The basic spray booth may be no more than a steel box capable of removing spray mist with simple filter extraction, which may prove quite adequate for some shops to comply with current legislation.

There are 4 criteria which the booth must meet:

1) That it provides a safe environment in which to spray.

2) That it is capable of producing clean jobs.

3) That it is capable of achieving fast enough through put from baking/curing cycle.

4) That vehicles can enter and exit the booth quickly and easily without hold-ups.

Apart from the safety aspect, the booth must be capable of producing clean jobs. That means that as large an area as possible of the roof must contain filter material, that it must be well seated into the retaining frame and that it must be changed regularly.

The filter material is coated with a sticky resin, so as dirt particles become trapped within the filter medium, they will restrict the air flow, therefore the booth must be balanced (air in and air out) regularly.

During the spray cycle all the air pumped into the booth through the filter is exhausted and should be maintained at a temperature of l8-23'C for optimum application conditions.

When on bake cycle, the air is circulated through the heating plant and around the booth with a 10% bleed-off to prevent explosive mixtures of vapours to build up. The booth should be capable of reaching 80°C air temperature within 10 minutes of bake cycle and needs a burner of 500,000 B.T.U., 150 kilowatts or more to achieve this.

Booths without insulation, (single skins), will lose more heat into the workshop on a cold day and required temperatures may never be reached.

Booth manufacturers make a feature of the number of air changes per minute a booth has. If a booth is 7m long, 4m wide and 2.8m high, its volume would be 78.4 cubic meters, and if the air changes were rated at 4.5 times a minute, the booth would require 350 cubic meters of air every minute.

Now, if we put a transit van into that same booth and the measurement of that van was 2m high, 2m wide and “m long, the van would fill 16 cubic meters of air, which would not be moving, so the booth volume is reduced to 62.4 cubic meters. The fans would still move 350 cubic meters and the booth is up to 5.6 air changes per min.

A more important measurement is that of air speed. If all the air in the booth is moving at a constant rate down with the booth of 50-120 linear feet (l6~40 meters) per minute, an even spraying environment is produced, but often booths have areas of faster air movement which can lead to turbulence, slow air movement or dead spots with no air movement.