Vertical hollowshaft motor

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A vertical hollow shaft motor is a definite purpose motor designed to drive deep-well vertical turbine pumps.

History

Introduced in 1922, vertical hollow shaft motors were developed to meet the specific needs of the vertical turbine pump industry. It is believed that Sterling Pump Corporation was the first pump company to work with a motor company (U.S. Electric Motors) to develop a motor and discharge casting assembly which would carry the thrust load from ball bearings at the top of the motor.[1] Motor impeller adjustments were made by inserting the proper number of “buttons” or washers between the ends of the line shaft and the motor shaft inside the shaft coupling, and then drawing the ends together. To accomplish this, all columns had to be the proper length and flanged. The new design did away with the flexible coupling and nest of bearings below the old solid shaft motors whose bearings could only carry the weight of their own rotors.

Construction

Vertical hollow shaft motors, as their name implies, employ a hollow shaft through which a pump shaft is extended. Adjustments to lift the impellers and give a running clearance for the pump casing can be made by turning a nut threaded on the shaft which is accessible at the top portion of the motor. A stretch of several hundred feet of shafting may require a lift at the top of the well, while the impeller at the bottom must be positioned within a fraction of an inch [2].

Turbine pump shafts are usually composed of many lengths joined by screw thread couplings. A power reversal may unscrew the joints of the pump shafting, causing the shafting to lengthen and buckle or break if the shafting is restrained. A non-reverse ratchet limits reverse rotation to as little as 4.5 degrees. Other versions in use today utilize pins to limit rotation. Alternatively, a self-release drive coupling on vertical hollow shaft motors lifts out of its engagement position and prevents counter rotation.

In addition to normal induction motor classifications, vertical motors are classified by thrust. Thrust is the sum of the axial forces of the weight of the pump and lineshaft and the dynamic forces of the pump to lift the liquid to the surface. Each manufacturer defines thrust ratings for their individual product rating. Common ratings are 100 percent high thrust, 175 percent high thrust, and 300 percent high thrust.

Normal thrust motors, usually a footless horizontal motor with a “P” flange, are used in general applications where there is very low or no external thrust applied to the motor bearing.

In-line thrust, sometimes called medium thrust, is a definite purpose motor. The pump impellers are mounted directly on the motor shaft. Since the pump impeller performance depends on close tolerance with the pump housing, the motor shaft and flange round-out tolerances must also be tighter than normal. The thrust bearing is usually located at the bottom rather than the top, as in high-thrust construction. This keeps the motor rotor’s thermal growth from affecting the impeller clearances.

Maintenance

Regular, routine maintenance and cleaning is the best assurance of trouble-free, long-life motor operation, preventing costly shutdown and repairs. A maintenance record should be kept. Repairs and lubrication data should be documented. The motor should be spun once a month to keep a film of oil on the bearings.

See also

References

  1. ↑ Lundy, E: "A History of the Vertical Turbine Pump Industry," page 19. 1968
  2. ↑ www.usmotors.com

External links

  • [1] A History of the Vertical Turbine Pump Industry
  • [2]
  • [3]


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