Most spray gun complaints are not broken guns. They are a plugged horn hole, a dry packing or an air/fluid balance that is off. Binks' troubleshooting guide (SB-2-001) and pattern chart (03-528-01) boil it down to a method: spray a test pattern, read the shape, then fix the one thing that shape points to. This article applies to any conventional or HVLP air spray gun, including the Binks 2100, JGA, MBC and Trophy.
1. The static pattern test
- Confirm the air cap, fluid tip and needle match the material.
- Tape a 20 in. square of brown paper to the booth wall at shoulder height.
- Set the recommended inlet pressure, hold the gun at the normal distance (6–8 in. HVLP, 8–10 in. conventional) and hold the trigger without moving until the paint starts to sag.
- A good pattern is symmetrical and evenly wet from top to bottom. Anything else is one of the faults below.
2. Pattern faults
Binks Data — Spray Gun Troubleshooting Guide SB-2-001| Condition | Cause | Correction |
|---|---|---|
| Heavy top or bottom | Horn holes plugged, or dirt on top/bottom of fluid tip | Clean; ream with a non-metallic point |
| Heavy right or left | Horn holes on that side plugged, or dirt on the tip | Clean cap and tip |
| Heavy center | Fluid pressure too high for the air, material too thick, or atomizing air too low | Reduce fluid flow, open the spreader valve, thin, or raise air |
| Split pattern (heavy ends) | Air pressure too high, fluid too low, or fluid knob turned in too far | Reduce air, raise fluid pressure, back the fluid knob out |
| Starved pattern | Not enough material, or low atomizing air on siphon/gravity guns | Back fluid screw out to first thread or raise tank pressure; clear cup vent |
| Cannot get a round spray | Fan adjustment screw not seating, or retaining ring loose | Clean or replace; tighten ring |
| Will not spray | No air, wrong cap/tip for feed type, fluid too heavy, fluid screw closed | Check air; fit suction cap and tip; thin or go pressure feed; open screw |
Table 1 — Pattern faults and the single correction for each.
3. Leaks, spitting and flutter
| Condition | Cause | Correction |
|---|---|---|
| Jerky or fluttering spray | Loose or damaged fluid tip or seat (the most common cause); low material; cup tipped; dry packing; loose fluid tube | Tighten or replace tip; refill; lubricate or tighten packing nut |
| Fluid leaks from packing nut | Nut loose, packing worn or dry | Tighten without binding the needle; lubricate or replace packing |
| Fluid drips from front of gun | Packing nut too tight, dry packing, worn tip or needle, dirt in tip, broken needle spring | Loosen slightly; lubricate; replace tip and needle as a matched set |
| Spitting | Air entering the fluid passage through a dry packing, dirt between fluid nozzle and seat, loose swivel nut | Two drops of oil on the packing; clean nozzle seat and tighten; tighten swivel |
| Air leaks through gun at rest | Air valve not seating, or valve stem packing worn | Clean and inspect valve and body; replace stem packings |
Table 2 — Leak and flutter faults. On MBC guns a needle that binds can also mean a misaligned spray head: tap around the head with a wooden mallet and retighten the lock bolt.
4. Finish defects
- Runs and sags: too much flow, material too thin, or gun tilted. Reduce fluid pressure or tip size, hold the gun at right angles.
- Dry, sandy finish: gun too far away, air too high, or wrong thinner. Check distance and drop the air.
- Orange peel: gun too close, tip too large, air too low, or a dirty surface. Check distance, raise air or drop fluid pressure.
- Excessive overspray or fog: air too high, gun too far, too much fast thinner, or arcing the stroke. Reduce pressure and move at a steady pace parallel to the work.
5. The lubrication points
Daily, and after every trip through a gun washer, put spray gun lube on the fluid needle packing, the air valve packing, the trigger bearing screw and the adjusting-screw threads. Lightly coat the needle spring with petroleum jelly and clean and lube the air cap and baffle threads. Never soak the whole gun in solvent, and never use silicone lubricants. When the packing nut bottoms out, the packing is done: replace it rather than tightening further.