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The Different Ratings and Enclosures for Sanitary Pump Motors. What do they Mean?

January 8, 2014

Most of the sanitary pumps we supply go out the door with an electric motor attached to them.  When choosing an electric motor to run a sanitary pump the buyer is presented with a variety of options.  This is a very broad topic.   In this post we will attempt to cover the main options and try and bring some clarity that might help you decide what is the best motor for your application.

Standard or Premium Efficiency

Most motors we use are offered in either standard efficiency or premium efficiency models.  In our opinion, the minimal cost of moving up to a premium efficiency motor is money well spent for several reasons. First, let’s take a brief look at motor efficiency. The efficiency of an electric motor is defined as the ratio of usable shaft power to electric input power.  The shaft power is transferred to the machine driven and the electric input power is what is metered and what you have to pay for.  Loss in motor efficiency is determined by the difference between the input power and output or shaft power.  Motor energy loss in mainly heat caused by many factors, including loss from the coil winding, loss in the rotor bars and slip rings, loss due to magnetizing of the iron core, and loss from friction of bearings.

Considerable variation exists between the performance of standard and energy- efficient motors.  Premium efficiency motors feature improved design, materials and insulations that enable them to accomplish more work per unit of electricity consumed.

Premium efficiency motors also offer additional benefits.  Because they are constructed with improved manufacturing techniques and superior materials, they usually have higher service factors, longer insulation and bearing lives, lower waste-heat output, and less vibration of which increase reliability.  Most motor manufacturers also offer longer warranties for their most efficient models.

Sanitary Centrifugal Pumps with TEFC  Finned Motors

Sanitary Centrifugal Pumps with TEFC Finned Motors

Enclosures:  TEFC or Washdown

Motors come in a wide variety of enclosures, but we will limit the discussion to two, TEFC and Washdown.  TEFC stands for totally enclosed fan cooled.  These motors usually come in two variations, smooth rolled steel enclosures or cast iron with fins.  Larger horsepower TEFC motors are usually cast with fins to optimize cooling.  TEFC motors offer better protection from moisture than open wound motors.

Washdown motors are designed for harsher environments such as food plants.  They have better sealing to protect motor internals.  The shafts have better seals and are often made from stainless steel.  Washdown motors also have smooth externals allowing for easier cleaning and fewer entrapment areas.

Waukesha PD Pumps with Washdown Motors

Waukesha PD Pumps with Washdown Motors

VFD Rated Motors

Most variable frequency inverters today are of the fast-switching, pulse-width-modulated (PMW) design.  Used on a standard motor these VFDs can lead to voltage overshoots.  These voltage spikes can cause premature failure in standard motors.  As a rule of thumb, most high efficiency motors can be operated with VFDs in applications with up to a 10:1 turndown.  For turndowns beyond that, a VDF rated motor is advised.

VFD motors are wound with voltage spike resistant insulation.  These insulation systems greatly reduce decrease the wear on motors that are subjected to transient voltage spikes.  VFD motors also provide wider constant torque over their entire speed range.  This is not the case with standard motors.  This can be a big issue in sanitary PD pump applications.

Stainless Steel Washdown, Inverter Duty Motor Mounted to a Sanitary Centrifugal Pump

Stainless Steel Washdown, Inverter Duty Motor Mounted to a Sanitary Centrifugal Pump

Explosion Proof Motors

Often explosion proof motors are required in hazardous sanitary environments, such as when pump solvents.  Explosion proofmotors are electric motors designed to both contain an explosion if it occurs within the motor and prevent the release of explosive gases or vapors to the surrounding environment.  Explosion proof motors are built to the requirements of both UL and NEC.  They are characterized by Class, Group and Temperature Code restrictions.  We won’t go into the different classes and groups in this post.  These requirement are usually already defined by the manufacturing environment the pump is going into.

Hopefully this posts will bring you more knowledge regarding choosing the best motor for your sanitary pump application.  We put sanitary pumps into 100’s of applications a year.  If you have any questions on this topic or we can be of further service to you, contact us via our web site or call at 800-800-8464.

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