Originally Posted by hmangphilly
I attached a snap on cylinder leakage tester EEPV309A00 to the muzzle,
air cylinder fitted but only filled to 30 bar
hammer cocked then released against dry fire switch
join tester to air line
adjust the leak tester to 100psi
of course this is a steady 100 psi rather than a sharp blast of 80 odd bar so at this pressure the air has plenty of time to find its way down the stem .
I'm sure the leakage doesn't scale up to any where near 35psi during firing
but you could really hear it quite clearly coming out of the safety hole.
and it does show that there is an appreciable blow by down the stem
if this was a motor I had rebuilt it would be coming apart again without doubt.
i'll see if I can do some pics if you cant picture this test....worth a 1000 words and all that
Don't forget that you still have possible leakage past the probe seal (which rarely seal perfectly) plus the two barrel seals which from the factory are often sliced upon assembly.
How were you ensuring the firing valve was open?? was it open to the same extent & time as a fired shot
If you wanted to find out the exact amount of air lost via the valve stem on a particular rifle then you need to have a gauge fitted behind the valve stem & fire an actual shot...not sure how the hammer is going to hit the valve though?
I think realisically small losses of air are something you just live with as imagine the problems you would create by trying to fully seal the valve stem.