CALCULATING AIR FLOW IN SPRAY BOOTHS

Q:  What is the recommended booth pressure during spray & bake mode? Why?

A:  If you have an air make up system (push air into the booth and pull air out of the booth) then the pressure differential between the inside and outside of the booth should be 0.03-0.07 inches water column (W.C.), [0.08 - 0.17 mm W.C.] either positive or negative. The advantage of having a slight negative pressure is that you keep the vapors out of the factory working area. On the other hand, when you operate under negative pressure you have the potential to draw dust into the booth.

Q:  What is the total air requirement per hour during spray & bake mode? Why? We have a booth of size of 7.5m (length) x 3.90m (width) x 2.65m (height).

A:  Until recently, in the US the air velocity was recommended at 100 ft/min (30.48m/min) (minimum). This was to ensure that the painters were properly protected from inhaling the vapors and paint particulates. Also, at this velocity one is reasonably sure that the LFL is low enough to prevent a fire or explosion of the vapors. Currently the guidelines for air flow are based on the LFL and not on velocity. However, I believe that most people still go by the 100 fpm minimum, (although I cannot confirm this.)

To calculate the air flow in cfm (cubic ft per minute) you multiply the velocity x facial surface area of the spray booth filters. I assume that in your case the booth will be cross draft, and the surface area through which the air passes is 3.90m x 2.65m. Therefore the volumetric flow rate is 315 m3/min. You do not need to incorporate the length of the booth, unless it is a down draft spray booth.

Q:  What is the recommended air velocity during spray mode? Why?

A:  Already answered.

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