In our last post, we focused on everything but the front-loading seal in a Universal 3 pump. In today’s post, we’re going to take a closer look at the hallmark feature of the U3- the front-loading seal. When presenting the U3 to skeptical maintenance and engineering folks, the most common objection we get is, “well when that seal fails, it’s going to get into my product”. In today’s post, we’re going to take a closer look at that objection and illustrate why that isn’t something you need to be concerned with.
Let’s start by taking a closer look at the front-loading seal feature itself. A Universal 3 takes the traditional rotor design and basically turns it backwards. Instead of the rotor hubs extending into the cover, the design is inverted, with the hubs located on the cover extending over the pump shaft. This allows us then to locate the rotating seal component (either a the seal face or seal sleeve) in the back of the rotor. The stationary seal is then loaded directly into the back of the body. This means that for single o-ring, double o-ring, single mechanical, and double mechanical style pumps, we’re able to replace the primary seal components without removing the pump body. This is a huge time savings, especially for larger pumps or pumps located in difficult to service locations- like under a tank.
Looking at the pump with the cover off, you can see that while the seal is in the product zone, it isn’t exactly getting a lot of exposure, so let’s take a step back and review what we know about mechanical seals- we can’t have them running dry.
Whether you have a chrome oxide sleeve running on a Viton O-ring or a silicon carbide seal face running against another silicon carbide seal face, we’re going to generate a considerable amount of friction and heat. To dissipate this heat, we need to have some sort of flush media on this. It could be water, but in a single seal configuration, more commonly it’s product. And the U3 seal design is no exception- we have to ensure we get product to the seal faces.
In order to accomplish this, there is a very small flat machined into the rotor hub to help encourage flow to the seal faces, especially during cleaning. In fact, for high viscosity products, there is even a “particulate” rotor option with two flats to allow even more flow to the seal faces.
So what happens when the seal in a U3 breaks? Well, like most things in life, it will follow the path of least resistance- failing to atmosphere, not into the pressurized product zone. Lab testing by SPXFlow and our field experience confirms this- when insulted, the U3 seal fails to atmosphere, not into the product.
And now let’s take an even more practical look at it. In order to get into the product, the seal would have to make its way around the rotor and through the narrow flat, which we measured at 0.025” on a U3 130 pump. Check it out for yourself in this picture. So when that rotor is spinning at the typical 250-400 RPM, that is quite the tortuous path.
In short, don’t worry about it. The U3 seals, like most things in life, will follow the path of least resistance and fail to atmosphere, allowing you to rest easy and service your pump even easier.
As always, if you have any questions about any of SPXFlow’s Universal series pumps, please contact a Triplex Sales Engineer today!