Atro roofing gun leaking air out the top vent continually how do i know which o ring to replace to stop the leak

you may have to rebuild it again. inspect nail gun piston cylinder to ensure that it is not worn or scratched. Is the gun lubed before each use and periodically under heavy use?. Water from compressed air will damage gun.Use quality parts use buna n o rings not buna o rings
good luck

https://www.ereplacementparts.com/repair-center/article/7451/How_to_Install_an_Overhaul_Kit_in_a_Porter_Cable_Nail_Gun.html

I had the exact same problem after doing a complete rebuild. If you are using the Stanley bostitch rebuild kit, check to see if you accidently swapped o-rings 6 and 63. They look the same but o-ring #6 is 1.925x.103 and o-ring #63 is 1.862x.103. Use plenty of lubricant. Hope this helps.

Air leaking from the bottom of the gun (path of driver) indicates that cylinder seal orings are leaking (if without nails in gun the driver is slowly pushed down the cylinder when air is connected then cylinder seal is leaking ). Cylinder seal snaps on the top of the cylinder and should fit snug and have no cracks. Easy fix for cylinder ring. Remove head and pull out cylinder. Then remove the cylinder ring (part #n50015). Examine ring for cracks and replace as needed. Examine body of gun where spacer oring makes contact and sand fine scratches. Replace orings as needed. If air is leaking between body of the gun and nose casting, replace gaskets. Good luck.

Did you check to make sure the driver is not jambed with a nail? Look for flat spots on the O rings and sometimes rotate the piston 180 degrees. Load the piston edges at the O rings with gun oil. Last resort turn the gun upside down and smack cap on wood with no air plugged in then plug air to it. Gun should cycle after this. Old Framer with many guns.

The air leak can be one of a few things. FIrst make sure that you have added some pneumatic oil to the air stream. This will lubricate the o-rings and make a tight seal. If that fails to resolve it, repalce the o-rings. (kits available for around $20). Next, woul dbe the trigger assembly itself. These triggers wear over time and are easily replaced.

See the website below for parts and a good diagram of the construction of the gun. You should be able to replace the parts by following the diagrams.

http://www.ereplacementparts.com/bostitch-parts-c-29443.html?gclid=CO6tkb2y6KICFciA5QodOlL9xg

Please note that the exactmodel number is required to get hte correct diagram.

Hope this helps,
Dan

if you took the trigger apart the part that you unscrew has a nylon ball and a black rubber ring you should check them and make sure that you didn't loose them when you took it apart,if they are there, then you need to service the gun, and after you clean all the moving part and you put it back together, it may still leak from the top,Take a rubber hammer and give it a good hit,now not to hard, and it should seal

the top!! o-ring inside of thr top plate is bad you need to remove the plate /dissasemble and replace the o-ring

Air leaks from the bottom of nailers are due to leaking oring /s that seal cylinder to body of gun and/or leaking thru seal at top of cylinder where headvalve seats. Remove head and examine sealing surfaces of headvalve and top of cylinder. Must be smooth, then pull out cylinder and check oring/s that contact body of gun. Remove any fine scratches on inner body with fine paper (400 grit). Lube with silicone paste. Good Luck!

Take off the back cover and make sure it's not too dry inside. Spray the inside with some WD40. You can take off the top cover. Pop the piston, cylinder, and head valve out, making sure all the seals and rings are seated correctly.Sounds like the piston is momentarily sticking. Does it shoot at all? Lemme know. Please rate me

your problem is you have blown a seal. On some of the cheap chinese guns, it might be a flat gasket instead of an o ring.