With cryogenic pumps and expanders, the submerged motor or generator is cooled and the bearings lubricated by a predetermined portion of the liquid being pumped. A small portion of the pumped fluid passes through the back wear ring of the highest pressure impeller or runner stage. This fluid is routed through the Thrust Equalizing Mechanism (TEM®
) to eliminate axial loads on the anti-friction bearings.
The operation of the TEM is simple. The upper wear ring (fixed orifice) is larger in diameter than the lower wear ring (fixed orifice), resulting in a net resultant force in the upper direction. Due to this upward force, the pump shaft and all of its rotating components move upward. This movement reduces the gap between the impeller and the stationary plate (variable orifice), thus restricting the wear ring leakage flow and causing the pressure in the upper chamber, inside the upper wear ring.
Due to increased pressure in the upper chamber, the thrust is reversed and now acts in a downward direction. This causes the rotating assembly to move downward, thereby opening the gap between the stationary plate and the impeller throttling ring, allowing the pressure in the upper chamber to decrease. The gap between the stationary plate and the impeller’s throttling ring then adjusts automatically to produce pressure in the upper chamber sufficient to offset the upward thrust. The end result is an equilibrium created between the upper and lower impeller surfaces to provide an extremely stable system with zero thrust loads on the bearings. This feature substantially increases the reliability and life span of the bearings and reduces equipment maintenance requirements.
The TEM is a means of removing thrust loads on bearings in submerged centrifugal pumps and expanders. The TEM is verified during performance testing
by the use of a proximity probe placed at the end of the shaft to measure actual axial movement. The validity of this approach has been demonstrated through thousands of pumps delivered and millions of hours of successful operation.