Hydraulic System - Oil Pump: Inspection & Maintenance Guide

Regular maintenance of the hydraulic oil pump is crucial for ensuring system reliability and longevity. Here’s a structured guide to inspecting and repairing key components of the pump.

Inspection Checklist

Pump Shaft: Check for bending. Replace if deformation is found.

Stator: Inspect the inner surface for wear or step-like indentations. Grind the inner chamber if irregularities are detected.

Valve Plate: Look for wear or pitting. Polish or grind grooves as necessary.

Bearings: Check for damage. Replace immediately if faulty.

Shaft Seal: Inspect for wear or failure. Replace promptly if compromised.

Step-by-Step Repair Procedures

1. Stator Repair

Method A: Grinding (for minor wear)

Use an internal grinder to refinish the stator’s inner surface.

Employ profile grinding to maintain the original cam-shaped contour.

Post-grinding surface roughness (Ra) must be < 0.63 μm.

Method B: Repositioning Wear Zones

The stator inner surface has two pressure and two suction zones. The suction zones typically experience the most wear due to centrifugal force and hydraulic pressure.

For stators with two dowel pin holes: Simply swap the stator 180° to reposition worn suction zones to pressure duty.

For stators with one dowel pin hole: Drill a new dowel pin hole symmetrically opposite the original, then rotate the stator 180°.

Replacement Criteria

Replace the stator if wear is severe and grinding proves ineffective.

New stators are typically made from high-carbon chromium bearing steel (GCr15), heat-treated to 60–65 HRC.

2. Rotor Repair

Minor Scratches: Polish with fine honing stones or lapping paste.

Severe Wear: Regrind the end faces on a cylindrical grinder.

Post-repair Specifications:

Surface roughness (Ra): < 0.63 μm

End face perpendicularity to centerline: ≤ 0.01 mm

Parallelism between end faces: ≤ 0.008 mm

Vane Slot Repair: Polish with fine honing stones. For heavy wear, regrind with a thin grinding wheel and fit new vanes. Clearance should be maintained between 0.013–0.018 mm.

3. Vane Repair

Polish vanes or re-dress chamfers if wear is observed.

Address issues like sticking or sluggish movement in rotor slots through lapping.

4. Valve Plate Repair

Light Scratches: Lap on a surface plate.

Severe Wear: Skim the end face on a lathe.

Post-machining Tolerances:

Parallelism and perpendicularity to the center hole: < 0.01 mm

Ensure machining does not compromise the structural strength of the plate.