<<— What Happened???? An Airgun Valve Mystery —&a

Glad you are happy you’ve nailed down the problem and can proceed
And most important, you wern’t hurt 😯

I’ve worked with high pressure gases for years and as the saying goes-‘Familiararity can cause contempt’ (you do something enough times you start to lose that edge of caution…)
I’m always super careful to ensure anything going under pressure is clean and safe to be pressurised.

Goes to show even expert machinists like Mark can come up against unexpected and potentially lethal situations like this. Thanks to TAG,Mark and its members, this is important info that has got out to the masses…

GOOD WORK

You’re a smart kid dude. 😉

Paul, maybe. But in Mark’s case the burn was highly localized. Oil would be everywhere as a film and as a vapor/suspension but in Mark’s tank the combustion process was localized to the valve stem with the delrin piece, evidenced by the blue change in color of the stem. If the oil had been the fuel with an even distribution everywhere, you’d see everything burned lightly. In Mark’s case the fuel source was in one spot. If it had been nearer the aluminum, the tank would have failed at that pressure long before the combustion was complete and there would have been an explosion. Luckily the fuel source was threaded onto the steel valve stem and suspended away from the aluminum, the weak link. So even though the oxygen content is artificially elevated due to the very high pressures with a superrich environment, the temp was isolated just enough to keep the temper in the aluminum, but it was blind luck. A bigger valve stem/delrin and it would have been over as well.

Mark, I agree, the outsides may have cured and skinned over, stopping the curing process to the glue farther in, which remained liquid and uncured. The glue probably has a volatile carrier which normally flashes off, which remained on your stem. Wow, dude, that was too close. Do you need a threadlocker at all? I have little experience with valves, too busy fooling with other stuff, have built a few replacement delrin valve seats, but I can’t remember if I used a threadlocker or not. I’m glad you were able to figure it out. Now you can go shoot again. I’m sure you’ll be letting the glue cure outside the tanks for a few days before using them. Or switch to loctite? I’m not familiar with CA glue. Also, temper in tool steels is obtained at 400 F (at the low end of the scale), which is only twice the boiling point of water. I’m still a little iffy about your alum tank dude, although I don’t know the temper point of alum, never had to do that. But I do know of failures in aluminum 80 scuba tanks due to people repainting the tank, then putting into an autoshop paint booth for flash drying car paint jobs. That tank exploded the first time it was filled at the scuba shop and took off the legs of the employee filling it. I always err on the side of caution. If it were me, I’d cut that tank up and scrap it. I like my skin just where it currently resides, thankyou.

aloha,
walt

The plot thickens. Offhand, I would have said the culprit has to be in CF tank#2 or it’s line or the air in it but the problem did not manifest in the other gun you filled just prior to filling your gun for the last time.

No, I have not heard of other cases like this. But the vast majority of other shooters I know are running CO2, not pcp.

It cannot be the bore cleaner, as you fired it a number of times prior to filling. You refilled 4 times before the problem manifested. If the Hoppes was dieseling back into the tank you would have seen a problem on shot #1 with blown seals on the breech or a blown breech or a mushroomed barrel. You would have heard or felt something. If the Hoppes somehow got into your tank without combusting it should have caused a problem on the very first fill when the pressure differential was highest between your CF tank and the gun tank. So, sorry Riff, I’m not buying the bore cleaner explanation. There is just too much air hammering out of the valve and rushing down the barrel for a pressure wave strong enough to combat that kind of airflow to make it upstream without blowing the O ring seals and hammering the barrel.

I’m still curious about CF tank #2. Vent a small amount of the air from that tank and give it a sniff. Anything strange at all? Nothing volatile? This happened on the first fill from that tank. Check the fill line for any residue of any kind. Take samples from CF tank#1 and go back to tank#2 and back to tank#1. ANY difference in air smell? If you have your own compressor and air is free for you, dump the air in CF #2 just to be sure and take the valve off and check inside the tank with a flashlight. CHECK the bleeder. I am deathly afraid of mine. I made my own fill manifold in a brass body and after realizing how soft the brass was, and how much pressure it was holding back, now I wince every time I tighten that bleeder down. When I pressurize the system I stand to one side in case the bleeder threads let go. The bolt is going to fly out of there if the threads fail, just like a 4500psi gun would launch it. And that bleeder bolt is HEAVY and will cause serious dmg. I remade the manifold in steel.

We still don’t have the fuel source. I refuse to believe a sleeve of delrin will combust spontaneously when going from 2500psi to 4000psi, dust or no dust. I need to think some more.

You need to take your alum tank on the gun and look inside with a flashlight. We know for a fact the combustion happened in there. There will have to be some sort of residue… you mentioned you found something? what was it? the ash. Do you use a threadlocker on the delrin?? look for chemical interaction between delrin and loctite????

walt

Just spotted this thread and catching up. Crap, Mark, just reading this makes my skin crawl. That was pretty damn close. Someone watching over you that day. The screw was BLUE???

That there was some sort of combustion is a given. Ignition source could have been anything, but the fuel is a mystery. Riff’s scenario with the bore cleaner dieseling back makes sense, but I’m not 100% convinced. What was the time element and sequence? Was the bore cleaned before your shooting sesssion? How many shots? Over what time period? In order for the tank to retain the heat you felt at the last fill, the combustion event would have had to been close to when you actually detected the heat… within, say, 30 minutes or so. The seat failure would have been obvious and immediate. So, after your last shot of the day, you disconnected the tank and put it on your CF tank to fill? When you ran the pressure up, did you see the needle ‘skip’ when the valve cracked open? Or abnormal at that time indicating an empty tank? …all this to try to figure out if the valve had already failed when you tried to fill it or if the combustion event was after you filled/during the last fill.

Due to the heat possibly compromising the tank, I wouldn’t use that tank anymore. If the heat has annealed the aluminum, it may fail while at pressure. Or, have it hydro’d first to test it.

Was your CF tank warm after filling? Normally they cool down due to adiabatic change…

Trying to ignite silicon on your bench won’t work. In the tank under 4500psi the environment is completely different and the two systems don’t react the same way. You cannot replicate the explosion by looking for combustibility at 1 atmosphere.

walt