Key features
Half the shaft speed of the two-pole NM. Where NPSHa is marginal and the two-pole pump cavitates, the four-pole build is often the fix that doesn't need the pipework changing.
The motor's extended shaft carries the impeller directly. No coupling, no coupling guard, no baseplate to set true and no alignment to hold.
Calpeda takes the extended-shaft build to 22 kW at two poles but stops at 15 kW on the NM4. Above that, the four-pole range is the stub-shaft NMS4.
The four-pole duty bands sit higher than the two-pole ones. 60 starts an hour holds all the way to 7.5 kW, where the two-pole pump drops to 40 above 2.2 kW.
Calpeda builds the casing to EN 733 for main dimensions and performance, then adds sizes outside the standard. Check your size against the standard before assuming a like-for-like swap.
Calpeda lists the NM EI and NM4 EI from 0.37 to 37 kW with the I-MAT converter on the motor. On four-pole units the control range is 870–1,750 rpm.
About the Calpeda NM4
The Calpeda NM4 is the same pump as the NM with a four-pole motor on it. Same EN 733 casing, same close-coupled construction, same clean-water duties: water supply, heating, air conditioning, cooling and circulation plant, civil and industrial work, and irrigation. What changes is the shaft speed, and that changes more than the numbers on the curve.
Buy one for the suction side. At about 1450 rpm the impeller asks less of the suction than the same casing spinning at 2900, and suction conditions are where these pumps fail. NPSHa has to beat NPSHr at the duty point or you cavitate, pit the impeller and take the seal out behind it. Where the suction tank is too small, the suction lift too long, or the medium warm enough to be near its vapour pressure, dropping to four poles is often cheaper than rebuilding the pipework. Total suction lift is up to 7 m either way.
The trade-off is size and money. Halve the speed and a given casing gives you roughly half the flow and about a quarter of the head, so you climb the range to get back to the same duty point. An NM 32/25A makes 93.8 m at two poles on 15 kW. To reach 36 m at four poles you are on an NM4 80/31A, also 15 kW, and a far larger pump. Bigger casing, heavier unit, more floor to stand it on. If your suction is good and you want head in a small frame, the two-pole NM is the right answer and we will tell you so.
The liquid rules don't move. Calpeda rates the NM4 for clean liquids that are non-explosive and non-flammable, free of abrasives, non-aggressive to the pump materials, and carrying solids up to 0.2%. Running slower does not make it a solids pump. That 0.2% sits well below the 3–4% rule of thumb where centrifugal pumps give way to positive displacement, and it is the number that decides whether this pump belongs on your duty at all. Grit abrades the wet end. Fibre binds on the impeller. If either is in the medium, ask us for a solids-handling pump instead.
The close-coupled build is the last thing to weigh. Pump and motor are a single unit, compact and with nothing to misalign, but the motor is part of the pump: it carries an extended shaft rather than a standard frame, so a replacement comes from Calpeda. Where you want a standard motor on the front, or more than 15 kW, Calpeda builds the same four-pole hydraulics as the NMS4.
How the Calpeda NM4 works
The Calpeda NM4 is a single-stage centrifugal pump. Liquid enters axially at the suction flange, the impeller throws it outwards, and the casing discharges radially from the top. A four-pole induction motor turns it at about 1450 rpm at 50 Hz. Its extended shaft carries the impeller directly, and a carbon, ceramic and NBR mechanical seal keeps the liquid off it. Calpeda publishes the curves with tolerances to UNI EN ISO 9906:2012.
Reading the designation
Calpeda's own worked example is BNM(S)4 EI 32/16A/B. A leading B is the bronze version and no letter means cast iron. NM is the series, a following S is the stub-shaft version, and the 4 is what makes it four-pole. EI marks the I-MAT converter build. Then 32 is the delivery port diameter in millimetres, 16 the nominal impeller diameter, A the impeller size, and a trailing /B a revision. So an NM4 65/20A/B has a DN65 delivery port on the 20 impeller. That single 4 is the whole difference between this pump and the two-pole NM, and it is easy to miss on a nameplate. Matching an existing unit? Send the full designation and the serial number, both read off the nameplate.
What four poles actually buys you
Four poles buys you two things: a lower NPSH requirement, and a wider duty band. The first is the reason people specify it. A slower impeller demands less of the suction side, which is the failure mode that brings these pumps back. The second shows up in Calpeda's own duty limits, which are pegged to motor rating and sit a band higher on the four-pole range. The NM4 holds 60 starts an hour all the way to 7.5 kW and 40 up to 30 kW, where the two-pole pump drops to 40 above 2.2 kW. A float or pressure switch cycling harder than the rating will cost you the seal, and the seal is the weak point in almost any pump.
