Companies that operate high capacity production plants – like those in the chemical process and power industries – require cooling towers with large amounts of heat rejection capacity.

Gearboxes are used as speed reducers to slow the rotational speed from the incoming motor to the outgoing fan of a cooling tower. Without this technology, cooling tower motors would be massive to directly handle the torque required by the fan. So massive, in fact, they would be too expensive and impractical. The speed reduction from the gearbox acts as a torque multiplier, however, keeping the motor a reasonable size and the overall mechanical system more cost-effective.

In a white paper, SPX Cooling Technologies explains how the speed reduction from gearboxes also optimizes the performance of the cooling tower fan. As fan diameters increase, the fan speed must decrease to maintain acceptable sound and vibration levels and to ensure the structural integrity of the fan itself. Improper gearbox sizing as it relates to the motor and fan can result in excessive vibration, loud operation and structural damage to the tower. 

In large cooling tower applications, the fan typically operates at a speed between 100 and 200 rpm. The most common motor speed is 1,800 rpm, which requires the average gearbox to reduce motor speed by approximately nine to 18 times to achieve the desired fan speed. The exact combination of this gearbox ratio, fan blade design and fan pitch contributes to the specific performance and energy efficiency of the cooling tower.