DICKOW® hot water circulation pumps, type NHL, HPL, HPR and NHM, have been developed for medium and large size heating plants, for heating calendars, presses, large buildings and similar applications which require temperatures > 140 ºC (284 ºF). The design of the pumps is based on long years of experience in the field of handling hot water and grants high availability and reliability in operation. The NHL series is designed for pressures up to 45 bar @ 238 ºC (464 ºF), maximum capacity is approximate 900 m³/h (3960 gpm) and differential head approximate 150 mLC (492 ft). The HPL/HPR series is designed for pressures up to 80 bar @ 280 ºC (536 ºF), maximum capacity is approximate 300 m³/h (1320 gpm) and differential head approximate 60 mLC (197 ft).
N/AImpellers are casted in one piece with solid hubs. To minimize thrust loads, 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. The impellers are properly statically and dynamically balanced acc. to DIN ISO 1940T1 Grade 6.3.
N/ADue to high vapor pressures of hot water, standard mechanical seals cannot be used for high temperatures.
N/ADesign The pumps are single stage volute casing pumps in "back-pull-out" design with end suction and top centerline discharge flange. The "back-pull-out" design allows disassembly of the rotating pump parts 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 then remain bolted to the base plate.
Volute Casing Casings with rigid foot mounting are supplied as a standard for the NHL/NHM type. The casing bolts are of heat resistant expansion type. For applications with temperature swing, additional cup springs avoid leakage, caused by thermal expansion. Confined gaskets avoid blow-out of the liquid. Centerline mounted design according to API 610/ISO 5199 is available for high operating temperatures on request. This minimizes thermal stress and misalignment of the coupling due to heat expansion of the casing during operation. All of the HPL/HPR-pumps will generally be provided with centerline mounted casings.
Wear rings Volute casing and intermediate casing are both fitted with renewable wear rings held in place by a press fit with locking screws. Additional impeller wear rings available as an option. The running clearances are in accordance with API 610.
Shaft, shaft sleeve The pump shaft is able to transmit the full driver output and is accurately machined throughout his entire length and is properly finished at the bearing surfaces.
In order to have satisfactory seal performance the shaft diameter and overhung are sized to minimize shaft deflection at the seal faces.
The shaft design guarantees a critical speed of more than 10% over the maximum operating speed. The connections "cap screw - hub" and "hub - shaft sleeve" are sealed by confined gaskets and the pump shaft has no contact to the pump fluid.
Antifriction bearings The pump shaft is carried by generously dimensioned antifriction bearings outside the pumped liquid. The bearings are oil-lubricated. The oil level in the bearing bracket is regulated by a constant level oiler.
The standard design has angular ball bearings on the coupling side fixed on the pump shaft in axial direction by circlips. The HPL-pumps and NHL-pumps in temperature swing applications are provided with shaft nuts.
The roller bearings takes the remaining hydraulic radial loads. The bearings proved a life time of more than 25000 operating hours even under severe conditions.
If required, bearing bracket cooling is available, on request.