A pump shaft is a major part whose function is to transmit input power from the driver to the impellers mounted on the shaft. It is subjected to several stresses flexural, shear, torsional, tensile, etc. Of these, the torsional stress is most significant and is usually used as basis for sizing the shaft diameter. The shaft position, horizontally or vertically, defines whether a pump is considered as a horizontal pump, or a vertical pump.
Shaft sizes are various which may be determined by torsional stress or shaft deflection consideration. However, there are other situations where the shaft size is determined by neither of them. If the rotor natural frequency at a given pump speed coincided with the natural frequency of other pump components, such as the bearing housing, the frequency is said to be in resonance. The pump speed at which the frequency is in resonance is called the critical speed of the pump.
Then a pump shaft bearing is a mechanical component used to support an applied load, and allow rotational or sliding motion between two or more parts. It is known as a rolling-element bearing. This type uses spheres or small cylinders that rotate, or roll, between a shaft and the mating parts to reduce friction and allow much tighter mechanical tolerances. A ball bearing is a common type of pump shaft bearing, with spheres that spin between the inner and outer races to reduce friction.
The three main components of a rolling-element bearing are the inner race, which contains the hole that the shaft slides into; the outer race, which is usually mounted inside housing; and the rolling, mechanical components located between the inner and outer races.
There are many different types of pump shaft bearings , ranging from simple, inexpensive bearings that provide sliding contact, to high-precision bearings for maintaining very precise, mechanical tolerances and high reliability. And various types can be widely used in mechanical and industrial applications, including automotive, aerospace, industrial machinery and so on.
In addition to various types, there are also different sizes and precisions. Thus selecting the appropriate bearing for a specific application is not very easy. Generally, it should based on several considerations, such as the rotational speed of operation, the type of applied loads, the size, weight, costs, and safety requirements, etc.
When compared to many other types, the higher precision pumps can provide much higher reliability and extended service intervals. Most bearings are produced to standardized tolerances established by international standards organizations, with consideration for the proper tolerances for the shaft and housing to ensure proper operation.