is double better? As you may guess, it depends. So what are a double o-ring and double mechanical seals and when do we use them? Let’s get into it.
We’ll start with the double o-ring seal. As the name would imply, the double o-ring seal is the double version of a single o-ring seal. Available with Waukesha’s Universal 1 and Universal 3 pumps, the double o-ring seals uses a stainless-steel carrier to add a second body o-ring. The second body o-ring rides on the shaft sleeve, but because we don’t expect a large amount of product to get past the primary body o-ring, we need to add a flush fluid to lubricate the second body o-ring and dissipate heat.
We like the double o-ring seal for higher pressure applications with high viscosity products where the single o-ring seal just doesn’t hold up, but we still want to use low cost, easy to maintain seal. Typically, these applications run between 100-120 PSI discharge.
As we’ll discuss next, we also like the double o-ring seal for flush applications where we want to use a barrier fluid other than water- think chocolate or starch slurry applications. In these confectionary applications, we can’t risk getting any water into the product, but still need a heavy-duty seal to handle the higher discharge pressures and product that can be abrasive or coat. In these applications, we’ll use a product compatible grease with an automatic lubrication system that threads into the pumps flush ports to automatically lubricate the seal sleeve and body o-rings.
A double mechanical seal is also a double seal but works quite a bit differently than a double o-ring seal. We start with the same components we have with a single mechanical seal but add a second outer carbon seal and a flush fluid. We need the flush to lubricate the outer carbon seal (which ideally won’t see product) and also help lubricate and flush the primary seal faces.
It’s this cooling and lubricating of the primary seal faces that is the biggest advantage of the double mechanical seal. Not only does it allow us to run at higher temperatures, but it’s also allows to handle otherwise “un-sealable” products. Think of products that are prone to plate or are extremely abrasive. We want to remove this from the primary seal faces as efficiently as possible.
To give you an example, we’ve seen applications where a single mechanical seal will fail in sixty seconds and a double mechanical seal will run for 6+ months without issue. The double mechanical seal is also ideal for handling hazardous products that we can’t afford to have leak to atmosphere.
Drawbacks to a double mechanical seal include the complexity and cost, as well as finding a product compatible flush fluid.
So to give you a brief recap, while double o-ring and double mechanical seal are quite simply the “double” version of a single o-ring and single mechanical seal, we use them for very different applications. We like double o-ring seals for higher pressure applications where we still want a simple, low-cost seal that is easy to take apart and service. The double o-ring seal is also great for applications where plating or product coating can be a challenge, as long as we’re able to select a product compatible flush fluid. And we specify double mechanical seals for high abrasive fluids or products that tend to plate or where we know we need to run for long periods of time without disassembling the pump.
And as always, if you have any questions about double o-ring or double mechanical seals or any of your Waukesha pump needs, please contact a Triplex Sales Engineer today!