If you asked everyone at Triplex what our “One Thing” is, I think we’d all give you the same answer- Waukesha PD pumps. At the core of every Waukesha ECP pump is the ECP or external circumferential piston, more commonly known as the rotor. In today’s post, we’re going to take a look at the different clearance options Waukesha offers on their ECP line of Universal Pumps, what they are, and when you should consider them.
Standard Clearance/Low Viscosity & Wine Clearance Rotors
This clearance, known as standard clearance on Universal 1 and Universal 2 pumps and low viscosity on Universal 3 pumps are for applications with temperatures up to 180 F (82 C). There is some gray area here though, and if we’re operating between 160-200 F, we’ll want to consider other factors like pump speed, differential pressure, lubricating properties of the fluid, and product viscosity. If these factors trend toward a difficult application (high speed, high pressure, non-lubricating), then we may want to consider a Front Face or Hot clearance.
The standard or low viscosity rotors are great for thin fluids where we don’t have to worry about thermal expansion of the rotors.
So why isn’t this the standard rotor in the U3, you may ask? Well, the reality that when we’re pumping any fluid over about 200 cps, which is the vast majority of Universal Pump applications, both standard clearance and hot clearance rotors will give you almost 100% volumetric efficiency, while the hot clearance is a little more forgiving.
Another clearance you’ll hear about with close to the same specs as standard clearance is “wine clearance”. Wine clearance rotors provide additional clearance between the rotor hub and the cover bore area, providing extra protection against rotor contact in this area.
Front Face (FF) Clearance Rotors
Front face clearances provide additional clearance in the front face area only. Front face clearance is recommended for thin fluids between 180 F and 200 F, giving us better pumping efficiency (less slip) than hot clearance rotors in these applications.
Hot Clearance Rotors/U3 Standard Clearance
Hot clearance rotors or the U3 standard clearance rotor are used in applications anywhere from -40 F all the way to 300 F. Hot clearance rotors provide additional clearance in the front face, as well as the rotor to body areas. Because there is more clearance, on thin fluids we’ll see more slip and will need to run the pump faster to overcome this. As mentioned above, this isn’t really an issue with fluids of a viscosity over 200 CPS, which are about 95% of applications. That’s one reason why they’re the “standard” Universal 3 rotor clearance.
One other thing to note- because there is more clearance, our horsepower requirements are generally less with hot clearance rotors than with a standard clearance rotor.
316SS Clearance Rotors
This clearance is for rotors made from 316L. Standard rotors are made from Waukesha Alloy 88, which is a high nickel, non-galling alloy. Because the Alloy 88 rotor is softer than the 316L body, it’s OK if they rub a little. This isn’t the case with a 316L rotor. With a 316L rotor and a 316L body, we risk galling if the rotor and body make contact. Accordingly, 316L clearances are even larger than hot clearance rotors, ensuring there is no contact. As with Hot clearance rotors, with lower viscosity fluids, we’ll need to run 316SS clearance rotors faster on thin fluids to overcome slip.
So what happens when we’re running a 316 rotor at temperatures over 200 F? Hopefully you’ve picked it up by now- we use 316SS hot clearance rotors which have even wider clearances to allow for thermal expansion.
Extra Hot Clearance Rotors
Extra Hot clearance rotors are a little bit of a misnomer. Sometimes called “Chocolate Rotors”, we use extra hot clearance rotors not just on higher temperature applications, but rather when we have products like chocolate that tend to plate or coat. Because we can see such a decrease in volumetric efficiency when applied incorrectly, we advise that you only use Extra Hot clearance Rotors in consultation with Triplex Sales Engineers.
Single Wing Rotors
Our last rotor type doesn’t focus as much on clearance as it does overall geometry. Instead of the two wings, a single wing rotor, as the name implies, only has a single wing. We use single wing rotors when we want to create extra large cavities to convey product. This is ideal for pumping whole fruits where we want to minimize damage to the product and maximize product integrity. While the volumetric displacement is identical, we need to be careful with speed on single wing rotor applications. Due to the geometry, we don’t want to run these over about 300 RPM.
That’s a wrap on most of the available Waukesha Universal Pump clearances. The big takeaways here are temperature, material, and product. Consider all of these when selecting your rotors and rotor clearances. They are the key to maximizing volumetric efficiency and reducing the risk of a rotor contacting the pump body. As always, if you have any questions about your sanitary PD pump application, please contact a Triplex Sales Engineer today.