Invented in the early 1920s by U.S. Motors (now Nidec), vertical pump motors replaced horizontal motors in agricultural irrigation applications. This helped to solve the efficiency issues and high costs of using the horizontal motors in applications they just weren’t designed for. In fact, vertical pump motors are up to 30% more efficient than horizontal motors mounted vertically in the exact same application.
In this article, we’ll uncover the differences between horizontal and vertical motors, and how these differences make vertical motors better for certain applications.
Horizontal Motors in Vertical Applications
Horizontal motors were originally used in all vertical applications as there was no other option. Even still, you ‘could’ use a horizontal motor for vertical applications, but you may not want to. A horizontal motor mounted vertically requires a stable mounting base, as any shifting or distortion will immediately or eventually lead to misalignment and vibration issues which will prematurely wear the bearings. But you’ll still often find horizontal motors mounted vertically in small pump and gearbox applications since the axial load is still low enough to not cause a lot of damage.
Vertical Flange Mounted Electric Motors
Vertical and horizontal electric motors have differences in their design, how they’re installed and operated, and recommended maintenance practices. The more you know about and understand your specific motor, the better it will operate and the longer it will last. Vertical flange-mounted electric motors are more durable and reliable in vertical applications as they are designed and manufactured to handle the high axial load found in those applications, as opposed to the radial load found in horizontal applications.
Vertical Motor Applications
Vertical motors are definite purpose motors designed for use in variable and constant torque applications, such as pumps, fans, compressors, cranes, conveyors, and other low-inertia variable-torque applications.
Vertical electric motors are connected directly to the equipment they power. As such, mounting correctly is essential. Incorrect mounting will lead to serious operational issues that will break down the motor.
Vertical motors are mounted in a vertical position on a flange base. There are two important dimensions to pay attention to when selecting the correct motor to install, they are labelled as BD and BX on the motor’s drawing.
BD refers to the motor’s precision-machined mounting base (base dimension of the motor). While BX refers to the coupling’s bore dimension. These dimensions have a very low tolerance for differences (0.001-0.0015in depending on the size of the motor) as mounting precision is essential to the life of the bearing system (due to misalignment and vibration) and, therefore, the motor itself.
The frame designation, or frame number, tells the user the frame size, dimensions, and mounting type. Frame designations are set by NEMA and are universal to all motor brands to allow for interchangeability when needed. The frame number is the frame dimension expressed between the center of the shaft and the bottom of the feet. The frame suffix letters (letters that directly follow the numbers) express variations. Below are the frame letters that denote vertical motors. You can find the frame dimensions in this document from NEMA.
- V - indicates vertical mounting only.
- P – indicates a vertical P-base motor.
- VP – vertical, solid-shaft, single- and poly-phase, direct connected, squirrel-cage induction motors for vertical and turbine pump applications with dimensions in section 18.237.
- P & PH – vertical, hollow-shaft, alternating current, squirrel cage motors for vertical turbine pump applications with dimensions in section 18.238.
- LP & LPH – vertical, solid-shaft, single- and polyphase, direct connected, squirrel-cage induction motors for use in chemical process in-line pump applications with dimensions in section 18.251. These motors have the thrust bearing in the motor.
- HP & HPH – same as LP & HPH but without the thrust bearing in the motor and with dimensions in section 18.252.
Solid-Shaft vs Hollow-Shaft
In looking through the frame suffixes above, you likely noticed that some motors have a solid shaft while others have a hollow shaft. Why the difference? The key here is the difference in how the motor is mounted to the pump. In a solid-shaft setup, the motor is attached to the pump shaft near the bottom of the motor with an externally mounted coupling. The coupling is “keyed” to allow the pump thrust to pass through to the motor shaft and for the torque to reach the pump. A solid-shaft motor is usually used in tanks and shallow pump applications.
In a hollow-shaft setup, the motor is attached to the pump shaft near the top of the motor with an integrally mounted drive coupling. Meaning the pump head shaft extends up through the hollow motor shaft and is joined to the shaft with an adjusting nut at the crest of the motor. The adjusting nut raises the pump shaft up and supports the weight and thrust on the motor shaft and bearings, and it allows a vertical adjustment of the impeller which is required for various reasons. Since the pump shaft and the motor shaft are joined together, they rotate together creating more mechanical stability between the two pieces of equipment. A hollow-shaft motor is usually used in deep-well applications.
Vertical Motor Bearing Systems
The single most critical design difference between horizontal motors and vertical motors is in the bearing system. The bearing system in a vertical motor is designed to withstand high axial loads, which are transmitted along the motor shaft in a linear direction while radial loads are perpendicular to the motor’s shaft. The design is simple with just one thrust bearing and one guide bearing. The thrust bearing is responsible for absorbing the axial load and distributing it into the mounts or stationary housing, allowing the vertical motor bearing system to withstand up to one thousand times more axial load than a horizontal motor bearing system is capable of.
Thrust load is the total measurement of the force that is directly from and directed at a turning mechanism. Thrust capacity is the calculated ability of a motor to handle its thrust load. The thrust capacity of a vertical motor must be higher than the total axial force it will be placed under, which includes the weight of the rotor, the pump’s shaft and impeller, and the total dynamic force required to lift the liquid to the surface.
You can find normal, medium, and high-thrust motors on the market:
- Normal Thrust: Horizontal motors - there is very little or no external thrust applied to the bearing system.
- Medium Thrust: In-line pump motor – the pump impellers are mounted to the motor’s shaft and the thrust bearing is located at the bottom of the motor.
- High Thrust: High thrust motors are capable of handling thrust loads above 100%, 175%, or 300% thrust capacity. The thrust bearing is located at the top of these motors.
Vertical Motor Enclosures
Since vertical electric motors are most often applied in pump applications, a totally enclosed washdown enclosure such as a Totally-Enclosed Non-Ventilated (TENV) or a Totally-Enclosed Fan-Cooled (TEFC) enclosure is the most common. But you may also find explosion-proof, Weather Protected type I, or Weather Protected type II enclosers (learn more about WPI and WPII enclosers HERE).
Can electric motors be mounted vertically? Put simply, yes. But to extend the life of your motor and for it to perform optimally, you’ll want to select a vertical motor for a vertical application.
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