Sealing the Gasket on a Spray Gun Cup

[Julie Moriarty]

I have a Fuji XPC spray gun. I've read they are notorious for leaking at the cap. Mine has lived up to that reputation. When I'm spraying WB finishes, I wet the gasket with water and that does the trick.

I've been spraying lacquer lately and I've just been trying to tighten the cap best I can. Sometimes it works, sometimes it doesn't. It leaked badly today and I started wondering if I could use spray gun oil on the gasket? If not, does anyone have any idea what I could use to create a better seal?

[Jamie Buxton]

I have the same gun and the same problem. I've never heard of your water fix before, and will try it the next time I have the gun out.
My current fix is the get-a-bigger-hammer approach. I put on a pair of those high friction gloves, grip the can and the cap, and twist as hard as I can. It works for waterbornes, which is nearly all I shoot. It might work for lacquer. I'm leery of putting oil near a spray gun for fear of fisheyes.

[Harry Hagan]

What’s the problem? Is it a poorly designed gasket that leaks when it’s still in good condition—or is it simply worn out and needs to be replaced? If it’s the former I’d be contacting Fuji.

[Julie Moriarty]

To cure the problem last time, I replaced the gasket. It was only a month old and had only been used to spray one quart of lacquer. Based on everything I've read, I'd say the problem is the gun. Maybe if they had allowed for the ability to screw the cap on tighter, or designed in a better gasket, this wouldn't be a problem. But it seems if the gasket is dry, the cup leaks, unless the gasket is new, as in never been used. If any finish gets on the gasket, which happens no matter what you do, then it leaks the next time you use it.

[Peter Rust]

I had the same problem with my Fuji gun and they sent me a replacement top with more scallops on the outside of the lid that let you tighten it more easily. This replacement top worked for a few weeks and then leaded as well. I found that the leaking was due to finish drying on the gasket or under the gasket in the channel that the gasket fits into. I solved the problem on my gun by removing the gasket each time I spray, cleaning the channel in the top and cleaning the gasket. I also took the replacement lid that Fuji sent me that was leaking, removed the gasket and found dried paint underneath. I took small screw drivers and thoroughly cleaned the channel, replaced the gasket and that top now works without leaking.

Hope this helps.

Peter

[jesse ross]

I also had the same gun and the same problem. Fuji is an excellent company but they freely admit the rubber used for the gasket isn't perfect, especially with solvents.

Luckily there is a solution. Buy the pps cup system (I believe devilbliss also makes one.) The PPS is a plastic cup and lid with replaceable liners. You buy a set of liners & lids, as well as a small stainless steel connector that stays on your gun. The beauty of this system is your finish never touches the cup. You drop the liner into the cup, fill it, screw the plastic top on & connect the gun to the cap (an easy click and turn.) I have the gravity model, so the gun connects upside down. The cup system also comes with a long tube that replaces the original fuji airtube that diverts a portion of the airflow to pressurize the cup. Once attached, you simply turn on the turbine and hold the trigger down, and the inner bag of finish compresses until all the air is gone and pure finish comes out. Until that point however, you keep the cup oriented so the cap side is up. With a syphon cup, the gun is in a normal orientation, with a gravity system, the gun is held upside down. Once the bag of finish is crinkled into a an airless clump there is pure delivery of material to the wood and the gun can be held in any orientation. No dripping, no uneven spraying, and if you take a break you can leave the cup in any position. When you're done you remove the airhose from the cup, hold the trigger down again, and wait till in fills with air and returns to the original shape. Gun easily disengages from the cup, and the only cleanup necessary is easily accomplished with a small squirt bottle of the appropriate solvent right into the connecting valve where the cup connected to the gun. After a few uses you'll confidently chuck that crusty old metal cup and lid into the trash. This will improve your spraying immeasurably.

I bought mine from roger phelps who is a supremely straight shooter, but I have no affiliation with him or pps whatsoever.