External Circumferential Piston vs. Lobe – What is the difference?
Let me start by saying, I will not write External Circumferential Piston pump the entire blog. It will be referred to as an ECP pump!
I often get asked the question, “What is the difference between a lobe pump and an ECP pump?” Let it be known that an ECP pump is NOT a Lobe pump. This is a common misconception with my customers.
Both pumps are considered to be a positive displacement pump and look similar is design. But they do differ, and the most obvious difference is in the design of the rotors. You can see in the pictures that the ECP pump has a bi-winged rotor and the Lobe pump has a rounded tri-lobe rotor. Even though this seems to be a small difference, it makes the ECP rotor hold some distinct advantages over the Lobe type rotor. I could go on for quite some time on the pros and cons of both depending on the application, but chose to spare you and only mention the three major points I feel are most important to know.
First, the ECP rotor reduces slip by a great deal. You will notice that the periphery of the ECP rotor has a much larger surface area than that of the lobe pump. This allows the Waukesha-Cherry Burrell Universal II pump to have 100% efficiency at >200 centipoise. This is largely due to the increased surface area of the rotor but is also due in part to the incredibly tight clearances (.003″-.005″). The tight clearances are made possible by the W88 non-galling metal that is used for the rotor material.
Lastly, the ECP pump handles slurry applications much better than the Lobe style pump in the event of a shut down. Typically, a slurry system will be flushed before a shut down, but there are always unexpected events in a plant. When this happens, a slurry will settle and harden around the lobes. When the pump is started up the torque required to turn the rotors through the settled slurry can cause the motor to burn up or knock the rotors out of timing. Tests show that the ECP pump rotor literally acts like a shovel and moves through the slurry with more ease and requires less torque, which does not compromise the motor. Oh, and do not let me forget to mention that knocking the timing out of whack is not a worry with the ECP pump!! Have a look at the video to get a better idea of what I am talking about.
I must be honest, before doing some research, I too, found it hard to find a difference between the two pumps. However, after talking to some manufacturers, like Waukesha-Cherry Burrell, I have found that the differences are significant and make a big impact in their performance. Hopefully, this information has shed some light on the subject!