For grease- and oil-lubricated bearings, the amount of lubricant is critical. Overheating and leakage are possible when too much or too little is used to fill the reservoir on the job site. To avoid spillage, manufacturers ship vertical oil-lubricated motors without oil in the oil reservoir. Follow the motor manufacturer’s instructions carefully when filling these reservoirs. There is a difference between the amount of oil shown on the oil site gauge when the motor is running and when it is stopped. Manufacturers generally indicate the proper oil level for when the motor is at a standstill. While both horizontal and vertical oil-lubricated motors may have separate cooling reservoirs, horizontal motors—especially on large compressor applications—may share the lubrication system with the driven equipment. Vertical motors with spherical roller bearings are not designed to run without an adequate amount of down thrust to preload the bearing and keep the rollers from skidding.
If the motor runs disconnected from the pump, the rollers may skid and damage the bearing. Check with the manufacturer for instructions before running the motor uncoupled for an extended period of time.
6. Balancing & Vibration
Vertical motors can experience greater vibration than horizontal motors. That is because horizontal, foot-mounted motors are bolted to a solid base. With vertical motors, only the lower end is attached to a mounting flange, while the upper end remains unsupported. Most vertical motor vibration problems involve system resonance. Because system reed critical frequency (RCF), a function of motor and base fitness, can be difficult and costly to correct in the field, steps should be taken during design and equipment procurement to ensure that RCF is not within the application’s operating speed range. While the motor usually exhibits high vibration, an RCF issue is likely to be an issue of system resonance rather than motor rotational balance. In this case, the “system” includes the motor, pump head and foundation. Proper pump installation is just as important as mounting the motor to the pump head. Noise level differences are not necessarily related to mounting position. Vertical motors sometimes reflect sound reflection from overhead structures or ceilings; horizontal motors typically do not.
The Tip of the Iceberg
These are just a few of the differences between vertical and horizontal motors. There are also differences in the ways motor performance is tested under load—and what to expect in the results. Thrust bearing requirements, belted applications, soft foot conditions, and more can also impact performance and should be considered when specifying, designing, installing, operating and maintaining electric motors. All are key to a long, productive life.