How Does Volumetric Efficiency Decline in Progressive Cavity Pumps? A Step-by-Step Analysis

 How Does Volumetric Efficiency Decline in Progressive Cavity Pumps? A Step-by-Step Analysis

In industrial fluid handling systems, progressive cavity pump (also known as screw pumps) are widely used for transferring viscous, abrasive, and sensitive fluids due to their stable flow and high adaptability.

However, during long-term operation, many users notice a common issue:

👉 The pump runs normally, but the flow rate gradually decreases.

This is not a sudden failure — it is typically the result of a gradual decline in volumetric efficiency.

What Is Volumetric Efficiency?

Volumetric efficiency refers to:

👉 Actual flow rate ÷ Theoretical flow rate

When internal leakage or slippage increases, the pump delivers less fluid than expected, leading to efficiency loss.

The Step-by-Step Formation of Efficiency Decline

Understanding how this decline develops is key to preventing costly failures.

1. Initial Stage: Micro Wear Begins

At the early stage of operation:

Slight wear occurs between rotor and stator

Sealing interference begins to weaken

👉 At this point:

Performance appears normal, but internal leakage has already started

2. Progressive Stage: Leakage Increases

As operation continues:

Clearance between rotor and stator increases

Fluid starts to slip from high-pressure zones to low-pressure zones

👉 Result:

Slight drop in flow rate

Reduced pressure stability

Internal leakage is one of the main factors affecting volumetric efficiency.

3. Acceleration Stage: Sealing Performance Degrades

With further wear:

Stator elasticity declines

Rotor-stator fit deteriorates

👉 Result:

Significant increase in slippage

Rapid drop in volumetric efficiency

Wear of internal components is a major cause of performance loss.

4. Failure Stage: Pump Loses Effective Output

At the final stage:

Sealing function is nearly lost

Internal circulation dominates

👉 Symptoms:

Pump rotates normally but delivers little flow

Pressure cannot be maintained

Key Factors Accelerating Efficiency Decline

Several operating conditions can speed up this process:

Abrasive or particle-laden fluids → Increased wear

Dry running → Severe stator damage

High pressure → Increased leakage due to deformation

Improper fluid properties (viscosity mismatch) → Higher internal friction

Practical Impact on System Performance

Declining volumetric efficiency leads to:

Reduced pumping capacity

Increased energy consumption

Higher maintenance frequency

Shortened equipment lifespan

In many cases, the pump is still running — but doing ineffective work.

How to Prevent or Slow Down Efficiency Loss

To maintain performance, consider the following:

✔ Avoid dry running (critical)

✔ Select materials suitable for the fluid

✔ Control operating pressure and speed

✔ Monitor flow rate changes regularly

✔ Replace worn stator/rotor components in time

Further Technical Reference

For a more detailed technical explanation and real-world solutions, you can refer to:

👉 https://www.scpv.cn/news/387.html

Conclusion

The decline of volumetric efficiency in progressive cavity pumps is not a sudden failure, but a progressive process:

👉 Micro wear → Internal leakage → Accelerated slippage → Functional failure

Understanding this evolution helps operators take action early, reduce downtime, and optimize system performance.

In practical applications, experienced manufacturers such as Shanghai Shangcheng Pump & Valve often emphasize proper selection and operation strategies to minimize efficiency loss from the very beginning.