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Technical Specification for Machining, Inspection, and Acceptance of Shaft Components for Split Case Centrifugal Pumps
Split case centrifugal pumps are widely used in industries such as petrochemical processing and water conservancy. Shaft components are among the most critical parts of the pump, directly determining operating efficiency, reliability, and service life.
To ensure safe and stable operation of the equipment and to standardize the machining, inspection, and acceptance procedures for shaft components, this technical specification is established. It covers three key stages, as outlined below.
1. Shaft Machining Technical Requirements
Machining accuracy of shaft components forms the foundation for stable pump operation. The detailed machining requirements are shown in the table below:
| No. | Item | Technical Requirement |
| 1 | Surface roughness of shaft–bushing mating area | Ra ≤ 1.6 μm |
| 2 | Shaft and bushing fit tolerance | H7/h6 clearance fit (basic hole system) |
| 3 | Overall shaft surface quality | Surface shall be smooth, free from cracks, obvious wear, mechanical damage, scratches, and burrs |
| 4 | Keyway parallelism (split case double-suction pump) | Parallelism error between keyway centerline and shaft centerline ≤ 0.03 mm (over full length) |
| 5 | General shaft straightness | Shaft straightness deviation ≤ 0.013 mm/m |
| 6 | Journal surface condition of centrifugal oil pump shaft | Journal working surface shall be free from pitting, grooves, scoring, or surface spalling |
| 7 | Journal surface roughness of centrifugal oil pump shaft | Ra ≤ 0.8 μm |
| 8 | Geometric tolerances of centrifugal oil pump shaft journal | Roundness and cylindricity errors ≤ 0.02 mm |
In summary, shaft machining must ensure smooth, damage-free surfaces and precise dimensional control at critical locations to prevent abnormal operation caused by machining deviations.
2. Pre-Assembly Inspection Requirements
After machining is completed, shaft components shall undergo comprehensive inspection prior to assembly to eliminate defects and ensure safe installation. The inspection criteria are as follows:
| No. | Inspection Item | Acceptance Criteria |
| 1 | Shaft cleanliness | Shaft body (including journals, keyways, and mating surfaces) shall be thoroughly cleaned and free from oil, rust, chips, or foreign matter |
| 2 | General visual inspection | No cracks, severe wear, erosion, impact damage, or deformation |
| 3 | Dedicated inspection for split case double-suction pump shaft | Shaft body, journals, and keyway mating areas shall be free from cracks, abnormal wear, or signs of medium erosion |
| 4 | Defect management | Any nonconformities shall be documented in detail (location and size), with cause analysis and corrective measures |
| 5 | Straightness of low-speed shaft | Straightness deviation at mid-span ≤ 0.07 mm (over full length) |
| 6 | Straightness of high-speed shaft | Straightness deviation at mid-span ≤ 0.04 mm (over full length) |
| 7 | Straightness of centrifugal oil pump shaft | Overall shaft straightness deviation ≤ 0.05 mm |
Inspection focuses on cleanliness, surface integrity, and dimensional accuracy. Any detected issues must be recorded and resolved promptly to prevent nonconforming components from entering the assembly process.
3. Pre-Operation Acceptance Criteria
After assembly, final acceptance shall be performed prior to commissioning to ensure all requirements are met and the pump can be safely put into operation:
| No. | Acceptance Item | Acceptance Standard |
| 1 | Shaft–bushing fit condition | Compliance with H7/h6 tolerance; smooth manual rotation without binding, uneven wear, or abnormal noise |
| 2 | Shaft alignment condition | Shaft system coaxiality meets design requirements; smooth rotation with no abnormal resistance or radial runout |
| 3 | Keyway alignment (split case double-suction pump) | Parallelism error between keyway centerline and shaft centerline ≤ 0.03 mm (over full length) after assembly |
| 4 | Journal operating condition of centrifugal oil pump | Journal and bearing mating surfaces intact, free from pitting, scoring, scratches, or indentations |
| 5 | Verification of geometric and dimensional accuracy | Shaft straightness and journal roundness/cylindricity comply with the machining requirements of this specification |
| 6 | Acceptance documentation | All inspection records shall be complete, traceable, and approved by authorized inspectors prior to commissioning |
The core of acceptance is to confirm smooth shaft rotation, proper fit, undamaged critical surfaces, and complete inspection records. Only compliant equipment may be put into service to prevent operational failures.
4. Conclusion
Machining control, pre-assembly inspection, and pre-operation acceptance are the three critical stages for ensuring the safe and reliable operation of split case centrifugal pumps. Strict adherence to this specification can significantly improve shaft component quality, reduce equipment failures, extend service life, and ensure stable, efficient pump operation.
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