A centrifugal pump is a common component of fluid transportation applications, and such devices move fluids through the conversion of rotational kinetic energy to hydrodynamic energy. With the use of an engine or electrical motor, the rotational energy needed for the pump’s operations can be supplied for accelerating fluids so that they flow radially outward into a diffuser or volute chamber. While centrifugal pump parts commonly serve many pumping applications due to their high flow rate capabilities, their performance can be negatively affected by axial thrust.
Regarding pump parts, an axial thrust load is commonly caused by an unequal distribution of pressure that exists between the front and back shrouds of the impeller. As the fluid is rotated by the impeller assembly, discharge pressure is produced through a centrifugal effect. As there is a difference in the suction and discharge pressure, an axial thrust force will begin to act against the impeller. While axial thrust can reduce the overall efficiency and performance of a particular pump, it can also present hazards to motor bearings as their service lives are shortened.
In order to cut down on centrifugal pump axial thrust, the most common solution is to redesign the impeller pump assembly to remove its asymmetry. As the various clearances within the assembly are filled with fluid at high pressure, this pressure can begin to act against the impeller and a net thrust will form in the opposite direction of the fluid flow. By removing the areas of the impeller shroud where the most amount of pressure builds, the pressure imbalance within the assembly can be reduced to deter the generation of axial thrust. While deterrence may vary, some designs have been capable of reducing upwards of 88% of the axial thrust caused by pressure imbalances.
While asymmetry and pressure imbalances are common causes of axial thrust, so too is the failure of the thrust compensating disc or transient and cyclic rotor axial excursions. To determine whether there is an axial thrust issue occurring in a centrifugal pump, common signs include high bearing temperatures, reduced pump flow, increased vibrations, failure of thrust bearings or discs, the premature failure of thrust bearing loads, and excessive wear present on pump clearances.
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