How to Inspect Screw Pump Stators for Wear
Introduction
Screw pumps are widely used in various industries due to their ability to handle viscous, abrasive, and high-solid-content fluids. The stator, typically made of elastomeric material, is a critical component that works in conjunction with the rotor to create the pumping action. Over time, wear and tear can degrade the stator's performance, leading to reduced efficiency, leaks, or complete pump failure.
Regular inspection of screw pump stators is essential to ensure optimal performance and prevent unexpected downtime. This guide provides a detailed step-by-step process for inspecting screw pump stators for wear, including visual checks, dimensional measurements, and performance assessments.
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1. Pre-Inspection Preparation
Before inspecting the stator, ensure the following steps are taken:
1.1. Safety Precautions
- Lockout/Tagout (LOTO): Ensure the pump is de-energized and isolated from power sources.
- Depressurization: Release any residual pressure in the pump and piping system.
- Fluid Handling: Drain and clean the pump to remove hazardous or corrosive fluids.
- PPE (Personal Protective Equipment): Wear gloves, safety glasses, and appropriate protective clothing.
1.2. Tools and Equipment Required
- Measuring tools: Calipers, micrometers, depth gauges, and profile gauges.
- Inspection light or borescope for internal examination.
- Surface finish comparator to check for roughness.
- Elastomer hardness tester (Shore durometer).
- Cleaning supplies: Solvents, rags, and brushes.
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2. Removal of the Stator
1. Disassemble the pump housing following the manufacturer’s guidelines.
2. Extract the stator carefully to avoid damaging the elastomeric lining.
3. Clean the stator thoroughly to remove debris, sludge, or residual fluids.
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3. Visual Inspection
A visual inspection is the first step in identifying obvious signs of wear or damage.
3.1. External Inspection
- Check for cracks, tears, or swelling in the elastomer.
- Look for blistering or delamination, which may indicate chemical degradation.
- Inspect for abrasion marks caused by solids in the pumped fluid.
3.2. Internal Inspection
- Use a bright light or borescope to examine the internal helical cavity.
- Look for grooves, scoring, or uneven wear patterns caused by rotor interaction.
- Check for hardening or softening of the elastomer, which affects sealing efficiency.
3.3. Common Wear Patterns
- Uniform wear: Indicates normal aging and gradual material loss.
- Localized wear: Suggests misalignment, excessive pressure, or rotor imbalance.
- Chipping or tearing: May be due to cavitation or abrasive particles.
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4. Dimensional Inspection
Accurate dimensional measurements help determine if the stator is within acceptable tolerances.
4.1. Measuring Stator Bore Diameter
- Use a caliper or bore gauge to measure the internal diameter at multiple points.
- Compare measurements with the original specifications.
- Excessive wear (>5% deviation) typically requires stator replacement.
4.2. Checking Helical Profile
- Use a profile gauge to compare the stator’s helical shape against a new one.
- Deviations in the pitch or depth indicate wear affecting pump efficiency.
4.3. Elastomer Thickness Measurement
- Measure the remaining elastomer thickness using a micrometer.
- If the thickness is below the minimum recommended value, the stator should be replaced.
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5. Hardness Testing
Elastomer hardness affects sealing and wear resistance.
- Use a Shore durometer (Type A for softer elastomers, Type D for harder ones).
- Compare readings with the original hardness value.
- Significant softening (>10 Shore points) suggests chemical attack or thermal degradation.
- Hardening may indicate aging or excessive heat exposure.
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6. Performance Testing (Optional)
If the pump is reassembled after inspection, monitor:
- Flow rate reduction (indicates internal wear).
- Pressure fluctuations (suggest sealing issues).
- Unusual noise or vibration (may indicate misalignment).
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7. Root Cause Analysis of Wear
Understanding why wear occurred helps prevent future failures.
7.1. Common Causes of Stator Wear
- Abrasive particles in the fluid (install filters if necessary).
- Chemical incompatibility (verify elastomer material suitability).
- Excessive temperature (check cooling systems and operating conditions).
- Dry running (ensure proper lubrication and fluid presence).
- Misalignment or rotor imbalance (verify pump assembly and alignment).
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8. Decision-Making: Repair or Replace?
- Minor wear (smooth, uniform, within tolerances): Continue monitoring.
- Moderate wear (localized damage, slight dimensional changes): Consider reconditioning if possible.
- Severe wear (cracks, deep grooves, loss of sealing ability): Replace the stator immediately.
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9. Preventive Maintenance Tips
- Regular inspections (schedule based on operating conditions).
- Proper material selection (match elastomer to fluid properties).
- Avoid dry running (install low-level sensors if needed).
- Monitor operating conditions (temperature, pressure, and flow rates).
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Conclusion
Inspecting screw pump stators for wear is a critical maintenance task that ensures long-term reliability and efficiency. By following a structured approach—visual checks, dimensional measurements, hardness testing, and performance monitoring—operators can detect wear early and take corrective action before failure occurs. Implementing preventive maintenance strategies further extends stator life and reduces downtime.
Regular inspections not only save costs but also optimize pump performance, ensuring smooth operations in demanding industrial applications.
Copyright ? Jiangsu Longjie Pump Manufacturing Co., Ltd.
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