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Fix the root cause, not the symptom.

How pulley misalignment led to discovery of a motor base crack

By:

SKYLER

The Challenge

Effective predictive maintenance requires identifying root causes, not just treating symptoms. Superficial fixes lead to recurring failures and unnecessary downtime. A truly intelligent monitoring system must guide customers to the underlying problem.

fix-the-root-cause

The Situation

Skyler’s monitoring system detected concerning vibration trends on an industrial belt-driven fan. Velocity vibration level steadily increased from 0.2 IPS to over 1 IPS within one month-a pattern consistent with pulley misalignment.

What made this case unusual was the timing. Typically, misalignment appears immediately after maintenance when pulleys aren’t properly realigned. However, this misalignment developed gradually over time, suggesting a deeper issue at play. This atypical progression prompted Skyler’s team to investigate beyond the obvious diagnosis.

What We Detected

Vibration Evidence

  • Velocity RMS Trends: Continuously
    increasing from 0.2 IPS to over 1 IPS
    in just one month
  • Component: Motor Drive End (DE)
  • Motor Speed: 1,800 RPM

Diagnostic Pattern

The vibration signature revealed two key indicators of pulley misalignment:

  1. Elevated fan shaft speed peak amplitude on motor sensors – higher than the actual motor shaft speed peak.
  2. Progressive increase in fan shaft speed peak amplitude over time

Potential Consequences

If left unaddressed, this misalignment would cause:

  • Accelerated motor and fan bearing degradation
  • Premature belt and sheave wear
  • Shaft bending stress
  • Reduced fan output due to decreased torque capacity and higher belt slip

Velocity Trend Analysis

Component:

Motor DE

Speed:

1800 RPM

Pattern:

Continuous increase in the velocity trends up to 1 IPS.

fix-the-root-cause_chart_1

Spectrum Analysis

Component:

Motor DE

Speed:

1800 RPM

Pattern:

Predominant increase at the fan shaft speed peak.

fix-the-root-cause_chart_2_2x

Our Recommendations

  • 1
    Immediate Check:

    Inspect pulley alignment, belt Examine motor base for condition, and sheave wear.
  • 2
    Deeper Investigation:

    Examine motor base for condition, and sheave wear. structural looseness,  hardware, or cracks.

    *The second recommendation proved to be critical.

On-Site Findings

The customer’s reliability team scheduled an inspection during a planned outage. What they discovered validated Skyler’s deeper investigation approach:

Multiple alignment attempts failed:
Despite repeated efforts, pulleys could not be aligned to acceptable tolerances.

 

The critical clue:
Each time belts were properly tensioned, the misalignment immediately reappeared

Root cause identified:
Thorough inspection revealed a hairline crack underneath the motor base –
difficult to spot but causing the recurring alignment issues

The Result?

$20,500 in total savings.

Action Taken:

  • Motor base plate replaced
  • Pulleys successfully aligned after 
 base replacement

Root Cause Confirmed:

Belt tensioning caused the cracked base to flex and strain, making proper alignment impossible. This was a textbook case where treating the symptom (misalignment) would have led to repeated failures. Only addressing the root cause (cracked base) provided a permanent solution.

Value Delivered:

  • Catastrophic failure avoided: Prevented potential motor failure and unplanned downtime
  • Cost savings: Minimum $18,000 in avoided unplanned downtime
  • Equipment savings: $2,500 in motor replacement costs avoided
  • Operational continuity: Issue resolved during planned maintenance window

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