Important Factors for Slurry Pump Motors

Slurry Pumping

The main difference between slurry and wastewater pumps is in the parts that are in direct contact with the slurry and thus subject to wear by the slurry's solid particles.

The three parts to pay close attention to are:

  • Motors
  • Shaft and Bearings
  • Seals

Motors

Important factors for slurry pump motors:

• Effective cooling
• Insulation

Effective cooling

Water cooling is superior to air cooling and gives the submerged motor a high power density and comparatively low temperature.

In the Flygt motor, developed and manufactured by Flygt, the rotor diameter is bigger and the stator thinner than in standard motors. This directs more of the losses (heat release) to the stator and to the surrounding, cooling liquid. The short heat transfer distance makes the cooling effective and keeps the working temperature low.

The pump can be cooled in three ways depending on the slurry temperature and other circumstances:

• Pumps that work fully submerged in slurry, can be cooled by the ambient liquid. The slurry temperature may not exceed 40°C.

• Pumps that work at times with the motor partially or totally un-submerged, can be equipped with a cooling jacket for internal cooling, where a cooling medium (glycol mixture) circulates (5100/5150 series).

• Pumps that often work in a low level, in hot slurry or are dry installed can be cooled using an external supply of cooling liquid, connected to the cooling jacket. This is also how to cool a partially or totally un-submerged slurry pump from the 5500 series since these pumps don't have the internal cooling option.

Cooling of the 5570 series with the big Great and Gray drive units requires a more detailed explanation. Please see the Installation Manual for details.

Insulation

Class H insulation (180°C) is applied to the stator winding by a trickle impregnation system. The Flygt pump has a motor limit to Class B (140°C), which reduces thermal stress resulting in an extended lifespan.

Trickle impregnation gives a winding fill much greater than typical dip and bake systems. This gives much higher protection against short circuits in the winding.

Shaft and bearings

Important factors for shafts and bearings:

• Shaft design and dimensioning

• Bearing type and protection

Shaft design and dimensioning

The shaft and bearings are of sturdy design. The distance between the lower bearing and the impeller is minimal, eliminating shaft deflections. This provides long seal and bearing life, low vibration and silent operation.

Bearing type and protection

All slurry pumps have two row angular contact ball bearings as the main bearing, because they give a high load capability in the radial as well as the axial direction.

The bearings are well protected with a lifetime lubrication of high performance grease.

Seals

Important factors for submersible pump seals:

• Low leakage or even zero leakage!

• Wear resistance

Leakage and wear resistance

In conjunction with leakage rate, the most important feature for seals in slurry applications is the ability to resist wear from abrasive particles.

The seals for the slurry pumps are designed to cope with highly abrasive pump media. Only the seal rings are exposed to the media. Other parts of the seal, such as springs and torque locks are protected from wear, clogging and corrosion inside the seal housing.

In addition, an isolation zone takes the pressure off the mechanical seal.

The pre-mounted Plug-in™ seal unit (5100/5150 series) is fast and easy to handle. The seal faces are closed and cannot be contaminated or damaged during service. The seal rings made of Tungsten carbide are always properly aligned to eliminate run-out.

Active Seal™ offers increased sealing reliability and zero leakage into the motor, thus a reduced risk for bearing and stator failure.

Active Seal™ features a rotating inner seal ring with laser cut pumping grooves that acts like a micro-pump, continuously preventing liquid from entering the motor.

It all adds up to:

• Reduced downtime

• Fewer required service inspections

• Fewer unscheduled maintenance checks

• Lowering your operation costs

Protection systems

Important factors for submersible pump protection:

• The possibility of detecting a leaking seal before any damage occurs

• Spin-out™ seal protection

• Overheating protection

Possibility of detecting a leaking seal

5500 series: In the area that contains cooling oil above the seal, there is a sensor that emits a warning if water enters. In addition, the oil is discolored by water leakage and this can be seen through an inspection screw on the side of the pump.

Stator housing leakage: A float switch shuts the pump down if water is detected.

5100/5150 series: The inspection chamber between the seal unit and the bearings has a built-in sensor for early detection of fluid leakage. The space can be inspected and emptied via a screw, which is easily accessible from the outside.

Spin-out™ seal protection

Flygt pumps use a patented outer seal design that protects the seal by expelling abrasive particles.

Overheat protection

Thermal sensors are embedded in the stator windings to prevent overheating.

If you have questions or need help determining the correct slurry pump for your application, contact your local Xylem representative.  

 

by Kristoffer Kratz