What it costs you is duty per size, and the gap is not small. Across Calpeda's own tables the four-pole build gives roughly half the flow and about a quarter of the head the same casing makes at two poles. Size off the curve, not off that ratio.
NM4 against the rest of the range
Four builds share these hydraulics, and the nameplate is the only thing that tells them apart. The NM4 is the four-pole cast iron pump with the motor bolted straight on.
| Build | Speed | Drive | Max power | Motor protection |
|---|---|---|---|---|
| NM | ≈2900 rpm | Extended motor shaft | 22 kW | IP 54 |
| NM4 | ≈1450 rpm | Extended motor shaft | 15 kW | IP 54 |
| NMS | ≈2900 rpm | Stub-shaft bracket, standard motor | 75 kW | IP 55 |
| NMS4 | ≈1450 rpm | Stub-shaft bracket, standard motor | 90 kW | IP 55 |
A leading B on any of them puts the casing and lantern bracket in bronze, and caps the working pressure at 10 bar.
Standards, efficiency and the nameplate
Main dimensions and performance follow EN 733, with additional sizes added to complete the range. Flanges are PN 10-16 to EN 1092-2. Motors are built to EN 60034-1 and EN 60034-30-1, insulation class F, IP 54, and suit converter operation; three-phase efficiency is IE2 up to 0.65 kW and IE3 from 0.75 to 55 kW. Supply is 230/400 V ±10% up to 3 kW and 400/690 V ±10% from 4 kW.
The pumps are declared under European Regulation No 547/2012, and Calpeda's index for the four-pole hydraulics gives a minimum efficiency index of MEI ≥ 0.4 against a benchmark of MEI ≥ 0.70 for the most efficient water pumps. Check that against your scheme's energy target before you commit to one. The nameplate carries the type, the minimum and maximum flow and head, rated power, supply voltage, frequency, nominal motor current, rotation speed, duty, insulation class, weight, year of manufacture and serial number, along with the ESCC classification and the MEI figure.
Duty cycle, noise and dry running
Calpeda caps starts per hour by motor rating. On the four-pole range that is 60 up to 7.5 kW and 40 up to 30 kW, with maximum sound pressure of 70 dB(A) and 80 dB(A) across the same two bands. Never run it dry, whatever the speed: the seal faces are lubricated by the liquid, and a few seconds without it is enough. Somebody shutting a valve and forgetting it is shut does the same damage as a bad design.
Variable speed, and the EI build
Calpeda offers the NM EI and NM4 EI from 0.37 to 37 kW with the I-MAT converter mounted on the motor. On four-pole units the control range is 870–1,750 rpm, and the four-pole system uses a differential pressure transducer where the two-pole one uses a single transducer. It runs in constant pressure, proportional pressure, constant flow, fixed speed or constant temperature mode, and protects against dry running, operation against a closed valve, system leakage, motor overcurrent, over- and undervoltage and current imbalance between phases. On a duty that varies, that beats throttling a fixed-speed pump on running cost.
