HH 200 High‑Head Pump Impeller Back Blade Optimization: Reducing Axial Thrust and Mechanical Seal Load

Subtitle: Increase back blade height from 5mm to 8mm, optimize angle to 15°, reduce axial thrust by 30%, double mechanical seal life

Introduction

The HH 200 is a large‑flow, high‑head HH series slurry pump (200mm discharge) with single‑stage head up to 60‑80 meters, widely used in deep well dewatering and long‑distance tailings transport. In high‑head pumps, pressure distribution is uneven across the impeller, creating an axial thrust directed toward the suction side. This thrust is transmitted through the shaft to the thrust bearing and mechanical seal, accelerating bearing wear and causing abnormal seal face loading, leading to leakage.

Impeller back blades (also called auxiliary vanes) are an effective structure for balancing axial thrust. By adding radial vanes on the impeller back shroud, centrifugal force reduces pressure in the back chamber, thus lowering axial thrust. Hebei Xingou Machinery Equipment Co., Ltd. has found through field practice that optimizing back blade height, number, angle, and clearance significantly reduces axial thrust and mechanical seal load. This article presents an optimization for HH 200 pump impeller back blades, supported by CFD simulations and field test data.

1. Axial Thrust Mechanism and Hazards

1.1 Source of Axial Thrust

During pump operation, pressure distribution differs across the impeller:

• Front side (suction side) – lower pressure

• Back side (shroud side) – higher pressure (close to discharge pressure)

The pressure difference creates an axial thrust from back to front (toward the suction side). For HH 200 pumps, this thrust can reach several thousand Newtons.

1.2 Hazards of Axial Thrust

2. Working Principle of Back Blades

Back blades are a set of radial straight or curved vanes cast on the impeller back shroud. As the impeller rotates, the back blades impart centrifugal force to the liquid in the back chamber, forcing it outward, reducing back chamber pressure, thus reducing the pressure difference and balancing part of the axial thrust.

Key parameters:

• Back blade height h

• Number of back blades z

• Back blade angle θ (relative to radial direction)

• Axial clearance δ between back blades and pump cover

3. Back Blade Optimization Plan

3.1 Height Optimization

Hebei Xingou Machinery’s CFD simulation showed that increasing back blade height from 5 mm to 8 mm further reduces back chamber pressure and reduces axial thrust by about 20%. Height beyond 10 mm gives diminishing returns and increases casting difficulty/cost. Therefore, 8 mm is recommended.

3.2 Angle Optimization

Radial blades (0°) direct centrifugal force purely radially, which is less efficient for pressure reduction. Backward curved blades (15°-20°) allow smoother liquid flow, improving centrifugal efficiency. Simulation shows that a 15° angle reduces axial thrust by an additional 10% compared to radial blades.

3.3 Clearance Optimization

The axial clearance δ between blade tips and the pump cover directly affects sealing effectiveness. Too small risks rubbing; too large causes leakage. Optimized clearance should be controlled at 1.0‑1.5 mm.

3.4 Combined Effect

4. Axial Thrust Calculation and Validation

4.1 Theoretical Calculation

Axial thrust F_ax is related to the pressure difference across the impeller and impeller geometry. With back blades reducing back chamber pressure, the thrust can be approximated as:

F_ax = ΔP × A_rim - F_back_blade

Where ΔP is the pressure difference, A_rim is the hub area, and F_back_blade is the balancing force from the back blades.

Hebei Xingou Machinery measured axial thrust on an HH 200 pump: with original back blades (h=5mm, 0°), axial thrust was ~3200 N; after optimization (h=8mm, 15°), thrust dropped to 2200 N – a 31% reduction.

4.2 Field Test Comparison

5. Mechanism of Reduced Mechanical Seal Load

Mechanical seal face specific pressure Pc is determined by spring pressure + medium pressure – fluid film reaction. Axial thrust adds an extra axial load to the seal, increasing face pressure and accelerating wear. After back blades balance part of the axial thrust, the axial component on the seal is reduced, the face pressure returns to design value, and both leakage rate and wear rate drop.

Hebei Xingou Machinery monitored seal chamber pressure fluctuation using an oscilloscope. After optimization, pressure fluctuation amplitude dropped from ±0.3 MPa to ±0.1 MPa, indicating much smoother operation.

6. Applicability and Precautions

6.1 Suitable Applications

• High‑head pumps (single‑stage head >50 m)

• High‑speed pumps (n >1200 rpm)

• Sites where axial thrust causes frequent bearing damage or seal leakage

6.2 Precautions

Hebei Xingou Machinery offers back blade optimization design and field retrofit services, including disassembly, measurement, new impeller customisation, installation, and commissioning.

7. Case Study: HH 200 Back Blade Optimization at an Iron Mine

Background: An HH 200 pump used for mine dewatering had thrust bearing temperature of 85°C after 3,000 hours, and mechanical seal leakage of 30 ml/h. Inspection revealed back blade height only 4.5 mm with radial straight vanes.

Retrofit: Replaced impeller with optimized back blades (height 8 mm, angle 15°), set clearance to 1.2 mm.

Results:

• Thrust bearing temperature dropped to 58°C

• Mechanical seal leakage reduced to 2 ml/h

• Pump has run for 18 months without further bearing or seal replacement

• Annual maintenance cost reduced by approximately $1,500

Conclusion

Optimizing back blades on HH 200 high‑head pump impellers (height from 5 mm to 8 mm, angle from 0° to 15°, clearance 1.0‑1.5 mm) reduces axial thrust by about 30%, more than doubles mechanical seal life, and significantly lowers bearing temperature. This low‑cost, quick‑payback retrofit is especially valuable for extending pump life in high‑head, high‑speed applications. Hebei Xingou Machinery Equipment Co., Ltd. provides back blade optimization design and on‑site retrofit services. Contact us for a custom solution.