Calpeda NMS4 Stub-Shaft End Suction Pump (1450 rpm)

The Calpeda NMS4 is a clean-water transfer and pressure pump that turns at about 1450 rpm on a bracket rather than a monobloc motor. It shares its hydraulics with the close-coupled NM4, and Calpeda catalogues both for water supply, heating, air conditioning, cooling and circulation plant, civil and industrial duties and irrigation. Two things separate it from the rest of the family: the bracket, and the size of pump four poles lets you build.

Start with the power. The four-pole NMS4 runs from 0.75 to 90 kW and reaches 660 m³/h, which is the largest flow anywhere in the NM family. The close-coupled NM4 stops at 15 kW. So above 15 kW at 1450 rpm there is no choice to make, and below it the choice is about the motor rather than the duty.

The bracket is the other reason to buy one. It carries a stub shaft and an integrated thrust bearing, and it is machined for a standard motor. On the NM4 the motor has an extended shaft and is part of the pump, so a burnt-out motor is a Calpeda part rather than a trip to the local motor factor. On the NMS4 you fit a standard frame, which also means you choose its efficiency class, its protection rating and where it comes from.

What you give up is length, weight and a coupling to align. The NMS4 needs the baseplate set true and the coupling guard back on before anyone starts it, and a misaligned coupling will find the bearings and then the seal. Where the duty is small and permanent and you don't care whose motor is on the front, the NM4 does the same job with fewer parts to buy and nothing to align, and we will tell you so.

None of that changes what the pump will handle. Calpeda rates the NMS4 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 at half speed does not buy you solids tolerance. That 0.2% is well under the 3–4% rule of thumb where centrifugal pumps give way to positive displacement. Grit abrades the wet end and fibre binds on the impeller. If the medium carries either, ask us for a solids-handling pump instead.

Then size it honestly. Total suction lift is up to 7 m, and when one of these fails early the suction side is almost always where it started: NPSHa has to beat NPSHr at the duty point, or you cavitate and pit the impeller. The other half is margin stacking, where the consultant, the contractor and the installer each add a little and a 3 kW duty arrives with an 11 kW motor on it. At 90 kW that arithmetic gets expensive. Give us the duty before the margins went on, and the pipework it has to work against.

The Calpeda NMS4 is a single-stage centrifugal pump with an axial suction flange and a radial delivery flange on top of the casing. A four-pole motor drives it at about 1450 rpm at 50 Hz through a coupling, and everything that makes it an NMS4 sits between that casing and the motor. A carbon, ceramic and NBR mechanical seal keeps the liquid off the shaft, and Calpeda publishes the curves with tolerances to UNI EN ISO 9906:2012.

The bracket, the bearing and the motor

The NMS4 puts a bracket between the pump and the motor. A stub shaft runs through it to carry the impeller, and an integrated thrust bearing takes the hydraulic load in the pump end. The motor bolts to the front and drives that stub shaft through a coupling, which is why the NMS4 needs a coupling guard and the NM4 does not. The bracket is cast iron GJL 200 to EN 1561, and it stays cast iron even on the bronze BNMS4 build.

NMS4 against the rest of the range

Four builds share these hydraulics, and the nameplate is the only thing that tells them apart. The NMS4 is the four-pole pump on a bracket, and it is the only one of the four that reaches 90 kW.

A leading B on any of them puts the casing in bronze and caps the working pressure at 10 bar.

Reading the designation

Calpeda's worked example is BNM(S)4 EI 32/16A/B. A leading B is the bronze version, NM is the series, the S marks the stub-shaft build, and the 4 marks the four-pole version. Then comes the delivery port diameter in millimetres, the nominal impeller diameter, the impeller size, and a revision. On the NMS4, Calpeda writes the impeller diameter in full: an NMS4 100/315A/A has a DN100 delivery port on the 315 impeller, where the NM4 equivalent would read 100/31. Send us that full string and the serial number off the nameplate when you are matching an existing unit.

The NMS4 80/400, the size outside EN 733

The NMS4 80/400 is the one size Calpeda names as sitting outside EN 733. The standard covers main dimensions and performance, and Calpeda adds sizes to complete the range; the 80/400 is the size it calls out by name for the four-pole build. Treat it as a hydraulic selection, not a dimensional like-for-like swap for an EN 733 pump, and check the footprint against what is on the floor before you order one.

It earns its place. A DN80 delivery port on a 400 mm nominal impeller gives the highest head in the four-pole range, 61.6 m, and Calpeda builds it on four motor ratings from 18.5 to 37 kW. If you want head rather than flow at 1450 rpm, that is where the range tops out.

Standards, efficiency and the nameplate

Main dimensions and performance follow EN 733, with additional sizes added to complete the range, and flanges are PN 10-16 to EN 1092-2, PN 10 on DN 200. Motors are built to EN 60034-1 and EN 60034-30-1, insulation class F, IP 55, and suit converter operation. Three-phase efficiency runs IE2 up to 0.65 kW, IE3 from 0.75 to 55 kW and IE4 from 75 kW, so the 75 kW and 90 kW pumps at the top of the four-pole range get IE4 as standard. Supply is 230/400 V ±10% up to 3 kW and 400/690 V ±10% from 4 to 90 kW.

Efficiency on the hydraulic side is a different number, and a less flattering one. 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 it against your scheme's energy target before you commit to a 90 kW machine. 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, 40 up to 30 kW, 20 up to 75 kW and 10 up to 90 kW, with maximum sound pressure of 70, 80, 85 and 90 dB(A) across the same bands. A 90 kW unit cycling more than ten times an hour is a control problem, and it will show up as a seal first. Never run it dry either: the seal faces are lubricated by the liquid, and a short period without it is enough to take them out. Somebody shutting a valve and forgetting it is shut does the same damage as a bad design.