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Although the primary role of a cooling tower’s gearbox is to reduce the speed of the driver (usually an electric motor) to an efficient fan speed, there are several other important requirements for proper cooling tower operation.
A gearbox must provide primary support for the fan’s weight and rotational forces, withstand the shock loads imposed at start-up and during subsequent speed changes, and also limit power usage and noise.
5 things to consider when you need a cooling tower gearbox
These functions make the gearbox the heart of the cooling tower; it must be a steadfast solution to ensure reliable performance. Many manufacturers of mechanical equipment provide acceptable “geared speed reducers,” designed for more forgiving commercial applications; however, these units are often unprepared for the work of cooling tower service. Add to this the corrosive effects of operation within an exceedingly humid environment, and the life expectancy of these commercial speed reducers often suffer.
So how do you know which gearbox is right for your service conditions, maintenance plan and project timeline? And what should you consider when you’re deciding on a gearbox manufacturer? Here are five factors to guide your decision-making process.
1. Oil change intervals
Although oil changes are routine maintenance, your gearbox’s oil change can end up costing a surprising amount of time and money. This is why you should consider the frequency of necessary oil changes when choosing the best gearbox for your cooling tower(s).
For many double reduction gearboxes, the original oil should be replaced after just 500 hours or 4 weeks of operation. After the first change, intervals of 2 or 3 months may be required for a very moist atmosphere. On the other hand, Marley® Geareducer® double reduction gearboxes only require operators to change the oil every 3,000 hours, which can save up to $1,419 in annual oil change costs.
Other key gearbox design considerations when looking at oil change requirements include:
- Larger oil pathways,
- Quality oil seals or oil seal upgrades, and
- Value add-ons, such as low-level oil indicator switches and anti-reversing devices.
2. Vibration and noise
In some cases, vibration can cause considerable damage to gearboxes and surrounding components in just a few years. For example, after only a few years of operation, a plant in North Carolina noticed considerable vibration effects and gear damage to their gearboxes.
The facility tried upgrading all 10 cells to the larger version of gearboxes from the same manufacturer – and started using a special lubricant with auxiliary oil coolers and air purge lines – but the issues persisted, while lifecycle costs began to stack up. After that, the plant decided to install Marley M Series Geareducers, which were an easy drop-in replacement for the other gearboxes. The Marley M Series Geareducer solution reduced vibration and provided the facility with a longer warranty on the equipment. Furthermore, severe vibration often results in excessive noise in a gearbox, so gearboxes should be verified for gear sound by third party test results. Ask your OEM about their sound data before deciding on a gearbox solution for your cooling towers.
3. Bearing life expectancy
Bearings are a vital part of every gearbox, and the bearings used in each manufacturer’s gearbox model should be treated as such when integrated into the design. While many OEMs use single-row interstage shaft bearings, others use double-row bearings because of their clear performance advantages and longer life. For example, all Marley double-row interstage bearings have 100,000 hours minimum L10A service life, yielding as much as 3x the bearing life of single-row bearings in other gearboxes.[1]
4. Lifecycle and remanufacture/repair options
Guarantees on service life are difficult to provide when service conditions vary so greatly from facility to facility, let alone tower to tower, but operators can determine a predictable lifecycle when you consider available warranty and service history.
Design and engineering considerations – like housing durability, bearing rating, gear quality and additional features like cooling fins – along with real-world service data, are what lead manufacturers to offer warranties on their gearboxes. Operators should consider the equipment warranty as a sign of an OEM’s product experience and development techniques. When it comes to gearboxes, a new Marley Geareducer is delivered with a five-year warranty while other manufacturers offer 3 years or less.
5 things to consider when you need a cooling tower gearbox
And when the time comes for your gearbox to be taken out of service, it is advantageous for an operation to know their remanufacturing or repair options for their equipment. If you need major repairs or would prefer to purchase a new Geareducer, Marley has several options to get you up and running with new or good-as-new gearboxes, each of which comes with a best-in-class warranty to guarantee the highest Marley quality.
5. Single source provider
When buying equipment for your facility, it is always easier on the backend to limit vendors and suppliers as much as possible. Whether you need a new gearbox, cooling tower fill media or to expand heat rejection capacity and build completely new towers, manufacturers like SPX Cooling can assist you and your team with all your cooling tower needs.
SPX Cooling Tech – the company that manufactures Marley Geareducer gearboxes – designs components uniquely for cooling tower service and, since SPX/Marley warrants both the cooling tower part and the thermal performance of the cooling towers on which they operate, the development, design, and manufacturing of every cooling tower part is taken very seriously. This has resulted in an unequalled history of reliable operation, providing cooling tower parts for over 100 years and gearboxes in more than 100,000 towers around the world.
What else should you consider?
When it comes to field-erected cooling towers and their components, the Marley team in Houston can help with everything from routine maintenance to emergency repairs, and can provide new, remanufactured or repaired gearboxes when you need one most. To get started, contact the Marley Parts & Service team today.
1 Based on current Timken bearing rating method for Marley Series 4000 vs. Amarillo 1712
