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Ask the Expert Question-and-Answer Archive

by Ron Joseph

September, 2006

Spray Booth Operates at High Positive Pressure

Q: Hi there, I work at a Automotive Panel & Spray shop in Wellington New Zealand, and we are having some trouble with our booth and would really appreciate some advise from you, the problem is booth pressure, at the moment the doors on either side of the booth pop open constantly and over spray is forced out through every door seal and gap, the booth used to work very well, but slowly over time the doors are getting harder to shut, which I think maybe the exhaust ducting might be partially blocked by paint spray, we recently cleaned about 1 cm of built up off the exhaust blades and removed 12 cm from the exhaust ducting walls, there is still an area in the exhaust ducting where we haven't yet cleaned because of accessibility to that area, so this maybe the problem.

It seems that the exhaust fan is not removing the air fast enough or that the inlet fan is forcing in too much air to the booth, we have increased the pitch on the exhaust fan fins but with no success.

Any advise will be greatly appreciated as this problem is effecting the running of the business.

A:  You are absolutely correct. You are choking off the exhaust air by allowing the overspray to build up in the exhaust duct.  Moreover, this can be a major fire hazard and unless you remove all the overspray from the duct and the fan blades you can anticipate having a booth fire at some time in the future.   But the real problem is that you are using filters that do not capture the overspray.  You should be able to operate a spray booth for years without building up overspray in the exhaust duct. I'm sure you have excellent filter suppliers in New Zealand and certainly in Australia, but please visit the sites of some American filter companies to see what types of filters are available.  For starters I suggest that you visit, and When you review these sites look for two-stage filters, since these are the ones I suggest that you use. The companies often refer to them as Aerospace NESHAP compliant filters, but that terminology simply means that they comply with an American regulation for aircraft painting operations. Despite the reference to aerospace, you can and should also consider their use in your booth. The filters will be more expensive than the ones you currently use, but the cost is worth paying, especially if you can avoid having to scrape overspray off the ducts and if you can prevent a spray booth fire that can burn down your entire shop.

Best wishes,

Ron Joseph

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