What are the best practices to design seals and bearings for centrifugal pumps?

1 Seal types and selection

The seal is the device that prevents leakage of the pumped fluid from the pump casing or the shaft. There are two main types of seals for centrifugal pumps: mechanical seals and packing seals. Mechanical seals consist of two mating surfaces that create a tight seal by contact pressure and friction. Packing seals use a flexible material, such as graphite or PTFE, that is compressed around the shaft and forms a seal by filling the gap. The selection of the seal type depends on several factors, such as the fluid properties, the operating conditions, the pump design, and the cost. Generally, mechanical seals are more reliable, efficient, and suitable for high-pressure, high-temperature, and corrosive fluids. However, they are also more expensive, complex, and sensitive to misalignment and vibration. Packing seals are simpler, cheaper, and more forgiving, but they require more maintenance, consume more power, and generate more heat and wear.

2 Bearing types and selection

The bearing is the component that supports the rotating shaft and reduces friction and wear. There are two main types of bearings for centrifugal pumps: rolling element bearings and plain bearings. Rolling element bearings use balls or rollers that roll between inner and outer rings. Plain bearings use a sliding surface that contacts the shaft directly or through a thin film of lubricant. The selection of the bearing type depends on several factors, such as the load, the speed, the lubrication, the temperature, and the noise. Generally, rolling element bearings are more suitable for high-speed, low-load, and low-temperature applications. They also have lower friction, higher accuracy, and longer life. However, they are also more expensive, noisy, and sensitive to contamination and misalignment. Plain bearings are more suitable for low-speed, high-load, and high-temperature applications. They also have lower noise, higher damping, and lower sensitivity to shock loads. However, they have higher friction, lower accuracy, and shorter life.

3 Seal and bearing design parameters

The design of seals and bearings for centrifugal pumps requires careful consideration of size, geometry, material, and configuration of the components. Key parameters to consider include the seal face width and diameter, which can affect contact pressure, heat generation, and leakage rate; the seal spring force and balance ratio, which can affect seal face loading, friction, and wear; the seal flush plan and arrangement, which can impact cooling, lubrication, and cleaning; the bearing clearance and preload, which can determine bearing stiffness, friction, and vibration; the bearing lubrication type and method, which can influence bearing temperature, wear, and life; and the bearing housing design and alignment, which can affect bearing support, stability, and load distribution.

5 Seal and bearing optimization and improvement

Optimizing and improving seals and bearings for centrifugal pumps is a way to enhance their performance, reduce cost, and extend life. Some of the techniques used for this are selecting seal face materials with better wear resistance, corrosion resistance, and compatibility with fluids; modifying seal face geometry to improve flatness, smoothness, and conformity; designing and modifying a seal flush system for improved cooling, lubrication, and cleaning; choosing bearing materials with better wear resistance, fatigue resistance, and durability; modifying bearing geometry for improved fit, alignment, and load distribution; and designing and modifying a bearing lubrication system for better cooling, lubrication, and cleaning.

6 Seal and bearing maintenance and troubleshooting

The maintenance and troubleshooting of seals and bearings for centrifugal pumps are essential to ensure their proper operation, prevent failures, and identify problems. Inspecting and replacing seals involves checking the condition, detecting signs of wear or damage, and replacing worn or defective parts. Seal adjustment and alignment requires setting the seal spring force, balancing the seal faces, and aligning the seal with the shaft and the pump. Seal flushing and cleaning includes supplying fresh fluid, removing debris, and preventing clogging or contamination of the seal faces. Additionally, bearing inspection and replacement involve checking the bearing condition, detecting signs of wear or damage, replacing worn or defective parts, supplying adequate lubricant, removing dirt, monitoring vibration, temperature, noise, and other parameters to diagnose faults. All of these activities are necessary to maintain a centrifugal pump's optimal performance.