Original Date: 04/07/1997
Revision Date: 04/14/2003
Best Practice : Vibration Analysis
The previous base operation contract at Rock Island Arsenal (RIA) for all HVAC building operation, chiller operation, and preventive maintenance did not include vibration analysis. Mechanical failures of pumps and chillers were occurring randomly, and always at the worst possible time when the greatest interruption to operations would occur. The repairs required crisis management and, in some cases, long lead time parts were needed for the repair. Customers were generally without air conditioning during the hottest days, and the service desk would be overwhelmed with calls. The budget could not be maintained due to the unpredictable nature of the failures and the need for fast expensive repairs.
In 1996, RIA began using predictive maintenance techniques with in-house personnel. The first step was to identify which equipment was essential or critical. Vibration monitors are attached to the equipment, and the vibration signature is recorded when the equipment is new or after it has been repaired. The signatures are then recorded monthly and compared to the initial readings using Entek software from IRD International and the experience of the analyst. If the data indicates that a failure will occur, a prediction can be made as to when it will occur. This allows time to order parts, schedule the repair during the least interruptive period for operations, and avoid a failure. The confidence level in the equipment working when it is needed is significantly enhanced.
The application of preventive maintenance through vibration analysis is invaluable, but analysts and the software used can affect the conclusions. The experience of the analyst, the analyst’s training, and the proper application of the equipment are critical. Training and faith on the part of the maintenance personnel are also required to accept the results. Many times the vibration analysis will show a problem with an apparent perfectly-functioning unit. Experience at RIA has shown that when the vibration analysis indicated a problem, it really was a problem. One chiller that was working fine and had no indication of a problem was analyzed, and a problem was identified with a bearing on a shaft (Figure 2-4). When the unit was taken down for repair, it was determined that the bearing on the shaft was indeed faulty and would have caused a catastrophic failure if it had been left. A second and third chiller that were apparently working fine were found to exhibit signatures that indicated they would fail. The equipment manufacturer performed a vibration analysis, but concluded from the data that there was no problem. With RIA’s persistence, the manufacturer reluctantly agreed to disassemble the equipment. In the second chiller, the manufacturer found that a Bellville spring holding a bearing in place was improperly assembled. In the third chiller, seven bad bearings were found. The manufacturer then sent his personnel to RIA to learn how the analysis was being performed and to gain from the expertise developed at RIA. The cost for the 150 transducers that have been installed was $21,000. The cost for the monthly data collection and analysis is $800.
Mechanical failures can be virtually eliminated from equipment by using the vibration analysis techniques. Maintenance can be scheduled when it will not disrupt the operations. Repair parts can be ordered in advance of the maintenance action. The state of crisis management is eliminated, and proper budgeting and planning can be performed. Many times the problem can be identified far enough in advance to allow the repair to be performed following the air conditioning season.
Figure 2-4. Vibration Analysis
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