Niels Bohr once said, “An expert is a person who has made all the mistakes that can be made in a very narrow field”. As the Midwest’s leading expert in Waukesha Positive Displacement pumps, we’ve been sizing and applying Waukesha positive displacement pumps for over 40 years. And contrary to popular belief, we have made a mistake or two in that time. Fortunately for our partners, we’ve learned from them and are now on a mission to share those learnings with you. In today’s post, we’ll touch on a few of the most common Waukesha pump sizing mistakes we see every day.
Over Speeding
Over speeding- or under sizing- pumps is probably the most common mistake we see made when sizing a PD pump. Just because a website says your Waukesha Model 60 can give you a nominal capacity to 90 GPM and has a maximum speed of 600 RPM doesn’t mean that’s a good idea.
As a general rule of thumb, we like to keep pump speeds between 250-400 RPM, even if that means going up a pump size to run slower. The Waukesha pump was designed specifically to handle high viscosity products, but the pump can’t move what isn’t there. So we want to give product time to get into the pump.
If we run the pump too fast, we risk cavitation. And with high viscosity products- like shampoos, heavy syrups, and pumpkin purees, we’ll want to run even slower- maybe 75-150 RPM to give the product time to keep the pump suction flooded.
Series Selection
One of the first questions we ask food manufacturers and processors when they come to us with a new pump application is, “how are you going to clean the pump?”. We ask this so we can get users into the correct pump series or evaluate their existing process. I can’t tell you how many people have told me they CIP and run a Waukesha U1 with o-ring seal.
Remember- the Universal 1, with it quick knockdown features like winged cover nuts and rotor jam nuts, and simple o-ring seal options, is designed to be cleaned out of place.
The Universal 2 series of pumps, which requires a torque wrench to assemble and features options like flat body profile for drainability, standard mechanical seals, and CIP rotors, was designed specifically for clean in of place processes. This is not the pump you want to be taking apart every day.
The Universal 3 is the best of both Universal 1 and Universal 2 worlds. Designed for CIP, standard features include stainless steel gear case, flat body profile and mechanical seals, but also has optional o-ring seals for quick, easy maintenance. And all seals are front loading, meaning they can be serviced without removing the pump body.
Turndown
We dedicated an entire post to sizing pumps for high turndown applications (you can read that post here) and bring it up again here because everyone screws this up. Remember- if you’re using a VFD to reduce the speed of a pump, as you reduce speed, you will lose horsepower. The key here is to “split the difference” on duty points- overspeed for your high flow and slow it down for your lower speed applications. And most importantly, re-read our post on sizing for high turndown applications.
Feature Selection
This one is kind of a catch all- feature selection. We touched on some common features above. If we know we’re putting a pump into a washdown environment and are using a stainless steel gearmotor, we should spend the additional $200-$500 and get a stainless steel gearcase for our Universal pump as well.
The next feature we often see issues with is rotor clearance. For the Universal 1 and Universal 2, the standard rotor clearance is for low viscosity fluids with optional hot clearance or extra hot clearance rotors to allow for higher temperatures. On the Universal 3, the standard rotor clearance is hot clearance, with optional low viscosity or extra hot clearance rotor options.
The reason for this is that for products above say 500 centipoise (i.e. most of what gets pumped with a Waukesha Universal series pump), they’re thick enough that we don’t see much slip even at ambient temperatures. For that reason, we recommend using a hot clearance rotor as standard in most Universal 1 and Universal 2 applications as well.
Wrong Pump for the Job
Sometimes, the Universal series of ECP pumps just aren’t the right pump for the job. Occasionally, we’ll see customers hell bent on putting in a Waukesha Universal pump. They use them everywhere else in the plant, why can’t they use it to stuff their spray dryer with 800 psi?
If you’re pumping low viscosity fluids, a centrifugal pump is fine. Going to be running dry for extended periods, pumping out of a drum or dead heading the pump consistently? Consider an AODD pump. Exceptionally low flows? Think about a peristaltic. Just because it’s the can-do pump, doesn’t mean that occasionally there another pump that can-do-better. So avoid getting too locked in to any one pump.
To wrap up this post, keep in mind these 5 mistakes we see people make all too often. Always remember to run your pump nice and slow. Use a Universal 1 for COP, Universal 2 for CIP, and run, don’t walk to demo the new Universal 3. Revisit our post on high turndown applications and be mindful of all the features and options available on the Waukesha Universal series. And as always, if you have any questions about sizing a Waukesha Universal Series PD pump for your application, contact a Triplex Sales Engineer today.
