CDL Vertical Stainless Steel Multistage Pump: Impact of Internal Leakage on Overall Performance

 CDL Vertical Stainless Steel Multistage Pump: Impact of Internal Leakage on Overall Performance

In water supply boosting, industrial circulation, and water treatment systems, the CDL vertical stainless steel multistage pump is widely used for its compact design, stable operation, and high efficiency. However, after long-term operation, a critical yet often overlooked issue emerges — internal leakage.

It’s important to understand:

👉 Internal leakage is not a sudden failure, but the starting point of performance degradation.

For product details and specifications, visit:

👉 https://www.scpv.cn/pumps/CDL.html

1. Why Internal Leakage Exists in Multistage Pumps

Multistage pumps like CDL rely on multiple impellers to increase pressure step by step. Due to structural requirements, small clearances must exist between components:

Impeller and diffuser

Wear rings (clearance seals)

Shaft sleeve and sealing areas

These clearances are necessary for operation, but they also create natural leakage paths.

2. What Is Internal Leakage?

Internal leakage does NOT mean visible external leakage.

👉 It refers to:

High-pressure fluid flowing back to low-pressure zones inside the pump

Typical locations:

Impeller wear ring clearance

Diffuser passages

Shaft sealing areas

This results in fluid circulating inside the pump instead of being delivered outward.

3. Key Impacts on Pump Performance

3.1 Reduced Effective Flow Rate

Actual output flow decreases

End-user supply becomes insufficient

System compensation increases

👉 In essence:

Part of the flow is “lost” internally

3.2 Head Reduction (Critical in Multistage Pumps)

CDL pumps depend on cumulative head from each stage:

Leakage in early stages reduces energy for later stages

The effect compounds across multiple stages

👉 Result:

Significant head loss, not just minor reduction

3.3 Efficiency Drop and Higher Energy Consumption

Internal leakage creates recirculation flow, leading to:

Increased motor load

Reduced useful output

Lower hydraulic efficiency

Typical symptoms:

Higher current draw

Increased power consumption

Rising operating costs

👉 Simply put:

More energy is consumed for less output

3.4 Mechanical and System Instability

Disturbed internal flow leads to:

Hydraulic imbalance

Axial force fluctuations

Increased turbulence

Which can cause:

Faster bearing wear

Mechanical seal damage

Vibration and noise

👉 The issue escalates from performance loss to mechanical risk

4. Why Multistage Pumps Are More Sensitive

Compared to single-stage pumps:

More stages → cumulative leakage effect

Longer flow path → higher energy loss

Higher precision requirement → more sensitive to wear

Especially under:

Continuous operation

Slightly corrosive liquids

Fluids with fine particles

👉 Internal leakage develops faster and impacts more severely

5. How to Control Internal Leakage

✔ Proper Operation

Avoid long-term low-flow operation

Operate near the Best Efficiency Point (BEP)

✔ Routine Maintenance

Check wear ring clearances

Inspect diffuser and impeller wear

Monitor sealing components

✔ Selection and Configuration

Choose high-precision manufacturing

Use wear-resistant materials where needed

Match pump with system conditions properly

6. Conclusion

Many users attribute CDL pump performance decline to “aging,” but in reality:

👉 Internal leakage is the root cause behind most efficiency loss

It develops gradually, silently reducing performance until it affects the entire system.

Understanding and managing internal leakage is far more effective than simply replacing equipment — and it is the key to ensuring long-term, stable pump operation.