Advice needed for High power setup.
Hi guys,
Merry christmas to all on TAG.
I’ve started playing around with higher power settings in anticipation for my .22 barrel, my problem is I’m getting tank dumps. What I want to know is if I’m on the right path.
My setup consists of a new valve stem as suggested by Doug(Dyotat100) with three ports on the step. I haven’t measured the (one piece)tophat gap but its around .015 with a tiny o’ring under it. Driving all of this is a 103gr brass hammer. The PW was set too high but I only realized it a bit late-around 8/0. The rifle was filled to 2900psi.
I’m doing something wrong, either the hammer is too heavy or striking too hard. I’ve tried increasing the tension on the valve spring but if its too tight I’m getting that feeling of the spring crunching on itself.
Will it help if I make the hammer lighter or is there something less drastic that I can do?
Any help appreciated.
Nick
All Replies
Viewing 12 replies - 1 through 12 (of 12 total)
Your air output is far exceeding your input capacity. Add to that your hard to shift heavy pellets. Basically you’re opening a big door in a storm and having problems closing it again. I suspect once you up the calibre the dumps will stop. Until you do, have the valve spring as tight as possible, reduce the tp setting and use lighter/looser fitting pellets.
I use 304 stainless. Never had a problem. Only have had my first .308 fail because I drilled it wrong and new it would.
Thanx RC, I’ll need some luck.
Just for interest, what metal are the stems and tophats made of? Mine is made out of a section of a high tensile bolt.
My daughter and her BF are leaving for home today, they have 4 feet of snow and are supposed to get another 2 feet today.
I am hoping to get a break so I can take the air stripper off my Haley and try those RCBS bullets to tell if that is what is causing the tipping. I am sure it is, it is the only change I made and it was my most accurate bullet prior to the air stripper.
Good luck on yours Nick.
RC
No I just told him how to make a better one piece stem. Didn’t think it would cause tank dump.
He just needs to set the tophat gap smaller and go from where it works up to find the limits.
I had the same problem with .308. I have 2 valves I use. Tank 1 has .100″ tophat and the ports are just drilled with end mill and left alone. If it is potted I get tank dump. Second tank is .085″ tophat with same holes drilled but there ported and are triangle shaped.
If I run more tophat on tank 2, the shots get louder as fps falls and fps spread is more between shots. I was using that valve for the .257 with a different stem until I made another body for it. When I put it back to .308 I put wrong spacer in it and tophat was around .098″. Took me awhile to figure out what was going on.
I still have a few ideas to try out when I can find the time. My new .308 will be similar to the .257.
Heading to Redding right now. I have the .257 and .308 with me. If the weather wasn’t so bad I head up and visit you.
Is that your valve Doug, the one like mine?
RC
Thanx Doug. That gives me a good starting point.
Just something else I found out this morning, after topping up the rifle I fitted the new valve and got a dump. So it seems the new valve is the definitely part of the problem. So I’ll repolish it, I have had it in before and never had the problem.
Make sure the spring retainer is all the way in so spring is stiff as it can be.
Make your tophat gap .080″ with a spacer and then try .100″. .150″ is way to big. I have .130″ on my .25 valve and a light return spring. But the thickness of the barrel seems to play a big part of tank dump.
Same valve for my .25 won’t work on my .257 because I made the barrel .375″ instead of .309″. Tank dump. Best I could get it to do was 1000 psi for the first shot.
Somehow the .308 valve works with a smaller hole in the stem. I spent days making parts trying to get the the .257 working. I actually finally just gave up and moved on to something else for awhile.
Good luck
Thanx for the replies guys, I didn’t expect them so quick with it being Christmas.
I forgot to mention that the barrel is a std 5mm(.20) LW. Iwas shooting a 21gr Eunjin when I got the dump.
The hammer spring is also standard. The valve spring is pretty stiff, its also std-(.177/.20)
As far as I know the .22/.25 valve spring is a little softer.
@Dyotat-i’ll fit a plastic spacer to reduce to gap size.
With the reduced tophat spacing, will the 21gr pellet in a 5mm barrel cause the tank dump? My problem with the dumps is that I have to refill the Condor’s bottle with a Hill pump, so I’m trying to avoid dumps at all costs.
@RC-yes tankdumps will awaken the dead, I don’t think one will ever get used to it. Terrifying stuff!!
Merry Christmas
First thing is you need to put a hard spacer to limit the tophat to .100″.
Return spring will need to be stiffer also. What hammer spring are you using?
You will have better luck with .22 barrel and it would work fine on .25.
Funny thing about valve stem return spirngs Nick, if you take it out and you manage to air up your rifle again, it will operate without it.
You see with your 2900 PSI fill you have 2900 PSI pushing that valve shut.
So I would not tighten up on that spring.
100 grain hammer is not a problem either.
Perhaps all that air does not have a place to go with that little .177 bore so a combination of the heavy hammer, larger valve stem ports, and a tiny little .177 hole in your bore, it increases you valve dwell time and you get tank dump.
I think that until you get the 22 barrel so you have more outlet for that valve to empty into you will be getting tank dump.
You have also broken the most basic rule in that you have done two mods at once, it is always best to do them one at a time, but I bet 95% of us here have done many more than two mods at a time .
As a result, and the fact like most of us are like you and would want to play with that hammer and valve stem, put your original hammer back in use the new valve stem and see if that will stop the tank dump. If it still does it it is probably the bore being too small.
If it stops the tank dump, then put the heavy hammer back in and back all the way off the PW and see if it does the tank dump. If it still does, you know it is either the heavy hammer or the small bore.
Tank dump really wakes you up doesn’t it? 😛
Hope this helps Nick.
Merry Christmas to you and all here on the forum.
Roachcreek
Viewing 12 replies - 1 through 12 (of 12 total)
- You must be logged in to reply to this topic.
Thanx Pablo, that makes a lot of sense. So far I’ve tightened the valve spring as tight as possible, also removed the o’ring under the tophat. HUGE difference, she’s back to her old self again with plenty effortless power. When I’m back home I’ll fit a much thinner o’ring just to protect the tophat and valve face. Consistency is what it should be again.
Much appreciated guys. Thanx and happy new year.