Cooling towers are prone to the typical causes of rotating machine failure such as misalignment, but also face a range of specific environmental challenges, including high or gusting wind speeds, dust, sand and, in coastal locations, high concentrations of salt.

In the 1990s, for example, vibration and accelerated wear caused a fan blade to shear off a cooling tower in Pennsylvania, resulting in significant imbalance.  Fan, motor and gearbox were ripped from their support, and the entire assembly fell into a basin below the tower deck, taking the walkway that supported the fan system with it. Inspectors of the catastrophic failure in Pennsylvania identified that, although vibration switches were used, they had failed to function due to ingress of moisture.

Fans, motors and gearboxes in cooling towers are all subject to extreme conditions. For example, because cooling towers are often sited in exposed locations, high wind speeds and downdrafts can affect fan operation.  Proximity to the sea will bring a concentration of salt in the atmosphere, while any nearby plant will cause dust and particulates to enter the system.  All of these conditions will cause corrosion and damage to motor and fan units. Similarly, the position of the gearboxes beneath the fan units means that they are continuously exposed to the flow of water as it is blown down each cell.

This means that vibration monitoring equipment must not only be supplied but correctly specified to resist corrosion. Suppliers can now choose exceptionally robust industrial accelerometers with high IP (ingress protection) ratings to minimise such failure. With knowledge of the best sensor and detection technologies available today and how these can best be used, maintenance engineers can not only prevent failure but also significantly maximize machine uptime.