FX IMPACT - VALVE STEM STICKING - HELP NEEDED.

[Avidrob]

Hopefully mr Rowe can help. As im going insane trying to fix this.



I have a strange problem with my valve stem. I think it might be the valve tube quad/oring binding under pressure . Let me explain symptoms.



From a fresh fill i get 10-20 ish shots at 880 fps, then the velocity sudendly drops over 5 shots. 750. 720 550, 430, then 0. The valve stem wont open.

If i remove tank and release all the plenumn volume presure then recharge its works again but only for 10-20 shots.

Its almost like the reg presure has gone higher than the hammer can open, but Reg presure is 135 and does not change. Huma reg. 

Iv checked the valve and hammer seat to make sure they havent unthreaded. Iv fully stripped and rebuilt the impact 20 times now, can find anything obvious.

Valve stem moves free and smooth when in bits on the work bench.

Only thing i havnt tried is changing the oring in the valve tube that seals the stem. Wondered if it could bind up under presure?



Please help.

 

[AirSupply]

Have you checked the hammerseat is home and tight. Part number C1. If this backs out it can stop the valve opening. 

 

[bandg]

"Have you checked the hammerseat is home and tight. Part number C1. If this backs out it can stop the valve opening. "



I don't have an impact so forgive the uninformed question but would that relate to the normal function for a few shots after releasing the plenum volume? Sure sounds strange.

 

[Avidrob]

Airsupply.

Yep home and loctited.

That was my first guess but sadly its not the problem.

Its very strange

 

[Avidrob]

Could it be symptomatic of a cracked valve seat? I know this is a common problem. The stem is flush with the back of the valve body, and the seat surface looks clean.

I havnt removed it but looking at it as fixed in the valve body it looks fine

 

[heavy-impact]

Someone else had the same problem a couple of months ago but I can't remember the user name.

 

[AirSupply]

I just doubt it’s the x ring and the valve seat has been rebuilt so it really only leaves that end of the valve rod. The hammerseat can sometimes strip the tread and move around a bit. It works it’s way forward and then locks the rod. 

 

[Avidrob]

Someone else had the same problem a couple of months ago but I can't remember the user name.

I think i saw that post, but i belive his problem was a unthreaded hammer seat. My hammer seat is fine.

 

[Airgun-hobbyist]

Did you try removing and cleaning the regulator? From what you are saying, it goes down to zero pressure. That is pressure after the regulator that is missing, going down to 0 psi after so many shots. The regulator sounds like it is locked up so it won't let in more air until the pressurised bottle is removed, allowing the regulator to settle or release.

 

[Avidrob]

I just doubt it’s the x ring and the valve seat has been rebuilt so it really only leaves that end of the valve rod. The hammerseat can sometimes strip the tread and move around a bit. It works it’s way forward and then locks the rod.

My valve seat hasnt been rebuilt. Iv removed the valve body and the seat looks ok but i havnt removed the seat from the valve body yet.

Its definatly not the hammer seat its been checked and rechecked.

I might order a new valve stem and valve seat, see if that does anything.

 

[Avidrob]

Did you try removing and cleaning the regulator? From what you are saying, it goes down to zero pressure. That is pressure after the regulator that is missing, going down to 0 psi after so many shots. The regulator sounds like it is locked up so it won't let in more air until the pressurised bottle is removed, allowing the regulator to settle or release.

The reg pressure from the guage never moves. Its bang on 135. 

If i depresurise the plenumn slowly the hammer will eventualy break the valve open at around 35 bar.

I can then represurise it works ok for a few shots the jams up again.

Somthing is making the valve or valve stem bind / stick. But only under pressure.

 

[Airgun-hobbyist]

Did you try removing and cleaning the regulator? From what you are saying, it goes down to zero pressure. That is pressure after the regulator that is missing, going down to 0 psi after so many shots. The regulator sounds like it is locked up so it won't let in more air until the pressurised bottle is removed, allowing the regulator to settle or release.

The reg pressure from the guage never moves. Its bang on 135. 

If i depresurise the plenumn slowly the hammer will eventualy break the valve open at around 35 bar.

I can then represurise it works ok for a few shots the jams up again.

Somthing is making the valve or valve stem bind / stick. But only under pressure.

I see what you meant now. Maybe the screw on the dial worked itself loose, causing the hammer and spring preload to change off of whatever the dial is set at. This would explain why the hammer can't open the valve.

 

[AirSupply]

I just doubt it’s the x ring and the valve seat has been rebuilt so it really only leaves that end of the valve rod. The hammerseat can sometimes strip the tread and move around a bit. It works it’s way forward and then locks the rod.

My valve seat hasnt been rebuilt. Iv removed the valve body and the seat looks ok but i havnt removed the seat from the valve body yet.

Its definatly not the hammer seat its been checked and rechecked.

I might order a new valve stem and valve seat, see if that does anything.

I think that’s a good idea. Just a heads up you might be interested in the fact fx is bringing out an upgrade kit with the larger plenum and bits and pieces (Mk11). Not sure what exactly it consists of but may be a bigger valve seat. Might be worth asking about it as you may get the pieces you want and upgrade as well. 

 

[Avidrob]

So just removed the valve seat to inspect, its fine, no splits. Im still thinking about that ring on the valvetube / valvec stem, i cant think of anything else. Short of the valve mushrooming under pressure and getting stuck

 

[Zandak]

Hi, I am having similar problems with my impact, did you reach any conclusion?