Shaft-Down Vertical Electric Motors: Choosing V1 or V5, Axial Load and Sealing

A municipal pumping station lost the motor on its vertical pump. With the station down, someone took a horizontal flanged motor off the shelf, stood it shaft-down on the pump and had water flowing again the same afternoon. Six months later the lower bearing started to growl. When the motor came off, there was rust around the shaft exit and water droplets in the grease. Power, speed and flange were all correct. Nobody had asked which way up the motor would run.

A shaft-down motor looks like a horizontal one turned through ninety degrees, but the load path, the route water takes and the job the bearings do all change. This article walks through those differences using situations we see in the field, and ends with what an order for such a motor actually needs to say.

V1 versus V5: same shaft direction, different support

IEC 60034-7 defines mounting arrangements with IM codes. Two of them cover shaft-down operation:

• V1 (IM 3011): a large-flange (B5) motor standing vertically with the shaft pointing down. The motor sits on the pump casing or on a lantern (adapter) and its whole weight goes through the flange bolts. Most vertical centrifugal pumps, inline pumps and top-entry mixers use this layout.
• V5 (IM 1011): a foot-mounted (B3) motor turned shaft-down. The feet are bolted to a wall or a vertical bracket. You find it on belt-driven vertical machines and small bracket-hung drives.

The difference is more than where the bolts go. In V1 the flange carries the frame and there are no feet. In V5 the feet, designed to stand on a floor, end up holding a hanging mass against a side face. On larger frames that loads the foot bolts in shear, which is why designers usually switch to a flanged arrangement beyond a certain size. The shaft-up counterparts V3 and V6 are covered in our article on shaft-up and wall mounting, and the footless small-flange V18 arrangement in the IM V18/V19 guide.

What gravity does to the bearings

In a horizontal motor the rotor weight presses on the bearings from the side, as a radial load. Stand the motor up and the same weight pulls along the shaft axis, so it becomes an axial load on the locating bearing. On small frames this rarely matters. As rotor mass and speed go up, the bearing arrangement's axial capacity starts to decide the design.

The pump is the more delicate part. A centrifugal impeller produces its own axial thrust while running. Some vertical pumps have their own thrust bearing to absorb it; on others the impeller is mounted straight on the motor shaft and the motor bearings take the thrust. In that second case, compare the pump's figure with the permissible axial force in the motor catalogue, which is given separately for each mounting position and load direction. If the pump data sheet lists an axial load to be carried by the motor, that number belongs in the motor order. Vibration behaves differently too. A vertical motor is only as steady as the lantern or bracket it sits on. A thin sheet-metal bracket can make a well-balanced rotor look rough.

How water finds its way in

Shaft-down mounting creates two weak points. The first is the fan cowl, now at the top with its air intake facing the sky; the measures for outdoor sites are described in our rain canopy article. The second is the shaft exit at the bottom. Rain, washdown water or leakage from the pump gland runs down the outside of the frame and collects around the shaft. A seal that stays wet all the time wears at the lip, and eventually water migrates into the bearing housing.

So on shaft-down motors the seal type, an extra slinger such as a V-ring where needed, and routing any gland leakage to the floor rather than onto the motor are planned together. Condensation also counts: in a pump room that cools at night and warms by day, water can collect inside the frame. Drain holes have to sit at the lowest point for the actual mounting position, and on a horizontal motor that has been turned they end up in the wrong place. On HEM Motor three-phase series an anti-condensation heater can be requested at the ordering stage; protection is IP55 as standard, with IP56 and IP65 as options.

Fitting onto the pump: flange, spigot and shaft end

For a V1 motor to seat on the pump, the flange outside diameter, bolt circle, spigot diameter and number of holes all have to match. These depend on flange size, and one frame can be offered with more than one flange, so "B5 flange" alone is not enough; state the flange size as well. Shaft diameter, shaft length and key must suit the coupling or the directly mounted impeller. Coupling gap and alignment are harder to see on a vertical set than on a horizontal one; choosing the coupling type is covered in our flexible versus rigid coupling guide.

Power and speed selection doesn't depend on mounting. Getting from flow and head to motor power is explained step by step in the pump motor selection guide. On a 50 Hz supply, vertical pumps most often use 2-pole (about 3000 rpm) or 4-pole (about 1500 rpm) motors.

Decisions that cause trouble on site

Turning a horizontal motor on end, as in the opening example, is the most common. It runs fine at first and the problems appear months later at the bearings, seal and drains. Another is building a V5 bracket instead of a V1 lantern because it is easier to fabricate; on large frames the foot joint adds vibration. A third is ordering "the same as the old one" when the old nameplate shows no mounting code, without saying how it was installed. If the code isn't on the plate, send a photo of the motor in place and describe the shaft direction and fixing.

An order for a shaft-down motor should state:

• The IM code or a plain description: V1 (flanged, shaft down) or V5 (foot-mounted, shaft down)
• Flange size, shaft diameter and shaft length
• Axial load passed from the pump to the motor, and whether the pump has its own thrust bearing
• Installation: enclosed pump room or outdoors, with or without washdown or leakage
• Power, speed, voltage and required protection class, plus anti-condensation heater and winding temperature sensors if needed

Summing up

Choosing a shaft-down motor means accounting for load direction and water paths as well as power and speed. When the V1/V5 support difference, the pump's axial thrust and sealing at the shaft exit are settled up front, the motor avoids the problems a turned horizontal motor develops within months. HEM Motor three-phase series can be ordered in vertical positions V1, V3, V5, V6 and V15 depending on frame size. You can see the options on the mounting types page and send your pump data to our technical team.

Frequently Asked Questions

Can a horizontal flanged motor run vertically with the shaft down?

On small frames and for a short period it may run, but if the bearing arrangement, seal and drain holes were set up for horizontal use, water ingress and bearing trouble tend to follow. For a permanent installation it is safer to order the motor as V1 from the start.

What is the difference between V1 and V18?

Both are footless, flanged, shaft-down arrangements. V1 is the vertical form of a large-flange (B5) motor and V18 the vertical form of a small face-flange (B14) motor; the flange dimensions and bolting differ, so one cannot replace the other.

Does the motor carry the pump's axial thrust?

That depends on the pump design. Pumps with their own thrust bearing take it themselves, while pumps whose impeller sits directly on the motor shaft pass it to the motor bearings, and the figure then has to be checked against the permissible axial force in the motor catalogue.

Is IP55 enough for a shaft-down motor?

In a closed, dry pump room it usually is. Outdoors, under washdown or where the pump gland leaks, consider IP56 or IP65 together with extra sealing at the shaft exit and a rain canopy over the fan cowl.