150ZJ-50 Slurry Pump Double Volute Design: Radial Force Balancing and Bearing Load Reduction

Subtitle: Double volute reduces radial force by 50%-70%, extends bearing life by 30%-50% – CFD analysis and field measurement data

Introduction

The 150ZJ-50 is a medium‑to‑large flow ZJ series slurry pump (150mm discharge, 500mm impeller diameter), widely used in coal preparation and fine tailings transport. When a pump operates away from its best efficiency point (BEP), pressure distribution around the impeller becomes uneven, generating a radial force on the impeller. This force is transmitted directly to the bearings, accelerating wear and potentially causing shaft bending and mechanical seal leakage. Conventional single‑volute pumps experience a sharp increase in radial force away from BEP. In contrast, the double volute design uses two symmetrical volute chambers to effectively balance radial force, significantly reducing bearing load.

Hebei Xingou Machinery Equipment Co., Ltd. has compared radial force distribution, bearing life, and vibration levels between single‑volute and double‑volute designs using computational fluid dynamics (CFD) and field measurements. This article explains the principle of radial force balancing in double volutes, presents test data, and demonstrates the real‑world benefits for bearing life extension.

1. Mechanism of Radial Force Generation

At the design flow (BEP), pressure distribution around the impeller is relatively uniform, and the net force is near zero. When the pump operates away from BEP, the velocity triangle at the impeller discharge changes, creating an uneven pressure distribution inside the volute. This generates a resultant force acting on the impeller – the radial force.

In a single‑volute pump, radial force is roughly proportional to the flow deviation. In a double‑volute pump, the two symmetrical volute chambers make the pressure distribution much more uniform, greatly reducing radial force.

2. Double Volute Structure and Balancing Principle

2.1 Structural Features

A double‑volute pump has two symmetrical volute chambers spaced 180° apart. Each chamber collects fluid from different phases of the impeller, and the streams merge at the discharge. This symmetrical arrangement creates a more uniform pressure field around the impeller.

Comparison with single volute:

2.2 Balancing Principle

In a double volute, the pressure fields from the two symmetrical chambers tend to cancel each other. Even away from BEP, pressure changes in the two chambers are similar but opposite in direction, so the net force on the impeller is greatly reduced. Studies show that double‑volute designs reduce radial force by 50%-70%, especially at off‑BEP conditions.

3. CFD Simulation Comparison

Hebei Xingou Machinery performed CFD simulations on the 150ZJ-50 pump with both single‑volute and double‑volute designs, comparing radial force at various flow rates.

Simulation conditions:

• Design flow Q* = 400 m³/h

• Rated speed 980 rpm

• Medium: clean water

Conclusion: The double volute reduces radial force by over 60% at off‑BEP conditions. At or near BEP, the difference is small. For applications where flow frequently varies (cyclone feed, tailings transport), the double volute offers a clear advantage.

4. Impact on Bearing Load and Life

4.1 Bearing Load Calculation

Bearing life is inversely proportional to the third power of load for ball bearings (or 10/3 power for roller bearings). Reducing radial force by 60% can theoretically extend bearing life several times.

For example, using the spherical roller bearing (e.g., 22324) commonly found in the 150ZJ-50, when radial force decreases from 1850 N to 620 N (a 66% reduction), the equivalent dynamic load P drops to about 33.5% of the original. The theoretical L10 life increase factor is approximately (1/0.335)^(10/3) ≈ 8‑10 times. However, actual measured life improvement, accounting for axial loads and other factors, is typically 30%-50%.

4.2 Field Measurement Comparison

Hebei Xingou Machinery conducted a field test at a coal preparation plant with two 150ZJ-50 pumps operating under identical conditions:

• Pump A: single volute

• Pump B: double volute

Both pumps ran at similar flows (average 360 m³/h) and same speed for 6 months. Bearing vibration and temperature were recorded.

Conclusion: The double‑volute design significantly reduces bearing vibration and temperature, extending bearing life by approximately 50%.

5. Other Benefits of Double Volute Design

Beyond radial force reduction and bearing life extension, the double volute offers additional advantages:

The double volute is especially valuable in applications with frequent flow changes, such as cyclone feed, filter press feed, and tailings transport where concentration varies.

6. Application Guidance and Selection Recommendations

Hebei Xingou Machinery equips all standard 150ZJ-50 pumps with a double‑volute design (single‑volute available upon request), ensuring long‑term reliability under varying operating conditions.

7. Case Study: Single‑Volute to Double‑Volute Retrofit at a Coal Preparation Plant

Background: A 150ZJ-50 pump used for cyclone feed at a coal preparation plant experienced frequent flow fluctuations between 280 and 450 m³/h. The original single‑volute pump had two bearing failures within one year, with vibration levels consistently above 5 mm/s.

Retrofit: The pump was retrofitted with a double‑volute casing (retaining the original impeller, shaft, and bearings). Hebei Xingou Machinery assisted with on‑site installation and commissioning.

Results:

• Bearing vibration reduced from 5.2 mm/s to 2.6 mm/s (-50%)

• Bearing temperature dropped from 78°C to 59°C

• The pump has operated for 16 months since retrofit without any bearing replacement

Economic benefit: Eliminated two bearing replacements per year, saving approximately $1,500 in parts and labor, plus about $800 in electricity savings from reduced friction due to lower vibration.

Conclusion

The double‑volute design of the 150ZJ-50 slurry pump effectively balances the radial force generated by the impeller at off‑design conditions, reducing radial force by 50%-70% and extending bearing life by 30%-50%. Double‑volute pumps also exhibit lower vibration, cooler bearings, and smoother operation, making them ideal for applications with frequent flow fluctuations such as coal preparation cyclone feed and tailings transport. Although the double‑volute casing is slightly more expensive to cast, its total lifecycle economic benefit significantly outweighs that of a single‑volute pump.

Hebei Xingou Machinery Equipment Co., Ltd. manufactures 150ZJ-50 slurry pumps with an optimized double‑volute design and offers custom selection based on your specific duty. For radial force analysis or bearing life calculations, please contact our technical team.