Crossdraft booths all suffer from a physics problem. As a general rule, the exhaust fan in an automotive spraybooth moves about 10,000 cubic feet of air per minute (cfm). By design, the air enters at one end of a crossdraft booth, is dragged along the length of the vehicle and then exits at the other end.
The physics issue is the space between the top of the vehicle and the ceiling of the booth, the narrowest part of the air’s travel path. Because the fan is constantly pulling 10,000 cfm, the air must speed up to fit through the narrow space above the vehicle. Once the air gets to the front edge of the roof that meets the windshield, more space is available and the air slows down. When the air slows, it drops some of the dirt it was carrying along.
If you’ve headed the car into the booth, the dirt will drop on the hood. The old axiom is that two parts of the car must be flawless – the driver’s door and the hood – because the owner sees both every time he drives the car. Since you can’t change the way a crossdraft booth works, change the way you place the car in the booth. Back the car into a regular crossdraft so the dirt will fall out of the slowing air onto the deck lid instead.
Writer Mark Clark, owner of Professional PBE Systems in Waterloo, Iowa, is a well-known industry speaker and consultant. He’s been a contributing editor to BodyShop Business since 1988.
