Applications
Magnetic driven HZSM/HZSMA pumps are designed improve plant and personnel safety especially when handling toxic, explosive or other dangerous liquids which react on contact with the atmosphere. For all these services the containment shell replaces double acting mechanical seals with external fluid reservoirs and the necessary control equipment. HZSM/HZSMA pumps therefore offer exceptional benefits to the chemical, petrochemical and allied industries and fulfill all environment protection rules.
Due to the fact that 90% of pump failures are caused by leaking shaft seals, the sealless design increases the availability and reduces maintenance costs.
The HZSM type is used in tank farms, for offloading rail cars and trucks, filling of storage tanks and other applications where priming of empty suction pipes is required. Considering low NPSH values, gas handling capability and sealless design, the HZSMA type offer special benefits to liquified gas applications. Typical applications is filling of LPG trucks and rail cars in refineries.
Construction
The HZSM / HZSMA pumps are single or multistage horizontal centrifugal pumps, combined with integrated side channel stage on discharge side, and permanent magnetic coupling. The containment shell forms a closed wetted end and separates the pumped liquid from the atmosphere.
Design Features
Containment Shell
The containment shell is designed as a pressure vessel to separate the pumped liquid from the atmosphere only. The shell is not used used as an additional bearing holder. Therefore no dynamic stress occurs. The shell is sealed against the atmosphere by a confined gasket.
Magnetic Coupling
The single elements of the multipolar magnetic coupling are manufactured of a permanent magnet material 'Cobalt Samarium Rare Earth' with unlimited lifetime. The magnets in the internal rotor are completely encapsulated, no contact with liquid occurs.
Energy is transmitted to the hermetically sealed liquid end by a bank of external magnets passing motive force through the containment shell to a bank of internal magnets. Inner and outer magnet rings are locked together by magnetic power and are working as a synchronous coupling. The inner magnet ring transmits the required torque direct to the impeller.
Overload of the magnetic coupling and slipping will not effect demagnetization. The magnet drives are designed for electric motors, direct on line starting. Should a subsequent increase of motor power be required, ie. when installing a larger impeller, the nominal power of coupling can be increased accordingly by an additional series of magnets. The maximum drive power is approximately 150 kw at 2900 min-1
Sleeve Bearings
The internal bearings are of the sleeve type, positioned in the pumpage. Standard material is diamond coated pure Silicon Carbide, highly resistant against corrosion and wear and providing also dry running capability. Internal circulation, pressurized magnet end.
When pump is in operation, it generates eddy currents which heat up the containment shell and the pumpage in the magnet area. This heat is dissipated by internal product circulation. The internal circulation flows from discharge through the magnet area back to the inlet of the last impeller.
The capacity of the cooling flow, together with pressurization of the magnet end, prevents vaporisation or flashing of pumpage in this area when handling boiling liquids.
Balanced Thrust Loads
The thrust loads of the closed impellers are hydraulically balanced in a way that forces of the impellers are acting in the containment shell direction. These forces will be balanced by the balancing disk.
The front side of the balancing disk is pressurized from the discharge side with the pressure, the rear side is connected with the first pump stage and thus, pressurized with the lower pressure. The difference between the constant pressure and the variable pressure creates a counter force in direction to the suction flange. The value of this reaction force depends on the pressure respectively the variable gap. That means the balancing disk floats until the forces at impeller and disk are balanced. During operation is no contact between the rotating SiC ring in the disk and the stationary SiC ring in the casing.
Suction and Discharge Casing
The pump flanges of HZSM pumps are provided principally in vertical top position to grant a certain quantity of liquid in the pump which is necessary for priming empty suction pipes and lifting pumping liquid from underground storage facilities. For obtaining low NPSH value, the suction casing is designed in volute shape.
The HZSMA pumps - for applications with flooded suction conditions - are provided with suction casings of end suction design to obtain further reduction of NPSH values.
Suction Impeller
For lowering the NPSH value, the impeller of the first stage is designed as a suction impeller with enlarged impeller eye.
Antifriction Bearings
The drive shaft is carried in generously dimensioned antifriction bearings, grease filled for lifetime and protected by radial seal ring against environment. An oil mist or oil bath API-bearing housing is an option. The protection device avoids damage to the containment shell in case of worn out ball bearings.
Diffuser, Radial Loads
The impellers are centred inside of the diffusers. The diffusers are of multi-flow channel design. Therefore, no radial loads exist on the sleeve bearings.
Priming Stage
The side channel stage is capable to evacuate the suction line and therefore, to self-prime if initially filled with operating liquid. In the priming phase the side channel pump works as a positive displacement pump.
The displacement effect is created by a rotating liquid ring which enters and exits the side channel in a piston fashion by each rotation. This is generated by an interrupter in the side channel which separates suction and pressure area. The piston effect conveys the gas from suction to discharge side. The priming stage works automatically, no auxiliary vent equipment required.
When pumping LPG, attention has to be paid to gas entrainment, by vapour bubbles. In practice, these pumps can pump this liquid-gas-mixtures without auxiliary device. Due to the increased pressure in the side channel stage, the gas bubbles turn into liquid gas-phase again.
Monitoring
Connection for temperature detection element for containment shell surface temperature is available as standard. Dry running protection and monitoring of ball bearings and containment shell temperature with the patented 'MAG-SAFE' System is highly recommended.
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