How to Inspect the Split Case Pump Shaft and Overhaul

The shaft is a critical rotating component in a split case pump, responsible for transmitting power from the motor to the impeller via the coupling. As the impeller rotates at high speed, it generates centrifugal force that propels liquid from the pump’s center to its periphery, creating a low-pressure zone at the impeller eye. Due to the pressure differential, fluid is continuously drawn into the pump. To maintain optimal performance and reliability, the shaft of a split case pump should undergo scheduled inspections and overhauls based on equipment condition and operational history.

Shaft Overhaul Requirements and Specifications

1. The surface roughness of the shaft bushing should be Ra ≤ 1.6 μm.

2. The shaft and bushing should fit within H7/h6 tolerance levels.

3. The shaft surface must be smooth, without cracks, visible wear, or damage.

4. The parallelism error between the keyway centerline and the shaft centerline of the split case pump must be less than 0.03 mm.

5. Shaft straightness and allowable bending tolerances:

– General shaft diameter: ≤ 0.013 mm

– Middle section of low-speed shaft: ≤ 0.07 mm

– Middle section of high-speed shaft: ≤ 0.04 mm

6. The shaft of the double-suction split case pump should be thoroughly cleaned and inspected. It must be free from cracks, significant wear, or erosion. Any defects should be documented in detail with cause analysis.

7. For centrifugal oil pumps, the shaft straightness should not exceed 0.05 mm over its full length. The journal must be free of pitting, grooves, or other surface damage. Surface roughness should be ≤ 0.8 μm, and journal roundness/cylindricity errors must be < 0.02 mm.

Conclusion

Proper shaft overhaul is essential to ensuring the reliability, efficiency, and safety of split case pump operation. Following dimensional and surface specifications during inspection and maintenance helps prevent failures and prolongs pump lifespan.