How to treat Gearbox to make cooling tower run efficiently

Last updated: 31 May 2024

     It is very important to maintain the full efficiency of Cooling Tower across several industries. One of the major and important components in the operation of Cooling Tower is Rotating Part equipment which have the function to cool down and maintain the stability in the system. If someone still in doubt about the component in cooling tower please refer the article that we ever post before about component of cooling tower including Rotating Part and Static Part.

     In this article we will mainly focus on the Rotating Part of Cooling tower about each part function, how to maintain it, and the method to inspect it correctly to ensure that your cooling tower is operating at the full efficiency all the time. One of the important equipment in Rotating part that plays an important role in the operation of cooling tower is Gear Box, which we will explain in detail in this article.


Gear Box or Gear Reducer

     Gear Box or Gear Reducer play a role to reduce the speed of motor in order to drive the fan in the system. Normally cooling tower used 4-pole motor* to drive the fan blade, which a standard speed of the 4 poles motor at approximately 1,500 rpm.  We cannot drive the fan blade straight away because this will cause the tip speed of the Blade (Tip Speed) to be too high. According to the standard of Tip Speed it must not exceed 61 meters per second, in case the Tip Speed higher than this figure, there is a high chance of vibration occur which will cause damage later.

* Poles is the number of magnetic poles that create a magnetic field inside the motor. The more poles there are, the rotational speed of the motor will be lower.

In order to calculate the tip speed of the propeller, the equation will be used as below :


For example, to calculate the propeller tip speed : If the propeller has a diameter of 7.32 meters and rotates with a speed of 150 RPM

Tip Speed = 73.2 * 3.14159 * 150
Tip speed = 57.49 m/s


If the calculation of Tip Speed is found out to be more than 61 m/s as specified by the standard, there are 2 options to adjust :


Method 1: Use Gear Box or Gear Reducer to reduce the speed. 

There are 3 main types of Gear Reducer :

     1. Helical Gear Drive

  • It is gear that is designed to attach to the factory gear by gear shaft and motor shaft will turn in the same direction.
  • Commonly used in small Cooling Towers.
  • A common problem for this type of gear is that the Motor and Gear Reducer are always in a humid state.
  • Therefore, you need to maintain the Gear frequently and it is easily damaged or has a shorter lifetime than normal standard.

Picture 1 : Helical Gear Drive

     2. Belt Drive

  • It reduces the speed of GearBox by using the belt.
  • Generally, used in small cooling tower
  • Frequent maintenance is required due to the belt tension which must be maintained throughout the time.
  • The drawback is that the belts often break due to high humidity and loss of energy due to belt failure, which causes power transmission not fully operate and part of the energy lost due to the heat or friction.

Picture 2 : Belt Drive

     3.Right Angle Gear Design

  • This type of Gear Box has the input and output gear shafts 90 degrees perpendicular to each other, so when choose this type of Gear there must be drive shaft connecting the gear and motor to transmit the power from the motor to the speed reduction gear (Gear Reducer) and Fan Blades.
  • This type of gear is designed to have more durability than the first two types of gear because the motor is installed outside the Cooling Towers upper structure (Stack) to prevent it from directly exposed to moisture and the Gear Reducer inside the cooling tower will be exposed to direct humidity. However, it will not affect the operation because it is specially designed to tolerate high humidity conditions which result in longer lifetime.
  • According to CTI (Cooling Tower Institute) ESG111 standard defines that the design of Gear Reducer for Cooling Tower must be able to work in conditions that can be encountered with the humidity and full efficiency in operation. Therefore, ordinary Gear is not suitable for using in cooling tower that have high humidity.
  • Commonly used in large Cooling Towers.
  • Alignment for this type is more difficult than the first two types due to the size of the Drive Shaft being longer. Therefore, it requires expertise with an experienced technician to install


Picture 3 : Right Angle Gear Reducer


Method 2 : Changing the number of Pole Motors

The speed of each pole motor using are as below :

  • 2 Poles Motor: Approximately 3,000 rpm.
  • 4 Poles Motor: Approximately 1,500 rpm.
  • 6 Poles Motor: Approximately 1,000 rpm.
  • 8 Poles Moter: Approximately 750 rpm.

The speed of the motor can be calculated from the below equation

     If you want the speed of the motor to be increased or decreased, you can choose the number of motors. We can used various type of poles according to the usage and design of the system that needs to be used and can accurately calculate the motor speed from the above equation. Therefore, this way will help you to select the motor appropriate to the operation.

     Therefore, most of the time, Cooling Towers must have Gear Reducer to reduce the motor speed appropriately. It is very important to choose the right motor and gear box together with maintaining it efficiently to ensure the safety of cooling tower system.


How to repair and maintenance a GearBox or Gear Reducer 

     It is very essential for repairing and maintenance a Gearbox or Gear Reducer need to use the well experienced expertise. The operation consists of the following important steps

  • Changing the Oil Engine : Gear reducers usually need to change the oil engine on a timely basis, the standard is the same as changing the oil engine in the car in order to ensure that the lubrication system works efficiently.
  • Inspection and replacement of Bearings (Bearing) : Normally, bearings must be specially designed to receive the load and the thermal rating (cooling) must be designed to be sufficient enough to use properly. The lifetime of Bearing in the cooling tower must not be less than 100,000 hours. If we find that the Bearings close to expiration it should be overhauled to replace the bearings, oil seals, O-rings and shims, etc and including the inspection of internal gear condition. 


The problem in Overhaul Gearbox which we always found is that selection an inexperienced Mechanic who have not enough skill up to the standard will lead to :


  • Failure to properly set Backlash and Bearing End Play: this will result in shortened lifetime of Gear Reducer or damaged prematurely and Using the wrong Shim Material: Some materials can shrink when exposed to high temperatures, this causing the set value becoming inaccurate and damaged.

 Article about a case study of overhaul gearbox >>> Is it true that it won't matter much who fixes the gearbox?


     The decision to choosing the Mechanic with inexperience or choosing just because of the price factor will lead to saving money in short term in most cases. It looks like maintenance of the car in the Garage is not up to the standard instead of being taken into the Certified Service Center which have an expert technician to maintain the car. 

     It is definitely worthwhile in the long run if we invest to choose the technicians who have experience and knowledge for overhaul and maintenance because it helps to ensure that the various components in cooling tower get proper care to reduce the risk of damage or shorter lifetime than it is supposed to be.

     Additionally, after Overhaul Gear is completed, it is essential to choose the Service Center that has a Running Test Gear Machine to ensure that the system of sound, temperature and vibration does work well and up to the standard before being brought back to the actual installation and use it. This will help to detect the potential problem in advance, reducing losses, time and expenses from subsequent unnecessary repairs.

     Ultimately, choosing the Service Center that has thoroughly tested your device is the best way to prevent it from the problem that may occur and reduce the risk along with the inessential cost for long run.

     Last but not least, we do hope that this article will be useful to readers. If you have any questions or query about cooling towers, or have any idea for our next article please contact us or make suggestions through our email We are ready to give advice and answer your questions for free from our experienced and well-trained expertise. 

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