Single Reduction versus Double Reduction Gearbox Reliability

We are in the process of designing a replacement cooling tower. It is expected to have 6 fans, 18 feet in diameter, driven by 150 HP motors. The cooling tower manufacturer is proposing that we use single reduction gearboxes. All of our existing cooling towers (6 towers with 50 fans) use double reduction gearboxes. The project manager is asking for justification to spend more to get double reduction gearboxes. For clarity, we are talking about right angle gearboxes that have input speeds of 1800 rpm and output speeds in the range of 150 to 190 rpm.

Should we expect to pay a penalty in reliability or service life by using single reduction gearboxes rather than double reduction?


In 30+ years of using many styles of single, and multiple stage boxes, straight, helical, bevel, spiral bevel I haven’t had any particular issues with any style.
It’s all in things like service factor and knowing what it needs to do.
The spiral bevel rear differential in my pick up has 429,000 miles on it with only oil changes for maintenance.
I’ve had planetary units radially explode in months because a sales men told my then boss they where just as good as the one we’ve been using since 1959.
We still manufacture the 1959 version basically and I overhaul about 40 units a year and it rare that we replace gears due to wear alone.
Most damage is from neglect and abuse.
If you are using the gearbox to support the fan blades I’d be looking more at the output bearings than the number of gear sets.

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