Operation & Maintenance of Power Plants
The attraction of magnetic couplings
Magnetic coupling meets challenging high inlet pressure lube oil pump applications. Thomas Flauger reports.
T
hree screw pumps are commonly used as lube oil pumps for compressors, gearboxes, turbines and other rotating equipment. Teir popularity stems from the efficient, reliable and long lasting
service they provide.
While most lube oil pumps are only exposed to ambient pressure at the pump inlet port there are some applications where the pump sees high inlet pressures. Tis poses a huge challenge for the pump seal solution and pump construction. In many pump designs it can also lead to high bearing and seal loads that negatively affect the pump and seal life.
Lube oil pumps High inlet pressure applications for lube oil pumps can be found in flooded screw compressors and turbo expanders. Te pressure of the lube oil entering the pump is at the same level as the compressed gas which can reach 100 bar or more.
Fig. 1. KRAL’s magnetic coupling pumps.
Such high inlet pressures can create high axial forces on the main pump drive screw (power rotor) that lead to high bearing loads.
Tis needs to be considered in the pump design.
Reinforced bearings, liquid channels for hydraulic balance, mechanical bracing and other measures tend to significantly increase the pump cost. Since the lube oil pump is used to boost the system
pressure of the lube oil by a few bar (around 5 to 15bar) the outlet pressure is not significantly higher. Tree screw pumps are often driven by an electric motor which is connected to the shaft of the main screw. Te shaft exits through the pump casing. Terefore the main screw must be sealed to prevent leakage.
Te most common sealing solution is a mechanical
seal. Due to the high inlet pressure, only special sealing arrangements, often with balanced mechanical seals, can achieve this task. Te pump cost is driven up even further.Tere is an innovative new approach to high inlet pressure
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