It will happen from time to time. You load up your spray gun to coat a part and you notice your spray gun leaking. A spray gun can leak for a number of reasons but all are fairly easy to diagnose and fix. 90% of the time a material leak will come from the nozzle area where the needle comes into contact with the nozzle. Below are a few reasons why this could be happening as well as quick ways to rectify it.
1. There could be some buildup or even a small foreign particle in the nozzle itself that could cause your spray gun leaking. A quick way to check this is to load up your spray gun with cleaner or water, turn up your material pressure a bit, and quickly trigger on and off your spray gun several times. This should cause enough pressure and movement to break loose whatever is in the nozzle and expel it outward with the spray of the gun. If this does not work you may have to remove the nozzle itself and clean it out manually with solvent and a brush/pick. *Always remember to loosen the needle spring to take pressure off the needle before removing the nozzle; not doing so can cause damage to both*
2. There could be some buildup on the needle. In this case you would have to remove the needle and manually clean it with solvent to ensure the entire surface is smooth and clear of any foreign objects or obstructions.
3. Your needle adjustment screw could be turned back too far (for information on what a needle adjustment screw is see the article here). This means that the needle is set so far back that it is allowing small amounts material to flow around the tip of it and out of the nozzle. An easy way to check this is to look at the front of the spray gun and see how the needle is coming into contact with the nozzle at the tip. They should be flush and there should be no gaps. If there are, try tightening down the needle adjustment screw and this should push the needle forward so that it is flush against the nozzle in order to provide an adequate seal when closed.
4. Your needle spring could be worn and need replacing. There is a spring behind the needle that pushes it forward so it seats against the nozzle when the gun is not being triggered. When this spring wears it will not have the strength to fully push the needle forward anymore and thus there will be a gap allowing small amounts of material to pass through the nozzle when the gun is not being triggered. You would need to replace the needle spring. Refer to your manual for the part number and call your spray gun supplier to order the necessary part.
5. The needle/nozzle itself could be worn or damaged. The needle and nozzle are both wear parts on any spray gun and over time that will wear to the point of failure. If you have tried all of the above steps and you are still getting a leak, then this is most likely your issue. Refer to your manual for the part number and call your spray gun supplier to order the necessary part.
Jorge Flores, Marketing Coordinator
Coating Equipment Technology, Inc