Correcting Leaks and other Material-Related Problems

The other “family” of problems with a spray gun involves the materials being sprayed – primer, paint, clear coat, and so on – rather than the air supply itself. There are more of these problems than air system faults that a painter may need to contend with, and solving them is generally more complex because of the multiple possible causes for each specific difficulty.

The most obvious material problem is if paint or primer leaks out around the nozzle area, and this can be quite harmful because of the possibility of blocking the orifices in the air cap or the wing ports, possibly irrevocably if they are not cleaned in time. One of the most common causes is that paint needle valve is sticking open slightly, allowing some paint to dribble out when it should not.

The needle passes through an area of packing, which may become compacted and grip the needle too hard. Remove the needle valve by screwing the material control knob looser until it comes free, and then clean the needle, lubricate it with purpose-made spray gun lubricant, and loosen the packing slightly.

A compression spring is also built into the paint needle valve, allowing it to spring back into place when the trigger is released. If this has become flabby and worn out over time, it may no longer push the tip of the needle fully into the nozzle tip, allowing paint to escape around the needle. The spring needs to be replaced in this case, and the needle tip and nozzle should also be checked for damage that causes them to fit together improperly. Replacement is the only answer in either case.

If the material leaks out around the packing – which is roughly halfway between the trigger and the nozzle, on the underside of the gun – then the packing nut, or gland nut as it is sometimes called, needs to be tightened to hold the packing in place more firmly. If this does not work to stop the leak, then the packing nut should be removed and the packing itself replaced. The packing is needed to keep the paint from flowing back along the paint needle valve’s channel and dripping out near the trigger.