FAQ

  1. What is the expected pump flow rate?
  2. What is the oil pressure expected for AGC parallel?
  3. Is there an oil or oil additive that could be used to extend the maintenance period to 4000 hours? This would allow the oil change to happen at the same time as the turbine maintenance.
  4. Other than a belt drive, is there an alternative gear that could be used to extend the maintenance intervals?
  5. What is the maximum surface temperature of a gear drive?
  6. During long term storage, should the gear drive be rotated by hand periodically?
  7. On a pump drive with spherical roller thrust bearing, why would the gear drive be difficult to turn by hand?
  8. What is the maximum vibration level for Amarillo Gear drives?
  9. What is the procedure for removing the rust preventative coating from exposed shafts?
  10. What are acceptable values for used oil analysis?
  11. Can the breather be installed inside the fan shroud?
  12. Can I replace my Brand X cooling tower gear drive with an Amarillo?
  13. Can I use Brand X oil in my fan drive?
  14. During cold weather operation, when are heaters and/or synthetic oil recommended?
  15. What modifications does Amarillo Gear Company recommend based on ambient temperatures around our cooling tower gear drives?
  16. What are the pros and cons of adding an oil filter to a gear drive?
  17. Describe how the oil filter system works on a double reduction fan drive?
  18. Why doesn’t Amarillo Gear recommend EP oils?
  19. Does my fan drive need a mechanical oil pump?
  20. What is the minimum oil level below the normal oil level for fan drives without oil pumps?
  21. Will “wind milling” damage my cooling tower fan drive?
  22. Does my gearbox need to be aligned? If so, what are the tolerances?
  23. What is a bearing’s “L10a” rated life?
  24. Where should I put a vibration sensor on the gearbox?
  25. What hardware and torque is used to install my fan drive in the tower?
  26. What is the Warranty policy for new vs renewed gearboxes?

What is the expected pump flow rate?

Answer: For Viking pump 23579: @400 RPM flow rate is 6 GPM, @1750 RPM flow rate is 33 GPM.

What is the oil pressure expected for AGC parallel?

Answer: As long as there is pressure during operation, gearbox should be receiving sufficient amount to maintain lubrication. At set up, 31 psi is expected. If pressure falls below that, could be rise for concern.

Is there an oil or oil additive that could be used to extend the maintenance period to 4000 hours? This would allow the oil change to happen at the same time as the turbine maintenance.

Answer: Amarillo Gear does not recommend the use of an additive.

  • Amarillo Gear does not encourage the extension of oil changes without a Comprehensive Monitoring Program.
  • Longer life could be achieved with a synthetic oil. Options are identified in the Fan Drive O&M
  • Monitor oil to determine optimal timeline for change
  • Once this timeline is determined, oil life COULD possibly be extended but will only know that by testing.

Other than a belt drive, is there an alternative gear that could be used to extend the maintenance intervals?

Answer: Amarillo could offer another gear (Double reduction gear) but this would require significant structural changes.

What is the maximum surface temperature of a gear drive?

Answer: There are many factors that affect the surface temperature of the gear drive. Examples of these are air velocity, air temperature, humidity, and radiant heating from exposure to sunlight. Because these variables are outside of our control, we do not set limits on the surface temperature of the gear drive.

The lubricant film strength is the most important factor for assuring the longest operational life of the gear drive. Proper film strength assures separation of metal surfaces and prevents premature wear. Since the film strength is determined by the oil temperature, it is the parameter that should be monitored during operation of the gear drive. The lubricant used in our gear drives is selected to provide adequate film strength at 200°F (93.3°C).

Again, many external factors can affect the oil temperature. There is no maximum value, only different solutions based on the actual operating oil temperature. For example, if the oil temperature is between 180°F (82.2°C) and 200°F (93.3°C), a mineral oil has adequate film strength, but it oxidizes at a faster rate. In this case, the oil must be changed more frequently. (Many users will not do this, so our O&M Manual cautiously recommends synthetic oil above 180°F (82.2°C).) At temperatures, above 200°F (93.3°C), we recommend using a synthetic product that provides greater film strength than a mineral oil. Only in extreme circumstances should the oil temperature reach or exceed 200°F (93.3°C).

During long term storage, should the gear drive be rotated by hand periodically?

Answer: The weight of internal components is small compared to the load capacity of the bearings, so “Brinelling” of the bearings is not a concern unless the gear is installed and has heavy components attached to the shafts. The only reason to rotate the shafts periodically is to distribute the oil on internal parts exposed to air to reduce oxidation and corrosion. Our long-term storage procedure requires filling fan drives completely with oil which dispenses with the need to rotate the shafts. On pump drives, it is recommended to rotate the shafts every month as stated on the nameplate.

On a pump drive with spherical roller thrust bearing, why would the gear drive be difficult to turn by hand?

Answer: The spherical roller bearings are spring loaded which increases the torque required to turn the shaft. In addition, the thrust bearing outer race can be knocked off-center during shipment, so the gear drive would be very hard to turn. The thrust bearing is self-aligning once it rotates with an applied load.

