HH 250 High‑Head Pump Impeller Back Blade Wear Pattern: Field Correction for Increased Clearance and Axial Thrust Imbalance

Subtitle: When back blade clearance increases from 1.5mm to 3mm, axial thrust rises 40% – feeler gauge measurement and hardfacing repair restore axial balance

Introduction

The HH 250 is a high‑head HH series slurry pump (250mm discharge) with single‑stage head up to 60‑80 meters, widely used in deep well dewatering and long‑distance tailings transport. The back blades (auxiliary vanes on the impeller back shroud) are critical for axial thrust balancing. However, after prolonged operation, radial and axial clearances increase due to wear, causing axial thrust imbalance. This overloads the thrust bearing, accelerates mechanical seal leakage, and can even cause axial shaft movement, leading to severe failure.

Hebei Xingou Machinery Equipment Co., Ltd. has found that wear‑induced clearance increase is often overlooked. This article describes back blade wear patterns, clearance measurement (feeler gauge), wear limits, and field repair methods (hardfacing + grinding) to restore axial balance and extend bearing and seal life.

1. Function and Wear Mechanism of Back Blades

1.1 Axial Thrust Balancing Principle

Due to uneven pressure distribution across the impeller, an axial thrust toward the suction side is generated. Back blades rotate with the impeller, imparting centrifugal force to the fluid in the back chamber, reducing back pressure and thus axial thrust. Clearances between the back blades and the pump cover (both axial and radial) directly affect balancing effectiveness.

1.2 Wear Locations and Rates

Trend: Wear is slow initially; once clearance exceeds a threshold, particles enter more easily, accelerating wear – a vicious cycle.

2. Effect of Clearance Increase on Axial Thrust

2.1 Clearance vs. Axial Thrust

Conclusion: Increasing clearance from 0.5mm to 2.5mm raises axial thrust by >70%, thrust bearing temperature by 27°C, and seal leakage risk dramatically.

2.2 Symptoms of Axial Thrust Imbalance

3. Field Measurement of Back Blade Clearance

3.1 Tools

3.2 Procedure

4. Wear Limits and Intervention Timing

5. Field Correction Methods

5.1 Hardfacing of Back Blades (Recommended)

When blade height is reduced or tips rounded, hardfacing restores dimensions.

5.2 Replace Pump Cover or Add Shims

If the pump cover mating surface is severely worn, replace the cover or add shims between cover and bearing housing to reduce clearance.

5.3 Adjust Impeller Axial Position

By changing the axial position of the bearing assembly (E/F type brackets), the clearance can be finetuned.

Hebei Xingou Machinery offers stainless steel shim kits.

6. Field Case

Background: An HH 250 pump at an iron mine had thrust bearing temperature of 88°C after 8,000 hours, with increased mechanical seal leakage. Inspection revealed severe wear of back blade tips; axial clearance was 2.8 mm (0.6 mm new).

Actions:

• Hardfaced back blades to restore original height.

• Ground to standard size; final clearance 0.7 mm.

• Thrust bearing (slightly worn) was replaced.

Results:

• Thrust bearing temperature dropped to 62°C.

• Seal leakage stopped.

• Pump has run stably for 1 year without axial thrust issues.

7. Maintenance Recommendations

Conclusion

Back blade wear leading to increased clearance is a hidden cause of axial thrust imbalance, thrust bearing overheating, and mechanical seal leakage on HH 250 high‑head pumps. By regularly measuring axial clearance (feeler gauge) and repairing when clearance reaches 1.5-2.0 mm (hardfacing or shim adjustment), axial balance can be restored, extending bearing and seal life 2‑3 times. Hebei Xingou Machinery Equipment Co., Ltd. offers back blade hardfacing and on‑site clearance adjustment services. Please contact us.