Main Causes of Gearbox Failure

The gearbox is a critical component of a cooling tower. Powered by an AC motor, the gearbox drives the large rotating fan blades that cool the water. Operating under variable load conditions, the gearbox is subject to excessive and prolonged stresses that cause degradation. Needless to say, degraded performance leads to system failure. And system failure leads to a whole host of trouble that affects your productivity, budget, and safety.


Vibration is a real problem for the gearbox. It is caused by imbalance, misaligned drive shafts, wear or excessive loading. High vibration levels can lead to gear tooth fracture, shaft deflection, galling and scaling, and plastic yielding.

Failure to Properly Maintain and Inspect Cooling Towers

This can lead not only to system failure but also to the incubation and spread of infectious, life-threatening diseases such as legionella.

Environmental Factors

Dust, dirt and humidity can cause bearing corrosion and gear tooth fracture, each of which significantly shortens the lifespan and effectiveness of a gearbox. Due to the difficulty of accessing them, cooling towers, and gearboxes in particular, are vulnerable to environmental factors because they are often not maintained and inspected as often as they should be.

Improper Lubrication

Improper lubrication is a common cause of gearbox failure. Usually, insufficient or interrupted lubrication schedules, oil film breakdown, shaft seal leaks, or foreign materials in the lubricant are responsible for lubrication problems. A gearbox that’s not lubricated properly may experience scaling and galling failures, excessively high temperatures leading to tooth surface damage, gear and bearing failures, and compressor drive failures.

Preventative Maintenance Mitigates Risk of Gearbox Failure

The best defense against unscheduled downtime and the potentially dangerous consequences of cooling tower system failure is a proactive, periodically scheduled preventative maintenance plan.

Effectively working to lengthen the lifespan of your gearbox and keep your cooling tower operational, a preventative mechanical maintenance plan includes:

Vibration Analysis

Periodically scheduled vibration analyses are a predictive measure to ensure the timely detection of potential problems. A vibration analysis is completed with a low frequency accelerometer and two monitors capable of detecting gear mesh frequencies, blade passage and bearing defect frequencies. A trained analyst reviews the data to detect if there are any undesirable mechanical forces creating problems in your gearbox that could lead to a failure.

Regular Lubrication and Oil Analysis

Proper lubrication requires using the right lubricant and the best method. Your cooling tower maintenance specialist will determine which is best for your equipment. In addition to periodically scheduled lubrication, your technician will conduct an oil analysis to uncover a concentration of particulate matter that may lead to problems.


Timely repair of cooling tower mechanicals is essential to avoid the high cost of total system failure, including lost productivity and higher costs associated with emergency service and expedited part orders. Your mechanical equipment is going to need repair at some point, there is no doubt. Planned repairs save you time, cost, and hassle. They can be scheduled to meet the needs of your business and your budget.

Remote Monitoring

Remote monitoring provides continuous data on machinery health and allows for the timely detection of issues before they lead to failure.

Partner With a Cooling Tower Professional

The gearbox is a critical mechanical component of a cooling tower that is subjected to the most wear and tear. As a result, it requires regular testing, maintenance and repair to keep it and your system operational. Difficult to access, and therefore a challenge to maintain, gearboxes often do not receive the attention they require.

Don’t wait for a catastrophe to occur. Partner with an experienced mechanical contractor with the cooling tower knowledge. Protect your assets and your business.

For cooling tower services, including maintenance plans and inspections, emergency services, and mechanical repairs, call Donnelly Mechanical (718) 886-1500.

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