What is the maximum vibration level for Amarillo Gear drives?

Answer: The maximum value for lateral vibration is 0.3 in/sec (8 mm/sec) peak, filtered reading. This means that on a vibration spectrum, with frequency on the X-axis, none of the peaks should be above the 0.3 in/sec (8 mm/sec) level. Reference AGMA 6000 for more information.

What is the procedure for removing the rust preventative coating from exposed shafts?

Answer: Cortec VCI-358 is applied to exposed shafts prior to shipment. This product may be removed from the shafts using a cloth soaked in mineral spirits, alkaline cleaners, aliphatic solvents, or vapor degreasing solvents.

What are acceptable values for used oil analysis?

Answer: Typical acceptable values for continued use of a gear oil are:

Viscosity AGMA 4 – greater than 135 cSt and less than 165 cSt at 40°C
AGMA 5 – greater than 198 cSt and less than 242 cSt at 40°C
Water Content less than 400 ppm
Total Acid Number (TAN) less than 2.0
Wear Metals
  • Iron
  • Lead
  • Copper
  • Chromium
  • Aluminum
  • Tin
  • Silver
  • Silicon
  • less than 300 ppm
  • less than 75 ppm
  • less than 275 ppm
  • less than 30 ppm
  • less than 40 ppm
  • less than 30 ppm
  • less than 30 ppm
  • less than 60 ppm

In addition, if the viscosity increases 10% or more between samples and the TAN increases, the oil should be changed. This is an indication that the oil is oxidizing at a rapid rate.

Note: TAN is the amount of KOH required to neutralize one gram of oil and is a measure of the oxidation. This is sometimes called the neutralization number (NN). Another measure, the oxidation number, is a product specific value and is performed on an infrared spectrometer. The units for oxidation number are absorbance/cm. To use oxidation number, the oil manufacturer must specify the acceptance limits for the specific product. As an example, Mobil Gear 630 has an upper limit of 8.0.

Can the breather be installed inside the fan shroud?

Answer: Amarillo Gear does not recommend placing the breather inside the fan shroud. This placement could potentially draw humid air into the gear case and contribute to oil contamination. Ideally, the vent line should slope downward to the outside of the fan shroud with the breather at the lowest point. Piping that forms “traps” should be avoided to prevent the vent line from filling with oil or water and preventing the gear drive from breathing.

Can I replace my Brand X cooling tower gear drive with an Amarillo?

Answer: Yes. Amarillo Gear Drives are designed specifically for the demanding environment of cooling towers. Therefore, the drives may be physically larger than many of the “industrial” gear drives that have been adapted for use in cooling towers. Some tower modifications may be required to replace the existing gear drive with the Amarillo model. Some of the items that must be considered are: shaft sizes, location of the fan in the shroud, height of the input shaft from the base, required coupling length, and bolt hole pattern.

Can I use Brand X oil in my fan drive?

Answer: In general, lubricants that meet AGMA #5 are recommended for use in our cooling tower fan drives. In addition, lubricants must be compatible with nitrile and viton seals, Amarillo’s lacquer-based gear case sealer, and sprag-type backstops. Extreme pressure lubricants are not recommended. Assuming a product meets these requirements, it may be used in our cooling tower gear drives.

During cold weather operation, when are heaters and/or synthetic oil recommended?

Answer: Oil heaters with thermostats are recommended whenever the fan drive will be started with an ambient temperature around the gear drive of 20°F and below. If hot water flowing through the tower maintains the ambient temperature above this limit for a period of time prior to start-up, then heaters are not required.

It is important that the oil is above its pour point temperature prior to start-up. Starting the fan drive when the oil temperature is below the pour point will result in no oil flow to the upper bearings and possible damage to internal components. Very viscous oil can cause oil slinger screws to shear and can overload the shaft on optional positive displacement oil pumps.

Synthetic oil has a much lower pour point than mineral oil. The synthetic oils listed in our O&M Manual may be used in our fan drives, without a heater, when the gear drive ambient temperature is -20°F and above. However, keep in mind that synthetic oil is expensive. Additional advantages are listed in our O&M Manual.

Below -20°F, synthetic oil and heaters are required.

Ambient Air Temperature Recommendation
Greater Than 20°F mineral or synthetic oil
20°F to -20°F mineral oil with a heater / thermostat, or synthetic oil
Less than -20°F synthetic oil with a heater / thermostat

What modifications does Amarillo Gear Company recommend based on ambient temperatures around our cooling tower gear drives?

Answer:

Ambient Air Temperature Modification Required
Less Than 120°F None
120°F to 150°F Synthetic Oil or Viton Seals
Greater than 150°F Synthetic Oil, Viton Seals, External Cooling

What are the pros and cons of adding an oil filter to a gear drive?

