Fx Impact problem. Please help ...

My friend have a problem with his FX Impact. He was asking me to help but I couldn’t because I don’t have any experience on Fx Impact. I also have never owned a Fx Impact. 
His Impact was working good at max power wheel with regulator was set to 125 bar. He was trying to take the cylinder off. After that, the gun was cocked and fired one without cylinder. It was super loud when the gun was fired, and he also heard the air was coming out. He took the valve stem housing off to check (he didn’t touch hammer or regulator) and then he put everything back because nothing wrong was found. However, after he put the cylinder back, the air came all the way through the barrel. He have never known what’s happened. Was it leaked or broken something? Does anyone know what’s happened and how to fix this?
Thank you
Kenny,
 
"Dirte"If I understand correctly....If the gun was shot with low or no pressure on it. A. valve can be boogered up and not seating against the valve seat. B. Valve seat can crack under the o'ring area. Both will let all the air out of the barrel and not build pressure.
Hynzie said:
this wont work with a hand pump if you got a tank ,,give the gun a large blast of air quickly this may seat the valve properly HYNZIE

Thank you guys ... I will let my friend know, so he can try ...