Compressors and Spray Booth Operations
Compressors and Spray Booth Operations
This domain tests compressed-air supply, air quality and the safe operation of a spray booth. Questions often involve compressor sizing, water/oil contamination and booth airflow.
Compressor and air line
- A reciprocating compressor is common in small shops; a screw compressor suits continuous demand.
- CFM or FAD is the delivered free air at a stated pressure. Add the demand of all tools running together and allow a margin.
- A receiver smooths demand; a regulator sets line pressure; filters and a coalescing unit remove oil and water.
- A refrigerant or desiccant dryer lowers dew point. Water in the line causes fish eyes, blushing and poor adhesion.
- Drain receiver and filter traps regularly.
Booth operation
- A downdraught booth pulls air from the ceiling through filters and exhausts at floor level.
- Intake and exhaust filters must be clean and correctly fitted; a loaded filter reduces airflow and causes overspray and solvent build-up.
- The booth should be kept at slight negative pressure relative to the workshop so fumes do not escape.
- Use explosion-proof electrical equipment and bond/earth the workpiece and gun.
- Check airflow and filter condition before each shift.
Worked example
A spray gun needs 8 CFM at 90 psi. The compressor delivers 6 CFM FAD at 90 psi. The combination is inadequate because the gun will starve, pressure will drop and atomisation will fail. The correct action is a larger compressor or a lower-demand gun, not simply raising the regulator set point.
Traps
- Ignoring water in the line and blaming the paint for fish eyes.
- Using a compressor with a low duty cycle for continuous spraying.
- Blocking booth filters to save money, then getting solvent odour and overspray.
- Failing to earth the workpiece in an electrostatic or solvent environment.