The gearbox is one of the key components of the equipment in medium and large cooling towers. It is the most expensive component in many cases, and the one exposed to the hardest working conditions. Therefore, it is important to carry out appropriate maintenance work following the manufacturer’s instructions.
Correct lubrication prevents metal-to-metal contact between teeth and bearings, reducing friction losses and dissipating the heat generated, as well as preventing corrosion.
Greasing is done by bubbling as standard. Gears and bearings are greased by immersion in the oil bath. Although normally the upper bearings and labyrinth seal are greased, in some cases their lubrication is also ensured by oil circulation through an integral pump driven by one of the gearbox shafts.
It is important to check the oil level weekly using the dipstick with the gear unit stopped. The first oil change should be made after 100 hours, never after 800 hours of operation. Subsequently, the oil should be renewed after 4000 to 8000 hours, never after 18 months of operation. The oil must be drained while the gearbox is still hot, by removing the filler plug. Oil samples can also be taken periodically for subsequent analysis, thus checking the condition of the oil, deterioration, wear particles, possible water contamination, etc. In this case, it is advisable to install a valve for sampling. This prior analysis will facilitate maintenance tasks, which may shorten or lengthen the intervention times, and will help us to get a better control of the gearbox, anticipating possible breakdowns, improving its performance and increasing its operating life. Only the type of oil and viscosity index indicated on the gearbox plate should be used.
On the other hand, the grease must contain EP additives and NLGI-Grade 3 consistency. It is important to add grease every 800 hours of operation at all greasing points.
The dipstick plug normally has an air hole to prevent any overpressure. The ventilation hole must be checked regularly to ensure that it is not blocked.
If the unit does not work continuously, it is recommended that a backstop be installed to prevent the fan from rotating in the opposite direction due to eddy currents. The backstop is integrated in the gear unit and is lubricated with the same oil bath as the gear unit. It does not require any additional maintenance except for inspection every two years.