Overload Tripping and Motor Overheating in Screw Pump Operation: Troubleshooting and Remedies

Overload Tripping and Motor Overheating in Screw Pump Operation: Troubleshooting and Remedies

Screw pumps are positive displacement pumps commonly used in lubrication systems, fuel transfer, hydraulic oil circulation, and high-viscosity media transport. A frequent operational failure is motor overload tripping accompanied by rapid motor temperature rise. This condition indicates excessive load, hydraulic imbalance, or mechanical resistance within the pump system. If not addressed promptly, it may lead to motor burnout, coupling damage, or internal pump seizure.

Overload Tripping Mechanism

Motor overload occurs when the required torque exceeds the rated motor capacity.

In screw pumps, torque demand is directly influenced by discharge pressure, fluid viscosity, internal friction, and mechanical condition of rotating components.

Overload tripping is fundamentally caused by excessive resistance in the hydraulic or mechanical system.

The motor protection system reacts to prevent thermal damage.

Excessive Discharge Pressure and System Backpressure

One of the most common causes is high system resistance.

Blocked pipelines, partially closed valves, or undersized discharge lines increase backpressure, forcing the pump to operate under overload conditions.

Faulty or incorrectly adjusted relief valves can also prevent proper pressure regulation.

As pressure rises, torque demand increases proportionally, leading to overheating and tripping.

High Fluid Viscosity and Low Temperature Conditions

Viscosity has a direct impact on pump load.

When temperature drops, fluid resistance increases significantly, requiring higher torque to move the medium.

High-viscosity conditions dramatically increase motor load and are a leading cause of cold-start overload tripping.

Incomplete preheating further worsens the condition.

Internal Mechanical Wear and Increased Friction

Wear of screws, bushings, or bearings increases internal friction.

This leads to higher energy losses and uneven mechanical resistance during rotation.

Severe wear may cause partial contact between components, further increasing torque demand.

Suction Restriction and Cavitation Effects

Insufficient suction or partial blockage causes incomplete filling of pump chambers.

This leads to cavitation, vibration, and unstable hydraulic loading, which increases motor current fluctuation.

Air ingress in suction lines also contributes to unstable operation.

Electrical and Drive System Issues

Motor overheating may also result from electrical abnormalities.

Low voltage supply, phase imbalance, or incorrect VFD parameter settings can reduce motor efficiency and increase current draw.

Overly aggressive acceleration or low-frequency operation under heavy load may also cause thermal stress.

Misalignment and Mechanical Installation Errors

Improper shaft alignment increases coupling stress and bearing load.

Even small angular or radial misalignment can significantly increase frictional losses and vibration.

Misalignment is a hidden contributor to persistent overload and motor heating issues.

Seal Friction and Auxiliary Load Increase

Mechanical seals generate additional frictional load.

Dry running or insufficient flushing increases seal face temperature and resistance, contributing to motor overload.

Seal failure may also lead to leakage and further system instability.

Diagnostic Procedure

A systematic approach is required for accurate troubleshooting:

First, check discharge pressure and pipeline condition. Second, verify fluid temperature and viscosity. Third, inspect suction line for blockage or air ingress. Fourth, evaluate motor voltage and current balance. Finally, assess internal wear condition and mechanical alignment.

Separating hydraulic overload from mechanical resistance is essential for correct diagnosis.

Corrective Measures

If caused by system backpressure, clean or redesign pipelines and adjust relief valve settings.

For high-viscosity fluids, implement preheating or insulation measures.

Worn internal components should be repaired or replaced to restore normal clearance.

Electrical issues should be corrected by adjusting motor protection settings or VFD parameters.

Alignment correction should be performed if vibration or coupling wear is detected.

Preventive Strategies

Regular monitoring of pressure, temperature, and current trends helps identify early overload conditions.

Proper system design, including adequate pipe sizing and relief protection, reduces risk of overload events.

Stable hydraulic conditions and correct viscosity control are key to preventing motor overheating.

Conclusion

Overload tripping and motor overheating in screw pumps are primarily caused by excessive system pressure, high viscosity, internal wear, suction restriction, misalignment, and electrical instability. A structured diagnostic and corrective approach is required to eliminate root causes. Maintaining balanced hydraulic load and stable mechanical alignment is essential for preventing overload failure and ensuring long-term motor reliability.

References

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

2. Hydraulic Institute Standards for Rotary Positive Displacement Pumps

3. API Recommended Practices for Pumping Systems and Motors

4. Machinery Electrical and Mechanical Failure Analysis Guide

5. Industrial Pump Operation and Maintenance Engineering Manual