Operation & Maintenance of Power Plants
applications that is able to meet the technical challenges and even provides lower cost solutions: magnetically coupled lube oil pumps. Compared to a mechanically sealed pump a magnetically coupled pump has no rotating seal. Te pump is hermetically sealed and leak-free. No seal maintenance or seal change is required leading to a much more reliable and durable pump. Te magnetic coupling does not wear and therefore
requires no maintenance under normal circumstances. Tis creates a better, more reliable pump solution at a lower cost.
How does it work? Te outer rotor – a magnetic assembly containing powerful permanent magnets – is attached to the motor shaft. Te pump housing and drive screw are hermetically sealed by a containment can (canister).
Drive screw: High inlet pressure acts directly on the face of the main drive screw as well as the idler screws. Some of the force is compensated on the pressure side of the main screw. However a resulting axial force would normally create a high axial load on the bearing. Not so in the case of a magnetic coupling. Balancing cylinder: Te balancing cylinder is exactly dimensioned so that the axial forces resulting from the pressures acting on its faces largely minimise the axial loads. Magnetic coupling: Due to a bore through the
centre of the drive screw the suction side pressure conditions are also present within the containment can of the magnetic coupling. Because of this special design a force is created
by the lube oil that compensates the residual axial thrust on the main spindle. Te load on the bearing is minimised leading to long, trouble free operation. In comparison on a mechanically sealed pump
the surface area of the shaft drive end is exposed to atmosphere and therefore no force can be created to counteract axial thrust.
l No more seal maintenance or seal change required; l Hermetically sealed – guaranteed leak free; l Hydraulically balanced due to axial thrust compensation (even at high inlet pressure);
l Long Bearing Life; l Completely enclosed – no air or moisture can enter pump and get in touch with the lube oil;
l Suited for high inlet pressure applications (compressor/expander lube oil pump).
Fig. 2.A big advantage of the magnetic coupling is the axial thrust compensation.
Te containment can is made from highest quality materials (Hastelloy, Titanium and others) to minimise eddy current losses thereby assuring high efficiency. It is also able to withstand the high pressure. Te inner rotor is attached to the pump shaft and contains strong and durable rare earth magnets. Te motor torque is transferred through the containment can (canister) without contact to the pump shaft through magnetic forces.
Axial thrust compensation Another huge advantage of the magnetic coupling is the axial thrust compensation. Te magnetic coupling design eliminates the axial force resulting in only minimal load on the ball bearing due to the geometrical conditions.
Life expectancy of the ball bearing is therefore independent from the inlet pressure. Te magnetic coupling replaces the costly mechanical seal. Tis creates a better, more reliable pump solution at a lower cost.
Environmental benefit Critical fluids containing substances endangering the health or the environment should not leak to the atmosphere. Even a perfectly working mechanical seal requires a certain amount of leakage to ensure proper lubrication of the rotating seal faces. In comparison to that a magnetically coupled pump is hermetically sealed eliminating any leak oil. Lube oil systems stay clean and no disposal of dripping oil is required. Magnetic couplings replace conventional shaft seals.
KRAL three screw pumps with magnetic coupling are hermetically sealed; the environment remains clean KRAL three screw pumps with magnetic couplings
are three screw pumps for pumping fuels, oils and other non aggressive liquids. Tey are used primarily in industrial applications, such as: power plant engineering, as circulation three screw pumps for fuels; marine, as circulation three screw pumps for fuels; plastics processing, especially polyurethane applications; and plant engineering and the chemical industry for heat transfer fluids. l
For more information ✔ at
www.engineerlive.com/ipe
Thomas Flauger is with KRAL AG, Lustenau, Austria.
www.KRAL.at
www.engineerlive.com 31
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