Process pumps which are used in refineries and chemical plants very often have to satisfy the highest demands for sealing. The process pump series OHH was therefore extended with two hermetically sealed types, one with magnetic coupling (OHM) and the other with a canned motor (OHC). With these models, fluid transportation or delivery duties can be mastered in even the most difficult environment.
Siegfried Liegat, Dieter Lau
The OHH process pump from Sulzer Pumps is an overhung, horizontal, single-stage, radially split, centreline-mounted, mechanically sealed, heavy-duty process pump which has been designed and manufactured to fully comply with API standard 610, 9th Edition. The mechanical seals and seal support systems are totally compliant with API 682, 2nd Edition. The pump is characterised by its robust design, application versatility and long, reliable service life. A wide range of over 70 different sizes is available (see table). The OHH family has now been extended for sealless pump tasks with the OHM (magnetic coupling) and OHC (canned motor) types.
Magnetic drive
Where mechanical seals no longer provide adequate security and zero emissions are a must, the OHM type magdrive pump can be used (Fig. 1). The pump is designed and built in full compliance with the requirements of API standard 685 (sealless pumps). A magdrive coupling with strong permanent magnets ensures positive power transmission from the motor to the pump through the containment shell. Even though the system is inherently hermetically sealed, a backup secondary containment system with dry-running gas seals provides extra security. This backup system is designed to withstand full operating pressure.
Canned motor
For increasingly stringent sealing and security demands – in other words, when the secondary containment system is not allowed to have rotating seals – Sulzer offers the OHC type (Fig. 2), which is also compliant with API standard 685, 1st Edition. The OHC is a canned-motor pump, manufactured in close cooperation with Hermetic-Pumpen GmbH, Germany, a long-standing partner of Sulzer Pumps and an industry specialist in sealless centrifugal pumps. The OHC pump also efficiently handles even the most problematic and challenging pumping tasks, including:
- Toxic, corrosive and explosive fluids, such as hydrofluoric acid, acrylic acid and gasoline
- Very cold and very hot liquids (–120 °C/ –185 °F to +425 °C/+800 °F)
- Highly radioactive rated fluids
- Fluids with very low viscosity and high vapour pressure
- High-pressure circulation of liquid phases or supercritical gases
OHM and OHC in comparison
The OHM pump usually has a higher overall efficiency than the OHC. Since the motor is separate, it can be replaced without disturbing the pump. The pump can also be repaired without moving the motor. Repair work requires caution, but does not necessitate specialists.
The OHC pump excels with a motor casing that works as a safety containment without any moving seals. Moreover, it is very quiet and has no exterior rolling-contact bearings on the pump or motor. Its space requirement is smaller than the OHM because there is no need for a flexible coupling: the pump and motor are mounted on the same shaft.
Common to both types is that the net positive suction head (NPSH) is uninfluenced by waste heat from the drive. This is the case with the OHM thanks to a special circulation system (without cooling) and in the OHC owing to the optional cooled circulation system with secondary impeller.
As all three types are based on a modular system, the main hydraulic com- ponents are identical and useable across the product family. Furthermore, it is possible to rebuild one configuration into another if required to accommodate application changes.
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