Specifications
| Type | Close-coupled single-stage end suction centrifugal, axial suction, radial delivery on top | |
|---|---|---|
| Liquid handled | Clean liquids, non-explosive and non-flammable, free of abrasives and non-aggressive to the pump materials | solids content up to 0.2% |
| Flow rate | up to 330 m³/h | four-pole, 50 Hz |
| Total head | up to 36.6 m | four-pole, 50 Hz |
| Power rating | 0.37–15 kW | three-phase, four-pole |
| Speed | approx. 1450 rpm | 4-pole, 50 Hz |
| Maximum working pressure | up to 16 bar | 10 bar on NM4 32/16, 32/20, 40/25, 50/20, 50/25, 65/31, 100/25, 125/250 and the bronze version |
| Liquid temperature | -10°C to +90°C | |
| Ambient temperature | up to 40°C | |
| Total suction lift | up to 7 m | |
| Duty | Continuous | |
| Connections | Flanges PN 10-16 to EN 1092-2 | |
| Delivery port sizes | DN32 to DN125 | |
| Pump casing | Cast iron GJL 250 to EN 1561 for PN 10; cast iron GJS 400-15 to EN 1563 for PN 16 | |
| Lantern bracket | Cast iron GJL 200 to EN 1561 | |
| Impeller | Cast iron GJL 200 to EN 1561 | brass CW617N to EN 12167 on the 32/16 and 32/20 sizes |
| Shaft | Chrome-nickel steel 1.4305 to EN 10088 (AISI 303) | |
| Mechanical seal | Carbon / ceramic / NBR | |
| Bronze version (BNM4) | Casing and lantern bracket in bronze CC480K to EN 1982, bronze impeller, AISI 316 shaft | |
| Motor | Four-pole three-phase induction, insulation class F, IP 54, suitable for converter operation | |
| Motor efficiency | IE2 up to 0.65 kW, IE3 from 0.75 to 55 kW | EN 60034-1 and EN 60034-30-1 |
| Voltage | 3~230/400 V ±10% up to 3 kW; 3~400/690 V ±10% from 4 kW | |
| Starts per hour | 60 up to 7.5 kW, 40 up to 30 kW | four-pole bands |
| Sound pressure | 70 dB(A) up to 7.5 kW, 80 dB(A) up to 30 kW | maximum |
| Ecodesign | MEI ≥ 0.4, declared under Regulation (EU) No 547/2012 | |
| Test tolerances | UNI EN ISO 9906:2012 | |
| On request | Other voltages, AISI 316 impeller on the 32 to 80 sizes, 60 Hz, IP 55, special mechanical seal, IE4 motors, single-phase NMM to 1.8 kW, counter-flanges | |
| Special temperature builds | Cooling mixtures from 0 to -30°C, water from 90°C to 140°C, oil to 200°C and a maximum of 30 cSt | on request |
| Finish | Supplied fully painted |
Send us the flow, head, medium and site conditions, along with the NPSH available at the pump, and we will size the NM4 against your duty point or tell you the two-pole NM does it in a smaller frame. If you are replacing an existing unit, photograph the nameplate and send the model and serial number with the enquiry.
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Frequently asked
What is the difference between the Calpeda NM and the NM4?
The number of motor poles, and so the speed. The NM is two-pole and runs at about 2900 rpm; the NM4 is four-pole and runs at about 1450 rpm, on the same EN 733 casing and the same close-coupled construction. At four poles a given size gives roughly half the flow and about a quarter of the head, and the range stops at 15 kW rather than 22 kW.
Why would you specify a four-pole pump instead of a two-pole one?
Suction conditions, most of the time. A slower impeller needs less NPSH, so where NPSHa is marginal and the two-pole pump cavitates, the NM4 will often run where the NM will not, and it holds a wider duty band at 60 starts an hour to 7.5 kW against 2.2 kW. You pay for that in size, because you climb the range to reach the same duty point.
What flow and head does the Calpeda NM4 cover?
Up to 330 m³/h and up to 36.6 m at 50 Hz, on motors from 0.37 to 15 kW. No single pump does both ends of that. Calpeda publishes 60 Hz data separately.
What is the maximum motor size on a Calpeda NM4?
15 kW. Calpeda takes the extended-shaft close-coupled build to 22 kW at two poles but stops at 15 kW on the NM4. Above that, the four-pole range continues as the stub-shaft NMS4, which runs to 90 kW.
What does NM4 65/20A/B mean?
NM is the series, the 4 makes it the four-pole version, 65 is the delivery port diameter in millimetres, 20 is the nominal impeller diameter, A is the impeller size and the trailing /B is a revision. A leading B would make it the bronze BNM4, and an S after NM would make it a stub-shaft NMS4.
What liquids can a Calpeda NM4 handle?
Clean liquids that are non-explosive and non-flammable, free of abrasives and non-aggressive to the pump materials, with a solids content up to 0.2%. Liquid temperature is -10°C to +90°C on the standard build. Running at 1450 rpm does not widen that; anything abrasive or fibrous wants a different pump.
Can I get a Calpeda NM4 with a variable speed drive?
Yes. Calpeda lists the NM EI and NM4 EI from 0.37 to 37 kW with the I-MAT converter on the motor. The four-pole control range is 870–1,750 rpm, the four-pole system uses a differential pressure transducer, and it runs in constant pressure, proportional pressure, constant flow, fixed speed or constant temperature mode.
Is there a bronze version of the Calpeda NM4?
Yes, the BNM4. The pump casing and lantern bracket are bronze CC480K to EN 1982, with a bronze impeller and an AISI 316 shaft. Maximum working pressure on the bronze version is 10 bar.