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By: Brent Condrey, Lead CBM Analyst


During an Electrical Infrared (IR) scan at a health treatment facility, the breaker for a fan assembly was noted as having a much higher difference in temperature (Delta-T). This led to my investigations of:

  • Why is the breaker so hot?
  • Is it an electrical problem or a mechanical problem

This particular fan is used to circulate exhaust air throughout the “B-Wing” of the facility, thus creating a constant intake of fresh air to the facility via draft vents. Fresh air CFM requirements are critical in maintaining compliance with regulatory code. If this machine suffers a functional failure, it is unlikely to cause immediate diversion of any departments; however, regulatory compliance will cease.

Figure 1: Fan Assembly

Summary of Action

The first thing I decided to do during my investigation was to perform additional vibration readings on the bearings of the fan. This is a very large fan and, unfortunately, the only accessible bearing was the inboard fan bearing (a sleeve bearing). The outboard fan bearing was non-accessible and inside a confined space.

However, there was a small hole, 3/4 inch diameter, in the housing of the fan towards the outboard end of the fan assembly that allowed me to see the outboard bearing. Figure 2 shows a thermal image of the outboard bearing taken through the hole in the fan housing. This was a great help in determining the cause of the issue because I was able to see the type of bearing. It was a large DODGE Double-Interlock Tapered Roller Bearing and I noted it also looked dry around the seal area. This led me to believe it was a lubrication issue.


Figure 2: Outboard Bearing

The inboard fan bearing (Figure 3) is a different type of bearing. It is a sleeve bearing and is the only location where I could obtain vibration readings for the entire fan unit. Vibration readings were taken from the inboard fan bearing before any corrective actions were performed (Figure 4).

Figure 3: Inboard Bearing Location

Figure 4: Inboard Bearing Vibration Readings, Pre-Corrective Action

The infrared image in Figure 5 is of the EX-19 breaker inside panel 9200-DP-RPC before any corrective actions were performed.

Figure 5: Breaker Panel, Pre-Corrective Action

Plan of Action

The fan was locked out, confined space permits were issued, and the lubrication technician entered the area of the fan outboard roller bearing. He purged the bearing using the supplied procedure and filled it using white lithium grease. The bearing required almost a full tube of grease; the bearing was completely empty of lubrication and needed it severely. The unit was then unlocked and the quality check process begun.

Vibration readings were taken again after corrective actions (Figure 6). The vibration amplitude was reduced in half and a major reduction in “noise floor” energy was also noticed.


Figure 6: Inboard Bearing Vibration Readings, Post-Corrective Action

Next it was time to see if the associated electrical breaker was reading less of a current draw from the fan. Figure 7 shows the infrared findings of the breaker after running for at least an hour; less than a 1 degree Delta-T currently exists.

Figure 7: Breaker Panel, Post-Corrective Action


Using multiple technologies in any Predictive Maintenance Program allows the user to find more faults with more certainty. Had I not noticed the electrical high amp draw using infrared, I might have thought everything was fine with the fan bearings due to no alarms being exceeded. However, it turns out there was an obvious lubrication problem.

Figure 8 shows an overall vibration amplitude trend from the fan assembly’s inboard fan bearing vibration data. The lowest points in the trend graph show were the vibration amplitudes bottom out as a result of lubrication activities over the last year. This vibration data could also be used to demonstrate evidence of correct lubrication frequencies – or to set optimal lubrication frequencies if the data indicated that an improper frequency was being used.

Figure 8: Fan Inboard Bearing Data














Contributed by Jon Thebner, Lead Analyst

Problem Summary

The SEM transfer blower at a customer facility was plagued with high vibration throughout the history of the asset. This high vibration was predominantly in the radial direction of the outboard end of the blower. However, each data collection point showed high vibration levels regardless of axis.
The vibration spectrums commonly illustrated high amplitudes at 1X, 2X, 4X, and 6X blower running speed with varying axes (Figure 1). The identifiable frequencies remained dominant throughout the viewable history.
Table 1 shows common causes of elevated vibration at 1X, 2X, and 4X running speeds. The high amplitude frequency of 6X running speed is not associated with any type of forcing frequency in this equipment and therefore is considered to be a harmonic (multiple) of running speed vibration.

Common Causes of Vibration

Summary of Action

Advanced vibration analysis was performed on the blower and supporting base structure to determine the root cause of the elevated vibration levels that were affecting this equipment.

