Hot water circulation pumps


Hot water circulation pumps, have been developed for medium and large sized heating plants, for heating calanders, presses, large buildings and other applications which require temperatures > 140°C.

The design of these pumps is based on long years experiences in the field of handling hot water and grants high availability and reliability in operation. Discharge diameter up to 200 mm, maximum capacity 700 m³/h.


These types are single stage volute casing pumps in "back pull out" design with end suction and to centerline discharge flange. The "back pull out" design allows disassembling of the rotating pump part without removing the volute casing from the piping system. For fully utilizing the advantage of the "back pull out" design, use of spacer-type couplings is highly recommended because the driver can remain bolted to the base plate.

Volute casing

Casing with rigid support foot mounting is supplied as standard with the NHL-type. Centerline mounted design according to API 610 for temperatures > 177°C is available as an option. These pumps are for operating temperatures > 230°C will be supplied centerline mounted in any case. This avoids thermal stresses and misalignment of coupling due to heat expansion of the casing. The casing screws are of the heat resistant expansion type. For applications with temperature swings, additional cup springs are provided. Confined gaskets avoid blow-out of the liquid.

Centerline mounted design


The thrust loads of the closed impellers are hydraulically balanced by wear rings and balance holes in the impeller hub. The impellers are keyed to the pump shaft and secured by cap screws with Heli-Coil-inserts. To avoid vibrations, the impellers are dynamically balanced according to VDI-2060, grade 2,5 - 6,3.

Wear rings

Changeable wear rings are provided in the volute casing and the intermediate casing. Running clearances between the impellers and the wear rings comply with API 610.

Antifriction bearings

The pump shaft is carried in generously dimensioned antifriction bearings outside the pumped liquid. The bearings are oil-lubricated. The oil level in the bearing bracket is regulated by constant level oiler.

The standard design has angular ball bearings on the coupling side fixed on the pump shaft in axial direction by circlips. Pumps operating with frequent temperature swings are provided with bolted bearings. The bearings proved, even under severe conditions, a life time of more than 20000 operating hours.

Pump shaft

The stiff design of pump shaft allows minimum deflections and ensures cirtical speed values, remarkably higher than operating speeds at all points of the performance curve. Thus, vibration free running and high availability of the shaft sealing system is granted. Since the connections "impeller nut - impeller hub" and "impeller hub - shaft sleeve" are sealed by confined gaskets, contact of the pump shaft with pumped liquid is prevented.

Shaft Sealing

Gland packing "Kh"

Special attention was paid on the design of the gland packing. Using shaft sleeves of a high surface finish and graphite packings with a very good thermal conductivity, a rather wide range can do without any stuffing box cooling. The temperature limit for uncooled packings is approx. 200°C and depends on temperature, pressure and pump speed. Detailed information on request. Consumption of cooling water for cooled packings: 250-300 l/h. The stuffing box housing on product side is provided with a throttle bushing in front of the gland packing. The cooled version reduces the water temperature so intensively in the throttle gap that the stuffing box sees warm water only. The follower is provided with an O-ring which prevents loss of leakage packing rings and casing. A detachable gland enables an easy re-packing.

Mechanical seals

In order to meet customer`s requirements and to minimize pump maintenance, special mechanical seals for hot water pumps have been developed. With the selection of suitable face materials, and an intensive cooling of the seal casing as well as the stationary seat, utmost service life is assured. However, the water quality may have an essential influence on the service life.