By Brandon, Rees

Regional Sales Director

Cooling Tower DEPOT, Inc.

When it comes to cooling tower mechanicals we can be assured of one thing... Your gear drive can make or break the overall tower performance. Spend just a little time in the field and you will realize that the gear drive can present issues, that depending who you ask, can have various solutions. Let’s take a moment to review some of the most common issues and ways to prevent them from starting in the first place.

Common gear drive operations
The operation of your gear drive on the surface would seem to be pretty straight forward. However, there are some things to keep in mind to ensure longevity out of your gear drive. A drive can be operated in three different ways

• With a single speed motor


• With a two speed motor


• With a Variable Frequency Drive

When it comes to single speed motor operation one of the main things that we should be concerned with is damage to the gear teeth. The main cause of damage to the gear teeth is through large torque spikes. As energy is transferred from the motor through the driveshaft to the gear drive torque is displaced and absorbed, mainly by the internals of the gear drive. To prevent large torque spikes remember the following. Always use a NEMA Design B motor to limit starting torque. Never use a “Y Delta” starter, as these can produce large torque spikes. Always make sure that the fan is not “wind milling” in reverse direction prior to motor start up. If icing is not an issue in your area you may want to consider a non-reverse option to be added to your gear drive. For just a little more cost, take the worry out of the equation.

Two speed motor operation can also present gear teeth damage issues. Remember to make sure that the gear drive has an adequate torque rating at both motor speeds. Always use a time delay when changing from the low speed to the high speed. Also don’t forget about the pesky “wind milling” effect. (Just go ahead and get the non-reverse adder)
Now Variable Frequency Drives (VFD) need to be looked at a little more closely. Yes they can save money in power consumption over time. They also prolong the life of the gear drive by mitigating some of the harsh wear and tear of single or two speed motors, but if not set up correctly from the beginning, VFD’s, can have the opposite effect. So please remember to lockout speeds that excite the systems natural frequencies (+or - 5 Hz). Both critical speed and blade pass frequencies should be taken into account. If you don’t know what these speeds are for your tower call Cooling Tower Depot Inc. and we can help. Keep in mind that the deceleration rate of the gear drive should be greater than the natural coast-down time. Do not operate above the gear drive nameplate speed. Lastly, do not operate below the minimum speed allowed by the gear manufacture. For example, Amarillo Gear Company’s minimum speed is 450 RPM. If you are using a single reduction gear drive, you may want to consider the low speed option. This ensures that the vertical upper bearing is properly lubricated at all times alleviating the need for mechanical or electrical oil pumps.

Common gear drive maintenance practices
Lubrication seems to be the largest issue related to gear drive failures. What can we do to ensure that our gear drives are properly lubricated at all times? Well, we can start by using some best practices for maintenance and inspections.
Monthly Inspections would suggest that we drain water off the bottom of the oil sump or filter oil through a water/ particulate filter.
Quarterly Inspections would suggest that we take an oil sample and have it analyzed. Collect vibration data, check function of cutout switches, and check the non-reverse device.

Semi Annual Inspections: according the operating and maintenance manual provided by Amarillo Gear Company; it is recommended that all oil be changed at 2,500 hours or every 6 months regardless if mineral or synthetic. Don’t have an O&M manual for your gear drive?
Don’t worry just head to the Depot Digital Library and pick up your O&M Manual for your gear drive!

Here are some tips to remember as you analyze your gear drive oil

• Selecting and reading your oil sample analysis can be an art in and of itself. Make sure to request the Karl Fisher analysis for accurate water content. This helps to paint the picture you’re looking for. Water content should be below .01%. Every analysis should include viscosity and a total acid number (TAN). An increase in both the viscosity and TAN indicates oxidation and oil should be changed immediately. If you see a high particulate count this is indicative that damage has already occurred to the internals of the gear drive. If this happens please contact Cooling Tower Depot, and we can make sure that your drive is repaired properly and is back in service in no time.


