M3 Air Leak Out Barrel

[jbravo103]

I woke up Sunday morning to find my M3 completely empty of air. All regs at zero. I tried refilling but air just flows out the barrel. Any ideas? I also noticed the valve pin is not sitting flush with the valve body (see pic below). This doesn’t seem right.

 

[Ries]

Valve is not seating properly, it should be flush

 

[rappert]

I would try hooking up your air compressor again to the gun and while it is pumping pull your cocking lever back to see if your valve seats and seals. If it does your leak may be elsewhere. I have had air come out the barrel after I tried to refill after completely degassing my gun. Cycling the cocking lever has always re-sealed it. I have only had it happen on a completely empty gun.

 

[jbravo103]

What’s odd is that my gun was just sitting on the shelf with 150 bar in the plenum one day and then 0 bar the next. Seems odd that the poppet valve would just unseal itself for no reason.
I took my gun apart last night and looked at the valve seal and valve seat. Visually they appear in perfect condition. I then checked the o-rings on the valve housing and they look brand new. No dings, dents, tears, scratches. I’ll replace the o-rings just in case but doubt they were the culprit.

 

[rappert]

The valve poppet didn't unseal itself for no reason. It probably is not the cause of the leak in the gun but the effect caused by the real leak (which I believe is elsewhere). If you have a leak somewhere else in the gun and the gun totally degasses overnight, during that degassing process the valve poppet may open up when the pressure gets below a certain level. It happens on a perfectly sealed gun sometimes when you remove the bottle from the gun. That's why I suggested hooking the gun back up to your compressor and cycling your charge handle on the gun while pumping on it. This should seat the valve. Once it is sealed you can pump the gun up a bit and use leak detector spray to find the real leak, or it may be loud enough to hear.

 

[jbravo103]

rapper,
I think you are spot on regarding the valve seal. Once pressure in the plenum gets below a certain point the valve seal can start leaking and degassing will occur rapidly.

I partially reassembled my gun last night and pressure tested at 110 bar. No audible leaks and gun seems to be holding air. I checked again this morning and manometer readings were still the same. I have not replaced any parts or o-rings yet.