You have an application that requires a sanitary PD pump.  You decide you want to go with Waukesha. Who wouldn’t?  They are the kings of sanitary PD pumps.  You now have to decide on which model, the U1 or the U2.  Which is the better choice?  It depends on your application. In this post we will go over the criteria we use here to determine which is the better choice.

Waukesha Universal 2

What They Have in Common
On the surface both these pump have a lot in common.  They both have ECP (external circumferential piston) style rotors, rendering them very efficient, with very low slip characteristics.  Their range of sizes are also almost identical allowing both models to cover a wide range of different flow rates.  Their fluid displacement per revolution is almost identical with like for like models. To the untrained eye, they visually appear nearly identical. So what’s different?

The Waukesha Universal 2 pump is designed to be cleaned in place. The Universal 1 is not.  The biggest difference is that the U2 rotors have rotor seals that prevent fluid from getting between the rotors and the pump shafts.  The shafts on the U2 have o rings to seal the front and back of the rotors and the rotor nut has an o ring that seals it to the front of the rotor.  The U1 rotors slide onto the pump shaft without o rings.  The rotors are locked in place by a dual jam nut configuration that has no seals. The U2 rotor nuts have to be torqued down with a torque wrench to ensure proper performance. The U1 jam nuts need only be fastened with a crescent wrench.

The Universal 2 pump is also has an option for a flat body profile design, making the pump fully drainable when the ports are mounted in the vertical position.

Additional options available exclusively with the Universal 2 model include special CIP and CIP w/ particulate models that include flat body profiles as standard and perforated rotors that aid with cleaning. While perforated rotors decrease efficiency, the ultimate goal, cleanability, is enhanced.

So if you plan on cleaning the pump in place, go with the U2.  If you plan on disassembling your pump and cleaning it manually, the U1 is a better choice.  By design it is easier to disassembly and reassemble with fewer tools.

Seals
The Waukesha U1 pump gives you a choice between a simple, inexpensive o ring seal and both single and double mechanical seals.  The U2 offers only mechanical seals.  O ring seals, while cheaper to replace, normally do not have the life expectancy of a mechanical seal.  But they are easy to change and if you plan on regular disassembly of the pump for cleaning they can be a cost effective choice, putting you again in the U1 camp.

If you want mechanical seals, the U2 pumps have a most robust seal design and in difficult seal application may give you less trouble.  The Universal 2 mechanical seals, while offering the same single and double mechanical styles of the Universal 1, also offer high pressure barrier and narrow face options. Both of these options are designed for abrasive, tough to pump materials, such as acetate dope, xanthan gum, and lime slurry. These seal options make the Universal 2 an excellent option in systems where pressure spike force product between seal faces and cause leakage.

Pressure Ratings
For most sizes, Waukesha Universal 1 maximum pressure rating is 200psi.  Many sizes of the Universal 2 have ratings of 300psi, some over 400psi.  Why is this?  The sanitary U2 pumps have 17-4 alloy shafts as standard. The U1 standard shafts are 316 stainless steel.  316 is a more brittle material than 17-4 making it more likely to fatigue more quickly under the stresses and high radial loads of higher pressure applications.  17-4 shafts are offered as an option on the U1, but with a cost adder. Universal 2 shafts are also larger than Universal 1 shafts, again increasing performance with in demanding applications with high torque requirements.
The Waukesha Universal 2 series of pump also come standard with acorn cover hex nuts and body retaining screws, as opposed to the Universal 1’s standard wing cover nuts. The acorn hex nuts also have a torque spec and enable the Universal 2 to outperform the Universal 1 in high pressure applications. Body retaining screws also help deter shaft deflection.

It’s worth noting that pressure ratings of these pumps are based on engineering calculations and endurance testing by Waukesha and have been used satisfactorily at differential pressures beyond their catalog rating on occasion. This should be dealt with on a case by case basis.  That being said, if high pressure is an issue, you should probably be in the U2 camp.

Waukesha Universal 1

Cost
Over the entire size range the base Waukesha U1 is about 13%-17% less expensive than the U2.  If you add mechanical seals to the U1 it is about 9%-10% cheaper.  Add the 17-4 shafts with mechanical seals and the U1 is about 7%-9% less expensive, depending on the size pump.

Other Considerations
We have found the Waukesha U2 to perform better in applications where you are pumping highly viscous material that tends to set up if the pump is idle.  In cases like this material can set up around the rotor nuts on the U1 and occasionally force them loose upon startup.  There are fixes for this, but the U2 pump virtually eliminates this phenomenon. Seal flushing arrangements with the U2 are also simplified, requiring only one inlet and outlet to flush both seals as opposed to the (4) port configuration on the Universal 1. The U2 body has a machined port that allow flush media to reach both the upper and lower seal faces.  As discussed previously, the U2 mechanical seal design is more robust, lessening the possibility that the seals can crack on startup if you are pumping sticky material that can adhere to the seal faces.

Summary
These are both excellent pumps.  We have found that the easiest way to determine the proper choice is to take an in depth look at the application.  After sorting through the different aspects of the application the choice usually becomes pretty simple.  In a nutshell, if you are planning to regularly disassemble your pump for cleaning and your application is not particularly high pressure (less than 200psi), the Waukesha Universal 1 should be an excellent, cost effective choice.  If you plan to run the pump for long continuous periods, want to clean it in place or have higher pressures, the Waukesha Universal 2 is probably the way to go.
There are many smaller differences to these two sanitary pumps, but we think we have covered the biggest issues.  Hopefully this post has answered some questions.  If you have more, contact us via our website or call us at 800-800-8486.  We apply Waukesha sanitary pumps everyday.