Air Arms AA S510 AIR LEAK

[MartinUsher4]

A question for the experts, I have an Air Arms S510 Ultra Sporter XS Regulated that sprang a leak after shooting a few rounds off.
the leak came from the hole in the cylinder where the regulator housing lines up inside.
Sourced a set of replacement seals/rings and stripped to service.
replaced the backup ring and 23x2.5 -90 rings on the firing valve body, also the two 15x2-90's on the regulator having been directed to do so.
reassembled and tried filling, when getting to 50 or so bar the leak slowly came back again, managed to get to 100 bar and it settled down and sealed.
took a shot and the air blew out of the hole again, then settled to seal, each time shot the same result.

anyone got any ideas of why the leak blows and slows to a stop/seal, and where i should look next?
could it be the regulator not fully sealing, i am at a loss right now.
any help greatly appreciated.
regards,
Martin.

 

[nervoustrig]

Possibilities that come to mind:

1. Damaged O-ring – When the piston cycles, the O-rings break free momentarily and then have to resettle. If a small bite is taken out of one of the O-rings, it may leak for a short time until the elastomer has some time to cold flow, so to speak, and re-seal against its mating surface.
2. Hardened O-ring – Same principle as #1. This is an O-ring aging symptom so it’s not relevant if you replaced all the O-rings, but some regulators have an O-ring in an internal groove that’s easy to miss if you don’t know it’s there.
3. Scratched sealing surface - With the aid of magnification and good lighting, check the bores where each the small end and large end of the piston goes. A defect in one of these areas can produce the “leaks then seals” symptom.

[edit] On re-reading your post, the large-ish O-ring sizes you described sound like ones that seal the regulator body. The sizes for a regulator’s piston are usually smaller, and these are the ones that cause a leak from the atmospheric vent.

 

[Motorhead]

Vent hole leaks ( Regulated PCP's ) more times than not can be traced to the regulators inner "Spool" o-rings failing.
Yup Rebuild the regulator time.

 

[nervoustrig]

Just FYI the part I referred to as the piston and Scott referred to as the spool is the brass part on the left side of this picture

 

[MartinUsher4]

Thank you for the responses guys, i did replace the o-rings on the reg body as well as the firing valve body.i have not replaced the reg or seals within yet, figured it would be just as well to replace the reg itself.

i will look at the surfaces again with a scope but did not see anything foul on first inspection.

thanks
Martin.