One of the differences between the Waukesha Universal 1 and Universal 2 series of PD pumps is the standard shaft material. The Universal 1 Series of pumps comes standard with 316 shafts while the Universal 2 series of pump comes with 17-4. “Whoa, hold on, why does the latest and greatest not use 316”, you might ask. This blog will take a look at the difference and try to explain to you why it shouldn’t make a difference- even if you spec says it should.
The Waukesha Universal 2 Sanitary Pump Has 17-4 PH Shafts
To begin, the latest and greatest in external circumferential piston pumps is the Waukesha Universal 2 series of pumps. Building on the success of the “Can-do” Universal 1 series of pumps, it is ideal for handling high purity process fluids. Waukesha Universal 2 series pumps are specified to handle everything from cell cultures to crude oil. Its robust design can be clean in places, steamed in place, fully drained, and used at greater differential pressures than other ECP pumps on the market. How does it accomplish this? One distinguishing factor are the 17-4 PH shafts. 17-4 PH steel has been chosen by Waukesha, and copied by others, because of the extended service it offers under extreme conditions. But it isn’t 316, and you’re not quite sure why that matters, but you have a piece of paper in front of you that says it does, so go on, and elaborate.
Well, 17-4 PH is a Martensitic, precipitation hardened steel that combines high strength and hardness with excellent corrosion resistance. 316L, on the other hand, is an Austenitic chrome nickel steel. 316L also offers excellent corrosion resistance and low levels of carbon which make it great for welding. 316L is a great general purpose steel. 17-4, on the other hand, is hardened through a high temperature heat treatment, giving it superior tensile strength, yield, and weight-to-strength properties than 316L.
So let’s look at the properties that matter for a positive displacement pump shaft and see which material we’d prefer. What aren’t we going to do to a pump shaft? Well, we’re certainly not going to weld anything to it. Pump shafts are machined and allow for the ultra-tight tolerances that make Waukesha PD pumps so efficient. We’re not going to mess with the shafts by welding something on to it. What else should our pump shafts have a high resistance to, other than corrosion? Well, they should be able to support the radial load of the spinning rotor and also not deflect, bend, or in the worst case scenario, snap at high differential pressures. An ideal pump shaft shouldn’t work harden and become brittle.
So what properties should any material have? Ideally, it should be hard, have a high tensile strength, and a good strength-to weight ratio. What material does this sound like to you? Well to me, it sounds like 17-4. While 316L is the general purpose, over-spec’ed, don’t think twice-default, when we look at what is going to make the best sanitary pump, it’s a pretty clear choice, 17-4 is the way to go. As mentioned previously, 17-4 PH shafts are standard on the Waukesha Universal 2 pumps and optional on the Universal 1 series. If you need any more convincing what shaft material you should use, contact a Holland Sales Engineer today.