Troubleshooting Low Pressure and Failure to Build Pressure in Screw Pumps

Troubleshooting Low Pressure and Failure to Build Pressure in Screw Pumps

Screw pumps, including single-screw and triple-screw types, are widely used in oil transfer, lubrication systems, chemical processing, and high-viscosity fluid transportation. As positive displacement pumps, they are expected to generate stable discharge pressure. However, in practical operation, users may encounter a situation where the pump runs normally but cannot build sufficient pressure. This issue is typically caused by internal leakage, suction limitations, system bypass conditions, or mechanical wear.

Internal Wear and Increased Leakage Clearance

One of the most common causes of pressure loss is internal wear.

As the rotor, stator, or screw elements wear over time, the sealing clearance between moving parts increases. This allows fluid to leak internally from the high-pressure side back to the low-pressure side, preventing pressure buildup.

Internal leakage directly reduces pressure capability even if pump speed and flow appear normal.

This condition develops gradually and is often mistaken for system pipeline problems.

Relief Valve or Bypass Valve Stuck Open

Many screw pump systems are equipped with a safety relief or bypass valve.

If this valve is stuck open, improperly adjusted, or damaged, a large portion of the pumped fluid will circulate back to the suction side or tank instead of building discharge pressure.

Contamination, spring fatigue, or improper installation are common causes of valve malfunction.

Suction Side Air Ingress or Poor Filling

Insufficient suction conditions can prevent the pump from fully filling its cavities.

Air leakage in suction pipelines, loose flange connections, or damaged seals can introduce gas into the system. Gas compressibility prevents effective pressure transmission.

Air entrainment significantly reduces the pump’s ability to generate stable discharge pressure.

Low inlet pressure or excessive suction lift can also contribute to incomplete chamber filling.

Excessive Fluid Viscosity or Temperature Deviation

Fluid properties have a strong impact on pressure performance.

If viscosity becomes too high due to low temperature, suction resistance increases and volumetric filling becomes incomplete. Conversely, extremely low viscosity increases internal slip and reduces pressure retention.

Maintaining the correct operating temperature is essential for stable pressure generation.

Rotor or Stator Damage in Progressive Cavity Pumps

In progressive cavity screw pumps, rotor and stator integrity is critical.

Stator wear, swelling, chemical degradation, or rotor surface damage can significantly reduce sealing effectiveness. This leads to increased internal backflow and inability to build pressure.

Even minor elastomer damage can cause significant performance loss.

Speed or Drive System Issues

Pump pressure is partially dependent on rotational speed and system resistance.

If motor speed is lower than design value due to frequency converter settings, belt slippage, or electrical faults, the pump may not generate sufficient discharge pressure.

Incorrect speed calibration is a frequently overlooked issue.

Pipeline Leakage or System Pressure Loss

External system leaks or improperly sealed connections can prevent pressure buildup.

Check valves installed in the wrong direction or malfunctioning valves may also allow backflow, reducing effective system pressure.

System integrity must be confirmed before diagnosing internal pump failure.

Gas Lock or Cavitation Phenomenon

When gas accumulates inside the pump chamber, it compresses instead of transmitting pressure.

This condition, known as gas lock, severely reduces pump efficiency and pressure output. It is often caused by poor suction conditions or volatile fluids.

Cavitation can also damage internal components and further reduce performance.

Diagnostic Procedure

A structured troubleshooting approach should be used.

First, verify motor speed and electrical input. Second, check suction conditions and confirm absence of air leakage. Third, inspect relief valve status. Fourth, evaluate fluid viscosity and temperature. Finally, assess internal wear through pressure-flow comparison tests.

Separating system issues from mechanical wear is essential for accurate diagnosis and cost-effective maintenance.

Preventive Maintenance Measures

Regular inspection of relief valves, maintaining proper suction conditions, controlling fluid temperature, and monitoring wear components can significantly reduce pressure-related failures.

Installing filtration systems and performing periodic performance testing also improves long-term reliability.

Conclusion

Failure of screw pumps to build pressure is typically caused by internal wear, bypass valve malfunction, suction air ingress, fluid property mismatch, speed deviation, or system leakage. A systematic diagnostic approach combined with proper maintenance practices is essential for restoring normal operation. Maintaining sealing integrity and stable operating conditions is the key to ensuring reliable pressure performance in screw pump systems.

References

1. Pump Handbook, Fourth Edition, McGraw-Hill Education

2. Hydraulic Institute Standards for Positive Displacement Pumps

3. API Recommended Practices for Screw Pump Systems

4. Industrial Progressive Cavity Pump Troubleshooting Guide

5. Machinery Reliability and Fluid System Engineering Manual