Spray Equipment Setup, Operation, and Troubleshooting
What the exam tests
This domain focuses on spray equipment setup, operation, and troubleshooting: gun types, fluid tips and air caps, pressure settings, pattern testing, cleaning, and common faults such as spitting, fluttering, uneven fan, and fluid leaks.
Core rules
- Identify the gun type and feed system. Gravity, suction, and pressure-feed guns set up differently; use the manufacturer's settings for the material.
- Match fluid tip, needle, and air cap as a set. A mismatched set changes fluid flow and atomization even if the gun looks assembled correctly.
- Set inlet pressure with the gun triggered and fluid flowing. Static pressure readings mislead because the regulator may not flow enough air.
- Test the pattern on paper: the fan should be even, with no heavy center, split, or tails. Adjust air and fluid separately, then recheck.
- Keep the vent in the cup or pressure pot clear. A clogged vent causes spitting, starvation, or a collapsing fluid supply.
- Clean the air cap, fluid tip, and needle with a soft tool and correct solvent. Do not probe orifices with wire; it changes the spray pattern.
- Replace worn packings and seals. A fluid leak at the packing nut or a fluttering needle indicates wear or incorrect adjustment.
Worked example
A gravity gun spits a drop of paint at the start of each pass. The technician checks the cup vent, finds it clogged with dried material, clears it, and the spitting stops. The reasoning: a blocked vent prevents air from replacing the fluid leaving the cup, so flow becomes uneven. If the vent were clear, the next checks would be the fluid tip, needle, and packing.
Traps that cost marks
- Soaking the entire gun in solvent and damaging seals.
- Using a wire or drill bit to clean the air cap.
- Adjusting fluid flow to fix a pattern caused by air pressure.
- Ignoring a worn tip and increasing pressure to compensate.