Bearings play a vital role in the smooth functioning of Centrifugal pumps in chemical plants. Bearings in centrifugal pumps support hydraulic loads imposed on the impeller, the mass of the impeller and shaft, and induced loads due to couplings and drive systems. They also help keep the shaft end-play and axial deflections within acceptable limits for the impeller and seal assembly. In addition, they reduce friction, which can result, if uncontrolled, in loss of power, excessive heat generation, increased noise and wear or early seal failure.

If and when pump bearings fail over time, they usually do so for root causes other than true metal fatigue. Causes can include impact damage sustained during assembly, contamination (both liquid and solid), excessive or reverse thrust loads, inadequate or ineffective lubrication, static vibration, insufficient loading, improper installation or misalignment.

All these influences suggest that the service life of pumps and their bearings can be maximized when bearing options are evaluated in the context of their designs and operating environments.

Single-row deep groove ball bearings are used most often in the radial position in nearly every centrifugal pump.

Identifying Requirements

In centrifugal pumps, which are classified as kinetic or dynamic pumps, energy is added continuously to the system. Compared with positive displacement pumps, which are used to move viscous fluids, centrifugal pumps exhibit relatively lower radial and axial loads, fewer moving parts, lower operating costs and minimal pressure pulsations. Typical bearing arrangements for these pumps include radial bearings to support radial loads and thrust bearings to support axial loads created by hydraulic forces in the pump.

Certain parameters initially can help guide the selection process such as external loads and direction, shaft and housing fits, as well as shaft material, and speed. These are reviewed below.

1. External Loads and Direction: The proper size and type of a bearing will hinge on its capacity to carry radial and thrust or axial loads. Bearings with low contact angles are designed primarily for radial loads. Bearings with higher contact angles are most suitable for thrust loads. In real-world pump applications, though, loads may vary from heavy to minimal and reverse direction. Applying an axial preload to the pair can promote adequate minimum thrust load for each bearing.

2. Shaft and Housing Fits: If the load-carrying capability of a bearing is to be realized fully, the inner and outer rings must be supported firmly and evenly around their complete circumference and across the whole width of the bearing raceway. The bearing rings alone cannot support the applied loads. The purpose of the rings is to pass that load to the shaft and housing so that they can support the applied forces. Rings must be reliably secured to prevent them from turning on or in their seatings under load. Inadequately or incorrectly secured bearing rings can damage the bearings and associated components.

3. Speed of Rolling Bearings: There is a limit to how fast rolling bearings can be operated. Generally, the limit will be governed by the operating temperature that can be permitted with respect to the lubricant being used or the material of the bearing components. Bearing type and size, internal design, load, lubrication and cooling conditions, cage design, precision tolerance class and mounted internal clearance all will determine permissible speed.

Whenever evaluating bearings for a particular pump application, the first rule of thumb is to understand that each type of bearing is designed for specific operating conditions and a particular bearing solution for one application may be inappropriate for another. Partnering at the outset with an experienced manufacturer can help chart the most appropriate decision-making course.

Radial Bearings :
Deep Groove Ball Bearings | Self Aligning Ball Bearings | Angular Contact Ball Bearings | Cylindrical Roller Bearings | Needle Roller Bearings | Spherical Roller Bearings | Taper Roller Bearings