Bump Testing

A bump test was performed to determine the natural frequencies of the base structure and ensure that these frequencies were not within 10% of any forcing frequencies. Utilizing a soft impact tip on a modally tuned hammer, ten (10) different spectrums were collected and stored from various points across the base/structure.
Bump test results showed a common natural frequency of 7012 CPM from several of the points collected, along with a lower amplitude frequency of 3080 CPM (Figure 2). Typical operating speed of this blower is 2790 CPM. The first of the two (2) natural frequencies shown at 3080 CPM is 10.4% above the operating speed of the blower. The second (higher amplitude) frequency of 7012.5 CPM is 25.7% higher than the second multiple of running speed and 16.2% lower than the third multiple.
Operating Deflection Shape Analysis 2790 CPM (1X running speed) was used as the specified frequency during this test. A total of 79 points were collected in reference to one (1) point on the base and blower. A second set of data included an additional 25 collection points in reference to a single point on the blower. (See Figure 3 for data collection points.)
The results of the ODS animation showed a significant amount of movement in the base/structure as suspected. Figure 4 shows snapshots of the ODS analysis images. The different color shading indicates the movement captured at two (2) different time intervals.
A wagging motion was also identified at the outboard end of the blower. With this particular identified, eccentric or imbalanced sheaves were suspected as the root cause of the excessive vibration at 1X running speed. However, the sheaves were replaced during the winter outage and resulted in only a minimal change in the vibration levels across the equipment.

To view the ODS animation videos, please visit the following links:



Free Maintenance & Reliability Seminars

October 2, 2013

JOIN US FOR FREE SEMINARS IN ATLANTA, GA AND CHATTANOOGA, TN  1-Day Maintenance & Reliability Seminar With today’s economic conditions, can you afford NOT to maximize your Maintenance and Reliability efforts? Vibration Analysis, Precision Laser Alignment, Ultrasound, Motor Testing can achieve wonders in maximizing your uptime and lowering your costs of operation. Come and learn […]

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Vibration Analysis Discovers Flaw in System Design

September 20, 2013

By: Will Segraves, Lead Analyst   Synopsis The three (3) assets in question in an industrial manufacturing facility are horizontal C-face mounted, 15 horsepower, 1,800 RPM motors operated on a variable frequency drive at 1,595 RPM. The motors have 309 ball bearings in the Drive End (DE) and 206 ball bearings in the Opposite Drive […]

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Subsurface Fatigue Can Lead to Bearing Failure

September 11, 2013

A combination of technologies can alert to the early signs of failure The health of bearings is integral to the overall health of machines and to the overall health of a plant. Bearings can be seen as the “sacrificial lambs” of a rotating machine. For many machines, their relationship to bearings is much like that […]

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PdM Strategies For Compressed Air System Efficiency

September 4, 2013

  Compressed air systems are not inexpensive, and operating them can be costly, if routine monitoring isn’t done. Which predictive maintenance technologies or strategies should be used for air leaks, pumps, lubrication, or any other aspect of the system, and how will they help to improve efficiency and avoid costly failures? Here is a short […]

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Marley Model 27T Cooling Tower Fans

July 9, 2013

Equipment Information Marley Model 27T Cooling Tower Fan: •     192” fan with 5 blades, turning approximately 227 CPM •     7.71/1 ratio Geareducer •     AC Induction Motor: 4 pole, 60 HP, 364TS Frame •     Driveshaft/hubs: Marley Series 175 Twin-Flex driveshaft Technologies Applied •     Vibration – Monthly •     Motor Circuit Analysis (MCA) Offline/Online – Trimester •     Infrared […]

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Defect Elimination Success Story – Blend Tank Agitator

July 1, 2013

By: Leonard Kreiner, Vibration Analyst Equipment Information   Gearbox:   Lightnin, 72-C-3 Motor:      Toshiba, 3 HP, 1755 RPM, 182T Frame       Reported Defect   Problem Statement: There is looseness in the vibration spectrum. Examination of the coupling reveals that the coupling is cocked on the shaft. Recommendation: Check coupling for signs of wear, such […]

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Asset Failure Investigation Report – Cooling Tower Fan Gearbox

June 24, 2013

By: Leonard Kreiner, Vibration Analyst, and Chris Chasteen, Oil Analyst Equipment Details Gearbox:   2700 Series Marley Motor:      Louis Allis, 60 HP, 1775 RPM, 364T Frame           Failure Summary On Wednesday, May12, 2010, a work order was issued to troubleshoot why the input shaft of the cooling tower would not turn. After […]

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Multi-Technology Fault Identification

May 15, 2013

By: Reggie Fett, MCA/IR Analyst Industry: Food and Beverage Technology: On-line MCA (Initially) Component: Motor Part: Electrical Connections Time Context Tuesday, April 16, 2013 Process Information This asset is a pump used to pump water for the milling process and cannot be shut down for more than 3 hours during the milling process. Shutting down […]

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