Answer: The main benefit of an oil filter is that it removes most of the particles that cause abrasive wear on the gears and bearings. This will extend the service life of the gear drive if oil is changed at recommended intervals. It is important to understand that an oil filter does not prevent oil contamination from water or oxidation. The main causes of premature failure in cooling tower fan drives is low oil level or poor oil quality, not abrasive wear. Oil filter elements require replacement, so maintenance costs are higher when using an oil filter, and the external plumbing increases the potential of an oil leak.

Describe how the oil filter system works on a double reduction fan drive?

Answer: The filtering system used on a double reduction fan drive utilizes a positive displacement pump that is driven by the intermediate shaft. The pump forces oil through the filter mounted on the outside of the gear case. The filter contains a 75 micron, acrylic fiber element that has low pressure drop. The filter housing has a built-in bypass valve to ensure oil flow with a clogged filter. After filtering, the oil is routed inside the gear case where it is distributed to the bearings and gears using a manifold system.

Why doesn’t Amarillo Gear recommend EP oils?

Answer: A customer may elect to use an Extreme Pressure (EP) lubricant; however, Amarillo Gear Drives do not need the EP additives to operate properly. In fact, EP additives will prevent our sprag non-reverse devices from properly functioning.

In the past, data from bearing manufacturers had suggested that EP lubricants might extend bearing life. At that time, we recommended EP lubricants in gear drives without a sprag type backstop. However, current research indicates that some EP additives may reduce bearing life. Because Amarillo Gear has a long history of gear drives in service using non-EP oils, we conservatively decided to take EP oils out of our O&M Manual.

Does my fan drive need a mechanical oil pump?

Answer: Often, mechanical oil pumps are specified because many of our competitor’s gear drives require the oil pump for lubrication. This is because they sell multipurpose, “industrial”, gears that are adapted for use in cooling towers. Amarillo Gear Drives are designed specifically for cooling towers and use an oil slinger system that operates in either direction. A mechanical oil pump on our fan drives is an extra cost option, but is not required. The oil slinger is installed and functional, even when the oil pump is added.

Our oil pump is truly bi-directional. It will pump in either direction while using the same suction and discharge ports. Many years ago, we worked with Viking Pump to design and manufacture this bi-directional oil pump. The reason other gear drive suppliers warn against running in the reverse direction is that they use a standard unidirectional oil pump and they do not have the oil slinger as a redundant system.

What is the minimum oil level below the normal oil level for fan drives without oil pumps?

Answer: The minimum oil level below the center of the sight glass is shown for each model below. These should be considered absolute minimums (3/4” of oil on slinger); oil levels below those shown may result in loss of lubrication and gear failure.

Model Min Oil Level Below Normal
6 .75
85 .75
110 1.50
135 1.75
155 1.25
175 1.75
1008 .75
1110 1.19
1311 1.31
1712 1.69
1713 1.69
1814 1.69

Will “wind milling” damage my cooling tower fan drive?

Answer: During short periods of several hours, wind milling of the fan poses no problem for the gear drive. During wind milling, the speeds are low and the load on the bearings is light so the existing lube film is adequate. If the fan windmills for extended periods of time, it is possible that the bearings could lose their lube film causing damage. In these situations, our optional mechanical oil pump is recommended on double reduction fan drives, and the optional electric oil pump is recommended on single reduction fan drives. Both options will supply fresh oil to the bearings regardless of the wind milling speed, direction, or duration.

Does my gearbox need to be aligned? If so, what are the tolerances?

Answer: Gearbox alignment is critical for a smooth and quiet running gearbox with a long trouble free service life. If the gearbox is grossly misaligned, the driver (motor or engine) cannot transmit uniform rotation to the gearbox. Consequently, the following problems may occur:

  • Vibration
  • Noisy running
  • Reduced bearing life
  • Premature gear tooth failure

Basically, the input shaft of the gearbox and the output shaft of the driver should be parallel and the centerlines of both shafts should be in a common vertical plane.

Many different types and makes of drive shafts are being used. The tolerances for the shaft angular misalignment vary. Typically, a gearbox can tolerate larger misalignment than can a drive shaft. Consequently, Amarillo Gear does not set the tolerances for shaft alignment. Rather, the tolerances should be obtained from the drive shaft suppliers.

What is a bearing’s “L10a” rated life?

Answer: L10a rating life is the life that 90% of a group of identical bearings will exceed before a fatigue spall develops, with adjustments for material, reliability, and operating conditions.

Where should I put a vibration sensor on the gearbox?

Answer: It is recommended that vibration transducers be placed at the locations shown on Form 612 (fan drives). If specified at the time of order, we will drill / tap / spot-face vibration transducer locations on the gear drive. In the field, however, to avoid the possibility of drilling through the gear case and creating a possible oil leak, it is recommended to attach sensors using epoxy mounted thread blocks in the specified locations.

What hardware and torque is used to install my fan drive in the tower?

Answer: Hardware and torque is specified in Amarillo Gear Engineering Form 551.

What is the Warranty policy for new vs renewed gearboxes?

Answer: Both a new and renewed AGC gearbox have a warranty of 12 months from install date or 18 months from shipment date. Marley warranties can be extended to up to 24 months.