Calpeda NMS Stub-Shaft End Suction Pump

The Calpeda NMS is a clean-water transfer and pressure pump built around a bracket rather than a monobloc motor. The hydraulics belong to the same family as the close-coupled NM, and Calpeda catalogues both for water supply, heating, air conditioning, cooling and circulation plant, civil and industrial duties and irrigation. What changes on the NMS is everything behind the casing.

The bracket is the reason to buy one. It carries a stub shaft and an integrated thrust bearing, and it is machined for a standard motor. On the NM 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 NMS you fit a standard frame, which also means you choose its efficiency class, its protection rating and where it comes from. Two poles takes the NMS to 75 kW where the NM stops at 22 kW.

What you give up is length, weight and a coupling to align. The NMS needs the baseplate set true and the coupling guard back on before anyone starts it. Where the duty is small and permanent, the NM does the same job with fewer parts to buy and nothing to align, and we will tell you so.

The bracket changes nothing about what the pump will handle. Calpeda rates the NMS 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%. That 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. Give us the duty before the margins went on, and the pipework it has to work against.

The Calpeda NMS is a single-stage centrifugal pump with an axial suction flange and a radial delivery flange on top of the casing. Everything that makes it an NMS 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 NMS 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 NMS needs a coupling guard and the NM does not. The bracket is cast iron GJL 200 to EN 1561, and it stays cast iron even on the bronze BNMS build.

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 a 4 marks the four-pole version, so a plain NMS is the two-pole cast iron stub-shaft pump. Then comes the delivery port diameter in millimetres, the nominal impeller diameter, the impeller size, and a revision. On the NMS, Calpeda writes the impeller diameter in full: an NMS 80/250A/A has a DN80 delivery port on the 250 impeller, where the NM equivalent would read 80/25. Send us that full string and the serial number off the nameplate when you are matching an existing unit.

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. 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 only the 75 kW pump at the top of the two-pole range gets IE4 as standard. Supply is 230/400 V ±10% up to 3 kW and 400/690 V ±10% from 4 to 75 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 two-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. The nameplate carries the type, the flow and head range, rated power, supply voltage, current, speed, duty, insulation class, weight, year of manufacture and serial number, along with the ESCC classification and the MEI figure.

Duty cycle and noise

Calpeda caps starts per hour by motor rating: 60 up to 2.2 kW, 40 up to 7.5 kW, 20 up to 30 kW and 10 up to 75 kW. Maximum sound pressure runs 70 dB(A), 80 dB(A), 85 dB(A) and 90 dB(A) across the same bands. A 75 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.