Blowers and Cars per Hour (CPH) - Professional Carwashing & Detailing
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Blowers and Cars per Hour (CPH)

When out in the field, I often hear the question “Why are the cars still wet?”


When out in the field, I often hear the question “Why are the cars still wet?” Well, that is a good question and one that needs to be looked at from many different angles.

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There are some things that are a must in order to get a clean, dry and shiny car:

  1. Temperature – the ambient air and surface temperatures of the vehicles. The colder the temperature the harder it will be to dry the car. In winter months you may want to use a little bit of heated water in the drying process.
  2. Mechanical action – the number of pieces of equipment that touch the vehicles. If the surface is not clean it will inhibit the drying process. Look for any piece of equipment that is out of adjustment that may be contributing to this problem.
  3. Chemical concentration – the strength at which the chemicals are applied to the vehicles. With all chemicals especially your drying agent, more is not always better. If you use to much it will not allow the cars to dry. You need to find the middle ground.
  4. Time – the amount of time the chemicals have to work. This is something that needs to be looked at when it comes to drip space. You need to have a good amount of drip space or none. The old way is having a large amount of drip space, today most new car wash locations use a flash or continues dry process.
  5. Water quality – the hardness and pH levels can have an effect on the finished product as well. If the surface of the vehicle is not low pH around 6.5 or less the car will still be wet. You need to check the pH of your water and chemical makeup to insure this is not a problem.
  6. Position- Blower position angle and nozzle type can also have an effect on the way the cars are coming out. Look to use round nozzles for the top blower nozzles and curved nozzles for all side surfaces. The angle adjustment is something that will need to be fine-tuned over time.

The number one cause for wet cars is chain speed or CPH in relation to blower horsepower or time.


So what should the CPH be? If all of the above are in line, then you would use the one-to-one rule to determine the correct CPH. That is, for every car per hour the conveyor is run, there should be one horsepower of blower. Let’s say the chain speed is set at 120 CPH, then a 120 horsepower blower system should be in place.

The thing about rules is that they are meant to be bent or even broken. If you have the right chemical and equipment set up, the CPH rule can be exceeded by 15 to 20%. If everything was set up right in the wash, the same 120 horsepower system could be used at 138 to 144 CPH and still deliver dry cars.


Robert Andre is the President of CarWash College™. Robert can be reached at [email protected]. For more information about CarWash College™ certification programs, visit CarWash College or call the registrar’s office at 1-866-492-7422.

This content is sponsored by CarWash College. Sponsored content is authorized by the client and does not necessarily reflect the views of the Professional Carwashing & Detailing editorial team. 

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