Twin Screw Pumps- What Are they and When Should You Use Them?

While many know SPXFlow/Waukesha Cherry Burrell for their industry leading line of external circumferential piston (ECP) Universal series pumps, did you know they also have another category leader with their Universal Twin Screw or UTS pump? In today’s post, we’re going to do an overview of Twin Screw pump technology and talk about a few applications we love them in and also some reasons you may want to stick with your existing ECP.

Twin Screw Pumps- What are they?

First, let’s talk a little bit about Twin Screw pumps specifically for sanitary applications. About 10 years ago, Twin Screw pumps burst onto the scene in a big way in the sanitary space. Twin screw pumps, like traditional ECP or lobe pumps, are positive displacement type pumps. They give you a constant flow per revolution regardless of discharge pressure.

Tight sealing cavities create excellent suction

Twin screw pumps, as the name would imply, use a set of meshed screws to create sets of sealed cavities that moves the fluid being pumped along an axial path. The sealed cavities create a positive pressure that moves fluid from the pump inlet to the outlet in a smooth, consistent manner.

This creates gentle product handling and the ability to pump shear sensitive fluids with larger particulates in lower pressure applications. The axial flow path also allows us to handle higher discharge pressures than we typically can with an ECP pump.

Screw pitch options for Waukesha UTS

Waukesha UTS screws are available in 3 different profiles including wide, medium, and narrow pitches to provide a wide range of pressure and flow capacities depending on application and product size. Wider pitch screws are used for lower pressure, higher flow applications, while narrow pitch rotors leverage their larger helical surface for high pressure, lower flow rate applications of where we need maximum suction at the pump inlet.

When should you use a Twin Screw Pump?

As we alluded to above,  there are three applications we absolutely love to use the UTS in.

Because of the range of screw pitches available, pumping fluids with large solids is a great twin screw application. The wide pitches allow for whole solids handling that greatly reduces the damage we see in comparable products when running an ECP pump (even with single wing rotors). Think about applications like Greek Yogurts with whole fruits and apple pie filling.

We also love twin screw pumps for high pressure, low suction applications. We once supplied a customer who had been using a competitors ECP pump on his evaporator with a UTS and it was one of the few times anyone has ever thanked us for selling them a $30,000 pump assembly. Twin screw pumps are great for low suction applications like evaporators because of the sealed cavities the screws create. And the axial flow path (as opposed to the overhung radial motion of a ECP rotor on a shaft) also allows us to handle pressures up to 375 PSI!

Finally, and probably the best application, for a twin screw pump is dual-duty applications where we need to run both product and CIP. Because of the axial flow direction we talked about above, we’re able to run twin screw pumps at much higher speeds than we can run an ECP pump. While we can typically run ECPs up to about 500 RPM, with a twin screw, we can go all the way to 3500 RPM! This allows us to create the large amounts of turndown needed to run product at slower product flow rates and also create the 5-7 fps needed for turbulent flow during CIP, eliminating auxiliary CIP pumps and valving, greatly simplifying installation.

When shouldn’t you use a Twin Screw Pump?

So why not use a twin screw? About 10 years ago when twin screw pumps burst onto the sanitary pump scene, there were a few folks who only sold twin screws and did a really good job of making every application a twin screw application. Pumping Greek Yogurt? Twin screw. Mayonnaise? Twin Screw. Beer? Twin Screw. A product you’ve been handling for 20 years with an ECP pump without issue? Twin screw. You get the idea- every application between a twin screw pump application.

The reality is, twin screw pump technology, while robust and versatile, isn’t for every application. They cannot be piped inline and twin screw pumps have a large footprint. When used in high turndown applications, twin screw pumps require exceptionally large motors.

Twin screw pumps are also much more complex to service and there is less familiarity with twin screw technology among maintenance personnel than with other, more established technologies. Screws must be properly matched and timed, often requiring special training of maintenance teams. Accordingly, we don’t recommend twin screw for clean out of place applications.

Cost is also a key consideration, with twin screws costing up to 50% more than comparably sized ECP type pumps. This carries through to parts, which has a great impact on total cost of ownership. As we mentioned above, one of the reasons we love twin screw technology is it allows us to do two duties- process and CIP- with one pump. Not only does it make piping easier, it also helps make the economics work.

To close out this post, the key takeaway is that twin screw pumps are a robust positive displacement pumping technology with many benefits that make them ideal for today’s process environments. They can handle high pressures and are gentle on large solids. They can also eliminate the need for auxiliary CIP pumps and valving for use in clean in place applications. But they are not the end all be all. Twin screw pumps are expensive compared to ECP pumps and are more difficult to service. If your current ECP pump isn’t broke, a twin screw isn’t going to fix anything. And as always, if you have any questions about which pump is best for your application, contact a Triplex Sales Engineer today!

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