Air Tank Dump
Just experienced air tank dump in my condor. Install Tony’s top-hat with the med insert shooting 18gr JSB and the gun shot beautiful. Decided to up the power with some 24.4 gr and some enjin 32gr so I took out the insert, turned up the power wheel to 8 and shot the heavier pellets. After about 7/8 shots the tank dumped. Turned it back down to 4 on the power wheel and was shooting 25.4 and it dumped again. Never had that experiance with the stock top hat. Maybe need a 0 ring behind Tony’ top hat?? I really don’t know what to do for sure. Did I damage something when it dumped the first time. After the dump the bolt was still closed but it marked a scratch where the bold cams over in the bolt lock slot.
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Dyotat,
Here are a few thoughts based on a computer model of Condor valve operation. I think what I’ve seen in the model pretty well matches your observations.
The model consists of the following parts:
Valve opening force and valve lift related to:
– hammer energy,
– hammer momentum,
– and elasticity of hammer to breech impact.
Valve closing force related to:
– pressure difference across the valve (tank to chamber pressure difference),
– valve spring force.
Valve retarding forces (oppose valve motion opening or closing) related to:
– valve and breech mass,
– clamp load of O ring seal on valve (valve to valve housing),
– clamp load of O ring seal on barrel (breech to barrel).
Based on these forces here’s what I’ve seen in the computer model:
The closing force from pressure difference reduces drastically when:
– the chamber is smaller (lower caliber chamber builds pressure rapidly),
– the pellet is very heavy (chamber pressure builds, but pellet doesn’t move much),
– the pellet or slug is very tight in the barel (chamber pressure builds, but pellet doesn’t move much).
The clamping force from O ring seals probably increases quite a bit with higher chamber pressures. (Need a better O ring model here…)
I think these line up with your observations that highly polished sealing surfaces, lubrication and harder O rings seem to help avoiding tank dump with heavier, tight fitting slugs.
The other finding from the model is that a very short, very large flow from tank to chamber makes most efficient use of air. This leads to high chamber pressures, which lead to valve lock/tank dump.
So the quest for best shot count bumps into the valve lock problem. I’m pretty suspicious of the O ring clamp being a key part of this. Has anyone looked at alternative sealing methods that would produce lower clamp loads?
The model is a somewhat large spreadsheet that emcompasses much of the physics in a gas gun. As always, I’d be happy to share the model with anyone who’s interested.
-x356b
No I haven,t lubed the base of the top hat. I have heard it both ways. Some say do and some say don’t. I shot again yesterday with the med restrictor for prob 100 shots and no problem. I will try lubing the TH put an 0 ring behind it, take out the restrictor and try it today. Thankyou………….gary
Did you lube the valve stem before installing?
Sounds like to much tophat gap for .22.
Valve opens past the point of return on lower pressure.
Had this problem with my .308. Took some time to figure it all out. If it was a .25 you wouldn’t have the problem. It is partially caused by the thicker barrel. .25 has the thinnest and .177 is the worst.
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Not sure if it’s the smaller caliber but it’s the fact that the barrel is the same OD with a smaller hole.
My .308 is a .428″ breech and .308″ hole. It took my awhile to figure out a valve setup.
I built a .25 with a .374″ breech and it never did work with a standard condor valve.
To get .25/.257 to work I had to modify my .308 valve and I have only had 1 dump and that was because of a breech I ring. My gun has never dumped and I can shoot down below 2000 psi with 74 gr slugs.