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PostPosted: Fri Oct 04, 2013 4:05 pm 
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Does anyone use a Delrin poppet, or brass for that matter, with a piercing pin?
I've seen posts talking about delrin flowing at hipac 3k psi levels, and am after a reliable replacement.

I do not wish to give up the C02 cart ability of my gun though, so a disco valve poppet won't do it.
Is there a stock source for a brass or other material poppet with integrated piercing pin or can someone reading this whip one up?


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PostPosted: Fri Oct 04, 2013 4:58 pm 
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Location: England.
Poppet? You mean a knock open valve seal.
Yes been making them that way for 20 odd years, no problems if made right.
One in here next to yellow return spring http://pic20.picturetrail.com/VOL15/728 ... 294937.jpg

Can be like this and better off junked http://i1140.photobucket.com/albums/n563/Jonhareng/Shooting%20choice%20of%20champions/WelhamS2Powermod.jpg

No idea what you mean by 'piercing pin'


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PostPosted: Fri Oct 04, 2013 6:09 pm 
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Location: Alberta Canada
Believe he is speaking of a 22xx series valve stem with CO2 piercing pin.

Sorry only know of delrin seal for hpa, no piercing pin to accomodate CO2 caplets as well.

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PostPosted: Fri Oct 04, 2013 9:12 pm 
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Can the machinists among us offer comments on brass/aluminum, brass/brass, aluminum/brass sealing?
I really don't have high expectations I could make something functional on a drill press...

I've seen brass/brass, but even those had a flexible sealing surface with likely all the failings of a stock 2240 valve poppet seal when pushed too high a pressure.
Maybe all that is needed is a retrofit stem and a through hole in delrin the diameter of a piercing pin?


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PostPosted: Fri Oct 04, 2013 10:08 pm 
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If you want to use hpa than a Delrin valve stem is what you want. If you want to use CO2 WITH THE PIERCING PIN TRY TEFLON. Cant have it both ways.


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PostPosted: Fri Oct 04, 2013 10:35 pm 
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While I appreciate the assertive opinion, could you offer some explanation why one cannot have both Delrin and a piercing pin?
The stem is steel (I think) so replacing it with an extended stem, shouldered at the same depth as stock but extending in diminished diameter seems a reasonable method to retain both delrin for hpa and a pin to pop a cart open.

Bob's reference to flowing delrin with noteable caveat that throat width was modified.
http://www.airgunforum.ca/forums/post368039.html?hilit=delrin%20flowing#p368039


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PostPosted: Sat Oct 05, 2013 8:15 am 
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The problem I had with Delrin flowing was on a very large valve throat area, and hence large forces (>300 lbs. opening force).... If you put a Delrin sleeve on a long steel pin as the poppet head, you will have the additional problem of sealing the Delrin around the stem (piercing pin)....

Tuning a gun to work on 3000 psi and also at 850 psi is not possible (in my experience) without significant change to the hammer spring because of the nearly fourfold change in force required to open the valve.... The spring supplied to allow the HiPac to work at 3000 psi makes the gun VERY hard to cock from all accounts I have read....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Oct 05, 2013 9:27 am 
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Thanks for contributing Bob.
The link to your hyabusa build shows a disco poppet with a hollow delrin seal - did this show signs of leakage?

If not, extending that stem in the form of a pointed piercer for carts should not add any additional sealing issue.
I do concede that tuning for both is not anywhere near ideal and looking for trouble in performance curves for sure.
I would love to be able to tune for sub PAL with a cart for backyard plinking and hipac up for hunting, even if it means reducing the upper pressures for the best compromise. Perhaps limiting to the 2k spring with additional preload from an adjuster.

We must dare to dream at least.


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PostPosted: Sat Oct 05, 2013 9:45 am 
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Disco Poppets are "overmolded" which means the Delrin is formed hot (cast?) over the stem in a mold.... The steel stem has a 3/8" diameter part INSIDE the Delrin head, with the plastic cast (formed/molded) completely around it (ie the stem is "T" shaped, simply covered in Delrin).... The earlier stems did not have the hole, the new ones do.... I haven't seen any difference in their performance or sealing.... I assume the Delrin being molded right onto the T-shaped stem prevents any leakage down the stem.... My theory that it was part of the problem in the Hayabusa turned out to not be the case, as the second poppet (no hole, and with the metal band on the outside) proved.... The Delrin itself was flowing/extruding into the large valve throat....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Oct 05, 2013 1:51 pm 
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I assumed overmoulded but knowing there is more than a stem shoulder at work inside for support is important info.
I will have to shelve the dual use until I have extra bits to try a cart pin retrofit to a delrin disco poppet.
I reckon it can be done but maybe the tuning issues may not make the task worthy anyway.

I always found that the smaller the pierced hole, the more economic the shots on a cart, given sufficient delay between them so a needle might do it for me and not get tossed out of the other end of the poppet on hammer strike. We shall see.

Thanks for the comments.


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PostPosted: Sat Oct 05, 2013 2:33 pm 
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The small pierced hole may be indicative of a lighter hammer strike (eg. less spring preload).... which in itself would result in less CO2 usage.... ie the smaller piercing hole may be a symptom, not a cause....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sat Oct 05, 2013 4:27 pm 
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Yep, thanks Bob.
RVA was dialled out at the time, but has become practice now as fps was more consistent and less C02 and noise was result.
That, and I may have failed to tighten C02 cap as much as previous.

Stop learning and I'm dead.


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PostPosted: Sun Oct 06, 2013 8:57 am 
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I have reduced hammer strike to the point that the cartridge took several hits to pierce.... The result was a gun that sipped CO2 and the velocity was nearly constant over a wide range of temperatures.... The valve was "self-regulating" just like in a PCP where higher temperature increased the pressure, the valve didn't open as far, and the velocity didn't increase.... At low temperatures, the reverse occurred, the pressure dropped, the valve opened further, and the velocity didn't drop.... With care, I was able to achieve virtually constant velocity from 5*C to over 25*C.... and up to 130 shots per cartridge in .177 at just under 500 fps.... That made it cheaper to shoot than a .22 cal. springer....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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