12-10-2009, 05:16 AM
doctorwayne Wrote:Why not mount it on the top? I have mine mounted at the top rear of the booth, gaining access to outdoors with only one 90 degree bend. Mounting it on the top will also shorten the run.
I've been looking at building my own spray booth and came across this thread. Here's a little intel from the world of spray booths:
As for venting to the top of the booth (updraft booth), in the real world it's just not done that way. This can have adverse affects on both booth performance and finish quality.
It's important to understand what happens when you vent to the top of the booth. First, you're working against gravity; that means you'll need higher airflow rates for proper ventilation. Secondly, the updraft pulls the atomized paint away from the part, requiring higher spraying pressures to compensate. The resulting finish problems created by high airflow rates and high spraying pressures are further compounded by the limited adjustments on airbrushes (versus conventional spray guns), and limited thinners and reducers available for hobby paints. Although automotive thinners and reducers have been used in hobby applications, their corrective properties may not be sufficient to overcome a poorly designed spray booth. Finally, when venting to the top of the booth, there is a good chance that overspray particles in the filter will fall down into the paint. It's not a good idea to hang dirt above the part you're painting.
Cross-draft (fan @ the back) or down-draft (fan @ the bottom) are the way to go.
Also, I've found that for the size of the booths we are building, we need 300-350 CFM blowers for proper air movement. There's a fancy math formula used to figure out your CFM requirements, and it also depends on your ductwork and other factors.
Tony