When choosing a new motor to replace a VOLT electric motor on a pump, three checks are decisive: the motor shaft must seat in the coupling or pump hub, the flange must match the pump casing or lantern, and the speed must be close to the pump's design speed. This article goes through these three checks in order and lists the measurements to send to DRG MOTOR.

Grey three-phase electric motor with DRG MOTOR logo; shaft, flange and speed check for a pump motor replacement

Shaft check: diameter, length and key

On coupled pumps the motor shaft drives the coupling hub; on close-coupled pumps it connects directly to the impeller. Shaft diameter (D), shaft length (E) and key width (F) must therefore be measured separately. In the VOLT V3E catalogue, for example, the 2.2 kW 2-pole V3EA 90 L2A has a 24×50 mm shaft, the 5.5 kW 2-pole V3EA 132 S2A a 38×80 mm shaft and the 15 kW 4-pole V3EA 160 L4A a 42×110 mm shaft. Even with the same shaft size, the distance from the shaft shoulder to the flange face affects the clearance on the pump side; this dimension should also be checked on the motor.

The VOLT manual recommends leaving at least 3 mm axial clearance between coupling halves and aligning carefully. Rechecking alignment with the new motor matters for the load on bearings and seals.

Flange check: B5 or B14?

For flange-mounted pump motors, the mounting is read from the nameplate or from the suffix at the end of the type code. The VOLT catalogue gives M-N-P dimensions for B5 (large flange) and B14 (small flange) in separate tables; for V3EA 90 L2A, for example, the B5 table gives M 165 / N 130 / P 200 mm and the B14 table M 115 / N 95 / P 140 mm. So the same frame can come with two different flanges. Measure the following on the existing flange:

  • M: diameter of the circle through the fixing holes
  • N: spigot (pilot) diameter
  • P: flange outer diameter
  • S: hole diameter (plain holes on B5, threaded on B14)

B5 flange dimensions in the DRG catalogue are, for example, M 165 / N 130 / P 200 mm for frame 90L, M 265 / N 230 / P 300 mm for frame 132S and M 300 / N 250 / P 350 mm for frame 160L. Your existing motor's dimensions must be compared with these one by one. The DRG range also includes B14 mounting; B14 flange dimensions are confirmed at order.

If you send photos of the flange and shaft with their measurements to DRG MOTOR, the mating dimensions can be compared to clarify which models are worth examining.

Speed check: against the pump design speed

With centrifugal pumps, flow, head and absorbed power all change with speed. The new motor's speed class should therefore match the pump's design speed, and small differences in rated speed should also be assessed for their effect on the pump curve. In DRG data, for example, the rated speed of the 2-pole 2.2 kW model is 2895 rpm, the 5.5 kW model 2930 rpm and the 4-pole 15 kW model 1465 rpm. A nameplate showing the same kW and 2 poles does not mean the shaft and flange mating with the pump are the same; all three checks must be done together.

If the pump runs on an inverter, the frequency range and the time spent at low speed should be sent as well. If the motor has failed, pump-related causes such as seal leakage, cavitation or dry running should also be investigated; otherwise the new motor faces the same conditions.

DRG options that can be evaluated

DRG Motor is a manufacturer, supplier and seller of electric motors. The three-phase motors in the DRG motor store are offered with B3, B5 and B35 mounting. Sample models that can be compared once your shaft and flange measurements have been reviewed:

  • DRG-90L-2: 2.2 kW, 2 poles, cast iron, rated 2895 rpm, shaft 24×50 mm
  • DRG-132S1-2: 5.5 kW, 2 poles, aluminium, rated 2930 rpm, shaft 38×80 mm
  • DRG-160L-4: 15 kW, 4 poles, cast iron, rated 1465 rpm, shaft 42×110 mm

For flange and overall length, see the relevant frame drawing on the DRG motor technical drawings page; for general information by pump type, see Pump Motors.

Frequently Asked Questions

My pump motor runs vertically (flange up/down). Does it matter?

Yes. In vertical mounting, bearing load and protection against water ingress are assessed differently. Mounting direction and which side the flange faces should be sent with a photo; suitability cannot be stated without it.

The flange dimensions match but the shaft length differs. What happens?

A different shaft length can change how the coupling or impeller seats. In some cases a spacer or a coupling change can be discussed, but this depends on the pump design and must be assessed by competent personnel.

The plate says B5 but the flange has threaded holes. Which is right?

Threaded holes usually point to the small flange (B14). If the plate and the flange disagree, the measured flange is what counts; send the measurements and a photo together.

Information to send to DRG MOTOR

  • Photo of the motor nameplate and, if available, the pump nameplate
  • Type code, kW, rated speed, voltage and frequency
  • Shaft diameter×length, key width, distance from shaft shoulder to flange face
  • Flange dimensions: M, N, P, number of holes and hole type (plain/threaded)
  • Mounting direction (horizontal/vertical) and foot/flange information
  • Pump type, fluid, inverter use and daily operating hours
  • Temperature and humidity in the pump room

Send your measurements and photos to DRG MOTOR via WhatsApp, the quote list, +90 (542) 666 11 11 or info@drgmotor.com, so that your pump's shaft, flange and speed data can be reviewed together to identify options that can be evaluated.

See current prices of DRG MOTOR electric motors and order online in our storeSEE PRICES →

Technical Sources

  • VOLT Elektrik Motorları — Product Technical Catalogue, Three-Phase Motors (Ürün Teknik Kataloğu, 3 Fazlı Motorlar) — REV 23.08 — IE3 aluminium frame B3 mechanical dimensions (shaft D×E, foot hole spacing) — printed page 17; IE3 aluminium frame B5 and B14 mechanical dimensions (flange M-N-P) — printed pages 18 and 20.
  • VOLT Elektrik Motor Sanayi ve Ticaret A.Ş. — Volt Electric Motors Introduction and Operating Manual (Tanıtma ve Kullanma Kılavuzu) — 2015/001 edition — Sections 7.3–7.4, Installation; Balancing and Axial Alignment (half key, belt and pulley, coupling clearance) — printed pages 7–8.