If the machine holds the motor by both its feet and its flange, the type required is foot-and-flange: IM B35 with the large flange with clearance holes, IM B34 with the small flange with tapped holes. Which one to choose is decided by the type and size of the flange on the machine and by whether the feet actually carry load.

DRG-180L-6 15 kW 1000 rpm cast iron frame DRG three-phase motor – foot and flange motor type selection

First understand what carries the load

There are two scenarios on machines of this kind. In the first, the motor is fitted by its flange to a pump lantern or a gearbox, and the feet act as supports transferring the weight to the base. In the second, the motor is bolted to the base by its feet, and the flange is used only for a guard or dust cover. In the first case the flange dimensions are critical; in the second, the shaft height and foot holes are.

Decision checklist

  1. Are the flange holes on the machine clearance holes (bolt tightened with a nut), or are the holes in the motor flange tapped? Clearance holes point to B35, tapped holes to B34.
  2. Measure the bolt circle and the spigot diameter.
  3. If the feet are removed, can the motor hang from the flange? If so, the load is on the flange.
  4. Check that the shaft height and the flange centre are on the same axis, i.e. that the feet do not strain the connection.

The trap of double fixing

When the feet and flange are both tightened at the same time, the motor is locked at two points. If the base height does not exactly match the flange axis, the frame and flange are stressed as the bolts are tightened, which puts extra load on the bearings and pushes the centre out of line. The right way is to fix the flange first, then measure the gap between the feet and the base and fill it with shims, and tighten the foot bolts last.

When comparing options

A foot-only (B3) motor will not suit this machine; a flange-only (B5) motor may sag on heavy frames that need foot support. You can compare frame dimensions in the technical drawings and review the pump motor options; which model can be supplied in foot-and-flange form is clarified at the ordering stage.