What is the Best Seal for My Waukesha Universal 1 Sanitary PD Pump?

In today’s post, we’ll take a look at another question we get all the time here at Triplex– what is the best seal for my Waukesha Universal 1 Sanitary PD Pump? Our regular readers won’t be shocked to here our answer- It Depends. So that’s the short answer. The longer answer is what we’ll dedicate the rest of this blog to as we go through each of the seal options of the Waukesha Universal 1 PD Pump.

Single O-Ring Seal

Single O-Ring Seal

The simplest and probably most common seal option for the Waukesha Universal 1 Sanitary PD pump is the single o-ring seal. The single o-ring seal is an external seal that features a stationary body o-ring that, as the name would imply, is installed into the pump body and rides on a rotating shaft sleeve. The shaft sleeve is available in stainless, chrome oxide, and zirconia, with zirconia being the material we see most often.

The single o-ring seal is a great seal choice because it is easy to clean and to assemble. Remember- this is important because if we’re using a Universal 1 Positive Displacement pump, we’re probably taking the pump apart often to clean. This work is often done by personnel who aren’t trained to handle delicate mechanical seals. We should also point out that you don’t need a flush with a single o-ring seal.

Drawbacks to the single o-ring seal are limited pressure and temperature range. We typically only recommend using a single o-ring at pressures between 30-50 PSI and temperatures up to 180 F. The single o-ring seal will require replacement somewhat regularly and is not recommended for applications with hazardous fluids.

Double O-Ring Seal

Double O-Ring Seal

The double o-ring seal is just what it sounds like it is- two o-ring seals. To achieve this, we add an additional seal carrier that engages with the pump body to hold the second body o-ring, giving us “double” the sealing “power”. We also change the position of the shaft o-ring (to the groove closest to the shaft spline) but continue to use either a stainless steel or zirconia rotating sleeve.

While we do need a flush to reduce the friction created from the two body o-rings, the double o-ring seal is great for higher pressure and viscosity applications. It’s our go to seal choice for chocolate pumping applications. We like it for chocolate because it allows us to handle the higher-pressure differentials caused by the products viscosity we see and we can lubricate the o-ring either with a pre-charge of cocoa butter or even a slow glycol drip. Remember- to use a double o-ring seal, you’ll need to have a body that is drilled and tapped to route flush fluid to the seal.

Single Mechanical Seal

Single Mechanical Seal

So now we’ll shift to our mechanical seal options. The single mechanical seal uses a stationary seal and a rotating seat to create the seal. A variety of seat and seal materials are available, including ceramic, carbon, silicon carbide, and chrome oxide. A future post will discuss considerations for seal material selection.

We tend to see longer seal life in with single mechanical seals as they better handle a wider range of temperatures and pressures. And because we have more material selection options, the mechanical seal is a great choice for hard to handle or hazardous materials. The single mechanical seal can be used with or without flush.

So why don’t we always use a mechanical seal? There are a few reasons. First is cost- mechanical seals increase both the cost of the new pump and the replacement seal kit. Mechanical seals also require greater care when servicing. The stationary seals and the seal seats are very fragile and will break easily if dropped (don’t ask how we know that).

Double Mechanical Seal

Double Mechanical Seal

The double mechanical seal is the seal we go to when we want to pull out all of the stops. The double mechanical seal takes a standard mechanical seal and adds an additional outer seal that rides on the same rotating seal seat. It’s called the “outer” seal because it rights outside the inner seal on the rotating seal seat. Because we have 2 seal faces on the seal seat, we will need a flush to dissipate the heat created by the additional friction.

As mentioned before, the double mechanical seal is the one we go to when we want to pull out all of the stops. So what kind of applications are those? Think hazardous fluids, abrasive slurries, high pressure pumping of chemicals or resins. Things like that.


So there you have it- an overview of all of the seal options in the Waukesha Universal 1 Sanitary PD pump line Which one is best? Well that depends on your application. But in general, either a single o-ring or single mechanical seal will cover about 85% of your pump applications.

In future posts, we’ll take a look at both the Universal 2 and Universal 3 PD pump seal options as well as do a deeper dive on seal material selection criteria.

Until then and as always, if you have any questions about your Waukesha Universal Positive Displacement pump, contact a Triplex Sales Engineer today.

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