Single Reduction versus Double Reduction Gearbox Reliability
Single Reduction versus Double Reduction Gearbox Reliability
(OP)
I attempted to do a search for my question and was not able to find any relevant threads. I apologize if I missed any.
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?
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?
Johnny Pellin
Talk To Other Members
RE: Single Reduction versus Double Reduction Gearbox Reliability
You should talk to the gearbox mfgr.
Mike Halloran
Pembroke Pines, FL, USA
RE: Single Reduction versus Double Reduction Gearbox Reliability
Johnny Pellin
RE: Single Reduction versus Double Reduction Gearbox Reliability
Just as a frame of reference, do you bother to keep local spares of any sort for the current 50 gearboxes?
Are there local external stocks for immediate delivery, or does someone have to restart an old factory to make parts for you?
I.e., what are your expectations re failure and serviceability?
I don't personally care, so you don't need to reveal anything here, but that's the sort of thing I'd be thinking about, were I in your position.
Mike Halloran
Pembroke Pines, FL, USA
RE: Single Reduction versus Double Reduction Gearbox Reliability
They may have a 'cooling towers inc' part number shown on the BOM, but I'd bet they're made by one of the few specialists out there.
If you're near a tower, go look at a physical gearbox and call the company on the name plate and ask them directly.
RE: Single Reduction versus Double Reduction Gearbox Reliability
RE: Single Reduction versus Double Reduction Gearbox Reliability
For a time I worked for a company that offered "predictive maintenance" services and had a bunch of commercial customers. We measured vibration on equipment bearings, did oil analysis, and a bunch of other stuff
My recollection was cooling tower gearbox failures most often resulted from gross lubricant water contamination, maybe exacerbated by infrequent oil changes.
RE: Single Reduction versus Double Reduction Gearbox Reliability
RE: Single Reduction versus Double Reduction Gearbox Reliability
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.
RE: Single Reduction versus Double Reduction Gearbox Reliability
The MTBF of any gear drive system will be determined by numerous factors, including component manufacturing/material quality, operating conditions, service/maintenance procedures, etc. All other things being equal, a gear drive having more components will have a statistically lower system reliability rate.
RE: Single Reduction versus Double Reduction Gearbox Reliability
A hypoid gear is a style of spiral bevel gear whose main variance is that the mating gears' axes do not intersect. The hypoid gear is offset from the gear center, allowing unique configurations and a large diameter shaft. The teeth on a hypoid gear are helical, and the pitch surface is best described as a hyperboloid.
Showing my age here but I've worked on cars, Hot Rods, and even a Pro-Street Dragster since the mid 70's when you could work on your car in the garage.
RE: Single Reduction versus Double Reduction Gearbox Reliability
The tradeoff is that they are less efficient. So newer cars are actually migrating toward spiral bevel final drives. Trucks are holding on to hypoid axles because they need the higher torque transmission.
RE: Single Reduction versus Double Reduction Gearbox Reliability
Technically, I don't believe hypoids are considered true bevel gears, like straight/zerol/spiral bevels. Don't know about face gears though.