ZJL 50 Vertical Slurry Pump Pit Bottom Anti‑Settling Retrofit: Effect of Agitator Speed and Blade Shape on Suspension Capacity

Subtitle: Reduce agitator speed from 1450 rpm to 980 rpm, change straight blades to backward‑curved blades – pit bottom sediment reduced by 65%, pump run cycle extended from 3 days to 10 days

Introduction

The ZJL 50 is a small vertical slurry pump (50mm discharge) in the ZJL series, widely used in small slurry pits, chemical tanks, and settling sumps. These pits are typically small (2-10 m³) with fluctuating liquid levels and lack external agitation. Solids settle rapidly, leading to pump suction blockage, impeller jamming, and even pump burial. Manual cleaning every 2-3 days is common – labor‑intensive and disruptive.

The ZJL 50 can be equipped with a bottom agitator that uses rotating blades to stir settled solids. However, the factory‑set agitator speed and blade shape are often not optimized for specific pit geometries, limiting effectiveness. Hebei Xingou Machinery Equipment Co., Ltd. has found through field tests that reducing agitator speed (from 1450 rpm to 980 rpm) and changing blade shape (from straight to backward‑curved) significantly improves suspension capacity and reduces sediment accumulation. This article presents test data, optimal parameters, and field retrofit procedures.

1. Sedimentation Problems in Small Slurry Pits

Small slurry pits (2-10 m³) have the following characteristics:

Typical consequence: After 2-3 days, sediment thickness reaches 200-300 mm, burying the pump suction, causing flow drop and motor overload trip.

2. Agitator Working Principle for Anti‑Settling and Key Parameters

The ZJL 50 bottom agitator rotates coaxially with the pump shaft, producing downward and radial jets that lift settled solids. Key parameters affecting suspension capacity:

Original configuration: speed 1450 rpm, straight radial blades, installation height 200 mm. Hebei Xingou Machinery proposed an optimized plan based on field tests.

3. Speed Comparison Test: 1450 rpm vs. 980 rpm

Test conditions: same pit (3 m³, depth 1.2 m, tailings slurry 30% solids).

Conclusion: Reducing speed actually increased bottom velocity and mixing radius. Reason: at 1450 rpm, intense turbulence near the blades dissipated energy quickly; at 980 rpm, flow was smoother, energy was used more effectively to promote horizontal diffusion.

4. Blade Shape Comparison: Straight vs. Backward‑Curved

Conclusion: Backward‑curved blades produce a downward jet component that directly impacts the pit bottom, lifting settled solids, and also provide wider radial coverage, reducing dead zones by >50%.

5. Optimized Configuration and Retrofit Results

5.1 Optimal Parameters

5.2 Retrofit Results at a Concentrator Chemical Tank (2.5 m³, depth 1.1 m)

6. Field Retrofit Procedure

7. Precautions

Conclusion

Sedimentation in small slurry pits with ZJL 50 vertical pumps can be effectively addressed by optimizing agitator speed and blade shape. Reducing speed from 1450 rpm to 980 rpm, changing straight blades to 15° backward‑curved blades, and lowering installation height to 70 mm increases bottom velocity by >30%, reduces sediment by 65%, and extends pump run cycle from 3 days to 10 days. This retrofit requires only pulley replacement (or VFD addition) and blade modification – low cost, quick payoff. Hebei Xingou Machinery Equipment Co., Ltd. offers on‑site anti‑settling retrofit guidance. Please contact us.