What is a JM Frame Motor? Why is it Better for Sanitary Centrifugal Pump Applications?

November 21, 2013
Centrifugal Pump Motor

Stainless Steel JM Frame Motor. Note the Drilled and Tapped Hole on the End of the Shaft

We sell a lot of sanitary centrifugal pumps and have been doing so for over 60 years.  Almost 15 years ago we started a business relationship with Waukesha and started selling their products.  One of these products, the 200 Series Sanitary Centrifugal Pump was new to us and had a very unique feature.  Instead of the industry standard NEMA C Face motor, the Waukesha 200 series used JM frame motors.  What is a JM frame motor you ask?  We asked the same thing as we were not familiar with them.

JM motors were designed specifically for rotating equipment with rotating seals, in other words, pumps. Specifically, pumps with mechanical seals (the benefits and applications of which we’ve discussed in previous posts).  They are different from standard C Face Motors in that they have thicker shafts and more robust bearings.  The shaft on the JM frame motor is drilled and tapped to allow the impeller to be attached from to the front of the shaft.   They do use the standard NEMA C Face dimensions for the mounting bolt pattern on the face of the motor.

After supplying hundreds of JM frame motors on sanitary centrifugal pumps, we can without hesitation say that we prefer them to C face motors.  Why?

  1.  Who wouldn’t want a sanitary pump with heavier bearings to power a piece of critical process equipment?
  2. It is easier to install a sanitary centrifugal pump assembly onto a JM frame motor than a C face motor.  We assemble sanitary centrifugal motor/pump assemblies every day.  Trust us. Installing a sanitary pump onto a C Face motor normally entails sliding a stub shaft over the motor.  You then need to properly locate the stub shaft and lock it in place using some type of clamping mechanism.  This usually entails multiple measurements and often requires a lot of trial and error.  Once the shaft is properly located (it can take several tries) you have to assemble the seals, back plate and the impeller. You better have a friend to help you. Also, try doing this under a tank with a ½” of water on the ground lying on your back.  You will love it.  To install a JM frame sanitary centrifugal pump assembly, you can pre-assemble most of the pump including the seals and simply slip it onto a keyed motor shaft.  A single bolt goes through the front of the impeller to the motor shaft holding the entire assembly together. After measuring the impeller clearances, the assembly may have to be removed and a shim put in place.  But that is a lot easier that trying to re-adjust a stub shaft on a C face motor.
  3. Sanitary Centrifugal pumps with JM frames are easier to service.  Servicing a sanitary centrifugal pump normally entails changing the seals.  To service the Waukesha 200 series sanitary pump you simply pull the front casing off, unscrew the impeller bolt and you can pull the entire pump assembly off.  The seals can be replaced working at a bench.  Most sanitary centrifugal pumps with C face motors come apart in pieces and have to be re-assembled in pieces in place.  Again go back to the being under the tank in a ½” of water analogy.  Which would you prefer?
Centrifugal Pumps

Waukesha S200 Centrifugal Pumps with TEFC JM Frame Motors

What is the down side of the JM frame motor?  Not much.  The biggest issue is availability.  Because the JM frame motor is not as common as C face motors they may have longer lead times.  But we have really not had many problems getting them.

So if you are buying a sanitary centrifugal pump should you use the model with the JM frame motor or the one with the C face motor?  Either will work, we sell both types, but prefer the JM style.  Here is one way of thinking about it; Wouldn’t you want your sanitary centrifugal pump, that is in a critical application to be coupled to a motor specifically designed for pumps over a more generic model designed to fit all sorts applications?  We would.

As always, if you have any questions about this topic or if we can be of any help to you, contact us via our web page or call at 800-800-8464