Grundfos NK Long-Coupled Single-Stage End-Suction Pump

Overview

The Grundfos NK is a long-coupled, non-self-priming, single-stage centrifugal volute pump with an axial inlet, radial outlet and horizontal shaft, mounted with its motor on a common steel base frame. Grundfos builds the Grundfos NK range according to ISO 5199, with connection dimensions to EN 733 and flanges to EN 1092-2, so it fits standard pump foundations and pipework and can replace other EN 733 pumps without major changes. The data booklet lists pump housings with outlet flanges from DN 32 to DN 350, ratings for 10, 16 or 25 bar operation, and liquid temperatures from -25 to +140 °C in the standard range, extending to -40 to +220 °C in custom-built versions. Speed-controlled NKE versions add a motor with built-in frequency converter.

Seven Star LLC supplies the Grundfos NK to water utilities, district cooling plants, desalination facilities, industrial plants, hotels and building services contractors in the Sultanate of Oman and across the GCC. Our Muscat team helps select the hydraulic size, impeller trim, materials and shaft seal for each duty, and we provide model selection support from Muscat.

Applications

Grundfos describes the NK as a multipurpose pump for applications demanding reliable and cost-efficient supply, and groups its uses into five fields. In HVAC, the Grundfos NK circulates water in hot water heating and chilled water systems. For industrial liquid transfer it serves cooling and air-conditioning systems, boiler-feed and condensate systems, aquafarming, industrial heating and district heating plants. For industrial pressure boosting, it supplies washing and cleaning systems, wash-down systems, vehicle washing tunnels and firefighting systems. In water supply, it handles filtration and transfer at waterworks, pressure boosting in mains, high-rise buildings, hotels and industrial buildings, and swimming bath duties. In irrigation it covers field irrigation and flooding, sprinkler and drip-feed systems.

In Oman and the GCC, these translate into chilled water and condenser water pumps for district cooling, seawater intake and brine transfer at desalination plants (with suitable materials), raw and treated water transfer at water treatment works, cooling water circulation at power and process plants, and irrigation for agriculture and landscaping projects in Muscat, Sohar, Duqm and Salalah.

Engineering Design of the Grundfos NK

The Grundfos NK uses a back pull-out design: the motor, motor stool and impeller can be removed without disturbing the pump housing or the pipes, and Grundfos notes that even the largest pumps can be serviced by one person with a crane. Pumps fitted with a spacer coupling can be serviced without moving the motor on the base frame, which saves realignment after maintenance. Larger sizes have a double volute that reduces radial loads, extending seal and bearing life and lowering life cycle costs.

The bearing bracket has two sturdy anti-friction bearings lubricated for life. It is made of cast iron EN-GJL-250 and supported by a foot of EN-GJL-250 or carbon steel. Every Grundfos NK uses one of six shaft, seal and bearing sizes, with shaft diameters at the coupling of 16, 24, 32, 42, 48 or 60 mm; because the bearings and shafts are generously sized, the pump can also be driven by a belt drive or a diesel engine if required. A thrower on the shaft keeps liquid out of the bearing bracket. The closed impeller has double-curved blades with smooth surfaces for high efficiency; impellers are statically balanced to ISO 1940-1 class 6.3 and hydraulically balanced to compensate axial thrust, and they can be trimmed to the customer’s duty point. Pump housings are made of grey cast iron EN-GJL-250 or ductile iron EN-GJS-500-7 depending on the material code, and the mechanical shaft seal has dimensions according to EN 12756.

Key Features

Main features of the Grundfos NK highlighted in the data booklet:

• Built to ISO 5199, with EN 733 connection dimensions and EN 1092-2 flanges.
• Outlet flanges from DN 32 to DN 350 and pressure ratings PN 10, PN 16 or PN 25.
• Back pull-out design for maintenance without disturbing the pipework.
• Double volute on larger pumps to prolong seal and bearing life.
• Bellows and O-ring mechanical seals to EN 12756, in EPDM or FKM, for water and coolants.
• Standard IEC/DIN motors in efficiency class IE3 or IE4, with 2-, 4- and 6-pole options at 50 Hz.
• NKE versions with permanent-magnet MGE motors in efficiency class IE5, up to 26 kW medium speed and 22 kW low speed.
• Energy-optimised hydraulics complying with Commission Regulation (EC) No 547/2012 and its minimum efficiency index.

Speed-Controlled NKE Pumps

NKE pumps are Grundfos NK pumps fitted with a motor with built-in frequency converter and application software, giving an all-in-one speed-controlled unit. With a sensor installed, the pump can run in constant pressure, proportional pressure, temperature control or constant flow modes. Grundfos lists energy savings, increased comfort, control and monitoring of pump performance and communication with the pump as the main benefits of an E-pump. Any NK pump with a standard motor can alternatively be connected to an external Grundfos CUE frequency converter.

Shaft Seals and Operating Conditions

The data booklet tabulates standard seals for the Grundfos NK, for example BBQE bellows seals for 0 to 120 °C at 16 bar, BQQE for -25 to +120 °C, and DQQE balanced O-ring seals for -20 to +140 °C at 25 bar. Pumps are pressure tested at 1.5 times their pressure stage, so PN 16 pumps are tested at 24 bar and PN 25 pumps at 37.5 bar. Standard MGE motors on NKE pumps may operate at ambient temperatures from -20 to +50 °C at full rated output, and higher ambient temperatures or altitudes call for derating, a consideration that matters in the hot summers of the Gulf region.

Technical Specifications

Summary data for the Grundfos NK from the Grundfos data booklet:

How to Order

To request a quotation for the Grundfos NK, send Seven Star LLC the liquid, temperature, required flow and head, available NPSH, pressure rating, preferred materials and whether you need fixed speed or an NKE speed-controlled unit. The Grundfos NK data booklet can be downloaded from this page. You may also compare the Grundfos NB end-suction pump, the KSB Etanorm volute casing pump and the Grundfos Hydro MPC booster set. Seven Star LLC provides model selection support from Muscat for customers in Oman and the GCC.