FX Leaking FX main valve and fix

Seems quite a few of their valves share this design. What appears to be a delrin seal ring on the outer edge of the valve sealing face. But the metal portion of the valve also overlaps with the valve seat sealing face which is entirely metal.

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Issue seems to arise after much shooting to where the brass retaining ring that appears to be pressed in behind the delrin seal becomes loose. Next with it is the seal it's self. Next thing you know your valve won't seal.

Just had to do this to my Ranchero. This valve is a spare stem and seat for my Crown. But they look near identical with the Ranchero one just being smaller.

Fix is simple enough. The valve lapping compound. Smear a tiny bit on the cone shape on the valve around where it seals. Have both the valve and seat removed from the gun. Press them together in the same way they would interface with eachother inside the gun and rub them against eachother in circular motions (normally I just spin the valve stem inbetween my thumb and index finger, holding the seat with my other hand, pressing them together) keep them as straight as you can. But I think some slight tilting and variation is good as well. Just try to be uniform about it. Doesn't take but a good minute or two to do the job.

Clean the compound off, reassemble and enjoy a leak free gun again. 👍

Fwiw, I did this to my crown as well a good while back, and havnt had any issues since.
 
So you are hearing a rattling in the body of the gun or a hiss in the barrel? Sorry, I’m just confused on why you’d look at the valve as the culprit.
When diagnosing a leak I like to take baby steps. checking one possibility at a time
The first (for me) is checking the valve.
Unlike gauges, fill nipples and other locations it is not static.
It is the most active part of the gun

Remove the moderator and the shroud, if you have them
Fill the gun
Close the bolt
Put a tightly fitting balloon over the barrel
And wait
If the balloon shows any signs of inflation no matter how minor, the valve is leaking
The wait could be seconds, minutes or hours (overnight) depending upon the severity of the leak

Hope this helps,@Patrick1
Edward