• When it comes to selecting the right oil for your drive there are several brands out there that say they are the best. If you have one that is working for you, then keep using it! Just make sure that it follows these manufacturer recommended guidelines. Extreme Pressure or “EP” additives are not recommended. They have be proven to cause damage to the internal lining of the gear case over time as well as bearing life reduction at high operating temperatures. Use 220 viscosity oil (either mineral or synthetic). If using a mineral oil please note that the minimum operating temperature is 20°F and the maximum operating temperature is 180°F. For synthetic oils the minimum operating temperature is also at 20°F and the maximum should be at 220°F. Synthetic oils generally last longer and handle higher temperatures better. For a little more in oil cost you can help extend the overall life of your drive. Next time you order a new drive ask us to ship it with Mobile SHC630 synthetic oil! If you are in a colder climate and oil temperatures fall below 20°F, ask us about adding an oil heater to your next gear drive order.


• If your tower runs in cycles you are more prone to have water in the gear drive oil than those that run continually. For example power plants vs. refining applications. As the gear drive runs a small amount of pressure can build up inside the drive (around 5-10 PSI). When the drive cools it tends to pull in air, and water along with that air, back into the unit. Keeping with the above best maintenance practices will keep your gear driving running problem free for years to come.

Be sure that your drive keeps operating the way you want it to
Check the Seals: Now that you have selected the right motor operation, and the right oil how can we keep the drive operating the way we want it to? One way is to check the seals. The standard Nitrle Rubber seals on the input shaft of your gear drive will generally last 3-5 years (under continuous operation). They can easily be changed in the field, and will help ensure proper oil levels at all times. Ask us how to upgrade your seals to Viton, and get the most life out of your seals!
Vibration Monitoring: Another way to ensure a long lasting gear drive is vibration monitoring. Vibration switches work well in preventing a catastrophic failure. We recommend a vibration switch that is mounted outside the fan stack to avoid corrosion of the internal mechanism. The plenum area is a harsh and corrosive environment, and locating switches outside the stack make it much easier to access for resetting and maintenance... You won’t have to get a confined space permit! For the best in vibration monitoring consider using a vibration transducer. The transducer gives a much more accurate reading and can help with diagnostics and the prevention of a catastrophic failure. Ask us to have your next gear drive drilled and tapped for a vibration transducer!

Experience and quality come together
When it comes to gear drives, Cooling Tower Depot Inc. understands that our customers want quality and affordability, which is why we have partnered with Amarillo Gear Company. AGC has been in business since 1917 and has been the premiere cooling tower gear drive manufacturer since 1964. In 2007 Cooling Tower Depot Inc. invested close to $1,000,000 in our in-stock Amarillo Gear Drive units. If you should ever have a failure and need an emergency replacement we have an option for you. We stock the world’s largest supply of Amarillo Gear Drives, including the most common models and ratios. We are constantly replenishing our inventory, and with more than half of the cooling tower installations in the US using AGC gear drives rest assured that Cooling Tower Depot has you covered!
If you have a new tower project that has a short lead time we can use one of our in-stock units to help lower the overall lead time as well. Make sure to get a quote from your Cooling Tower Depot Inc. sales professional ahead of time and know that CTD will be there when you need us.
Have a Marley Gear drive? No problem! Cooling Tower Depot Inc. also stocks refurbished Marley units as well as the Amarillo Gear Company “A” Series (drop in replacement for Marley Gear Drives).

Night or day, perfect weather or hurricane conditions, Cooling Tower Depot Inc. is equipped to handle any and all of your cooling tower needs. We are the DEPOT of all cooling towers!

Have any questions?

I have been working specifically with gear box operations for many years. Feel free to contact me at my office:
Brandon Rees
Regional Sales Director
Cooling Tower Depot Inc.
281-542-1234 ext. 3
brees@ctdinc.com

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