FX Dreamline PowerPup broken valve

[EPG]

I had my .22 Dreamline Power Pup shooting like a “dream” at 39 ft/lbs with a 600mm barrel… certainly not a high power tune.

It shot a 198 17X (!) 40-Masters… then boom! It sounded like a rimfire as velocity went from 890 to 1009fps on the shot where the valve broke.

The rifle retained both tank pressure and plenum pressure.

I disassembled and found the valve stem broken.

Questions:

Is this common? This rifle has never shot slugs or been tuned above 40 ft/lbs with pellets.

Should I also replace the valve seat? Or should I expect it to seal properly with just a new valve…?

Thanks in advance for sharing your experience with Dreamline v2 valve…

-Ed

 

[NAProf]

I had my .22 Dreamline Power Pup shooting like a “dream” at 39 ft/lbs with a 600mm barrel… certainly not a high power tune.

It shot a 198 17X (!) 40-Masters… then boom! It sounded like a rimfire as velocity went from 890 to 1009fps on the shot where the valve broke.

The rifle retained both tank pressure and plenum pressure.

I disassembled and found the valve stem broken.

Questions:

Is this common? This rifle has never shot slugs or been tuned above 40 ft/lbs with pellets.

Should I also replace the valve seat? Or should I expect it to seal properly with just a new valve…?

Thanks in advance for sharing your experience with Dreamline v2 valve…

-Ed

View attachment 596081

Ed,
The interesting part of this is your photo showing the broken valve pin. The failure looks to be in the o-ring groove. Is that right? Can you describe the surface of the failed part - for instance; jagged, or like sandpaper, or like a cone shape? Maybe try to take a picture of the failure surface.

I am trying to determine if this was a fatigue failure or a one-time blow that snapped it. The reason is that the drilled hole in the block may have worn allowing the end of the pin to move a bit so it was struck by the hammer in a direction other than straight down the axis of the valve pin. I did a study many years ago on valve failures in the cylinder heads of the VW air-cooled engines used on the Type II, the Type III, and the Porche 914. The culprit was over heating which caused the valve guides to wear so that the valve didn't seat properly one time and the head snapped off on combustion.

Where I am going is that the problem may be the drilling in the block in which case you need a new block. If it is fatigue it might be a problem with the way that valve pin was heat treated and simply replacing the pin will be a solution. I doubt you need to replace the valve seat since the rifle sealed up with no leaks after the failure.
Cheers,
Greg

 

[Feinwerk]

I'm really surprised at that valve and design, if I understand it correctly. It appears that the sealing surface is the taper. Not sure why there is a delrin insert on the back side where what appears to be the valve return spring seats.

It looks like the hammer is impacting on the short side of that valve pin and oh my look how much that shaft is necked down by the o-ring groove!! As a part that experiences shock load when the hammer knocks this valve pin, that sends up red flags to me design-wise, as a failure point stress concentration due to a serious loss of cross-sectional area. If the inside corners of that o-ring groove are not very smoothly filleted, that will be the site of extreme stress concentration.

Maybe this is a balanced type valve design where there doesn't have to be a lot of impact stress to open it?

The back side pin that holds the return spring is extremely long. Check out the bushings and cavity that hold it and make sure that there's no way for it to bottom out on the back side and cause extreme compressive load during the shot cycle that might cause such failures or contribute to them. It seems to me that happened in another PCP design from a major manufacturer.

Feinwerk