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PostPosted: Tue Dec 30, 2014 4:36 pm 
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I was just wondering if this design for a valve would work. The idea being, the hammer strike would require less force to open the valve,because of the lever action, there by needing a lighter spring and ultimately a lighter trigger pull. The leverage that aids the opening of the valve, also aids in closing it. so, a lighter spring also could be used inside the valve. Having the valve seat at the transfer port, puts the out going air closer to the pellet. I hope the picture can be understood. I'm not an architect by any measure. This question, of course is directed at the air gun guru,s out there.
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PostPosted: Tue Dec 30, 2014 7:53 pm 
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Couple of things I noticed.... Looks like you have an O-ring to seal the stem when closed, but in the striking position I don't think it would seal as shown.... Also, you don't have enough room for decent mounting screws for the valve.... Could maybe put a backer block behind it to take the end load....

As to the valve itself, it doesn't have much travel and is quite small, so the flow would be limited.... Depending on the material, it may be problematic getting a tilting valve to seal at those pressures.... About all you can do it build it and see....

Bob

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PostPosted: Tue Dec 30, 2014 8:15 pm 
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Thanks for the input Bob. The valve would be the same as a regular disco valve with 3 retaining screws. I didn't do a great job of drawing them in. As for the stem. All 2240 valves have no o ring at all. So there must be some blowbye anyway when open. I was thinking that air pressure and spring pressure would be adequate to seal the valve while closed. As for adequate travel, the only solution might be a larger TP.
And as for building one. I have no means or skill for such build. I was hoping someone with the skills and machinery and some knowledge of air pressures and their affects , could modify the idea to make a more efficient valve. Your project gun is what got me thinking about current valve setups, where it takes such a heavy hammer spring to get the power your looking for..

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PostPosted: Tue Dec 30, 2014 9:00 pm 
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Current experimenting seems to be going in the direction of balanced valves, with a piston in the middle of the valve stem, c/w O-rings, that counteracts the closing force on the poppet, cancelling out all but the area of the valve stem itself.... This can remove about 70% of the force needed to open the valve, but they are beyond my ability to machine.... so I'll have to wait for somebody to produce an affordable and tuneable version.... ATM, tuning them seems to be the trick, so far they are pretty much all prototypes, with one exception....

Cothran is selling a "force reduction valve" that can work in big bores up to 45 cal in a Disco without resorting to Mondo hammer springs, apparently.... but I have NO idea how they work.... and have never seen one.... There are, of course, no photos of the insides available....

Bob

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PostPosted: Wed Dec 31, 2014 8:12 am 
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Yes the balanced valve would greatly reduce the need for a heavy hammer strike. Especially if an adequate seal could be obtained with delrin or nylon, which wouldn't stick to the inside of the valve body like o rings do.
I'm looking forward to seeing the final product.

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PostPosted: Wed Dec 31, 2014 10:41 am 
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be easier to have the hammer it a lever which transfer to the regular valve pin . . insted of trying to put a sealed lever inside .


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PostPosted: Wed Dec 31, 2014 11:32 pm 
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rsterne wrote:
There are, of course, no photos of the insides available....


http://www.cothranmachine.com/PowerHous ... 202013.pdf


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PostPosted: Thu Jan 01, 2015 12:27 am 
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Thanks Al. I couldnt find it in my file folder so you beat me to it.

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PostPosted: Thu Jan 01, 2015 12:54 am 
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Thanks for that Al, at least we know what the parts look like.... I still have no clue how it works, however.... :mrgreen:

Bob

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PostPosted: Thu Jan 01, 2015 1:53 am 
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A brief description of the function is in the article Bob. :wink:


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PostPosted: Thu Jan 01, 2015 7:51 am 
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Interesting. Not enough description in the article for me to figure it out.


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PostPosted: Thu Jan 01, 2015 11:29 am 
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Glad I'm not the only one.... :roll:

Al always seems to be able to figure out how these things work at a glance, not me.... :(

Bob

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Airsonal;
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Proud Member of the 2000+fps Club!


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PostPosted: Thu Jan 01, 2015 12:19 pm 
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Figuring out how something works by looking at it is how I earned my bread for 25+yrs...sometimes I take that for granted.

A lot of double speak, bs and odd terminology in the article, but will do my best to be clear...

Very small hole in the valve stem is a vent...(can just be seen below and to the left of center of the o-ring) stem is partially hollow. Small piece of rod slides inside of valve stem.

Piston assembly on the right is secured to the body by the screw.

Valve "hat" is hollow...slides over top of piston assembly...uses the urethane seal shown...lower force holding valve closed requires softer material to seal.

The piston area being vented to atmosphere, the net effect is a reduction in surface area for pressure within the valve to push on...resulting in lower opening force.

During the shot cycle, pressure bleeds through the hole in the valve stem, past the rod to the piston assembly and adds a considerable amount of closing force. Once shot cycle is completed, this would then vent back to atmosphere...rod would slow the venting, helping hold the valve closed during early (higher force) hammer bounce events. Rod diameter could be tweaked to adjust fill rate/closing force, but would also effect on the venting end...

HTH,

Al


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PostPosted: Thu Jan 01, 2015 12:50 pm 
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Al, thanks for that explanation, I am starting to understand (I think).... You certainly have a knack for reverse-engineering....

So the force on the seal, from the top hat, is the spring, plus the pressure on the area of the seal minus the area of the small O-ring that is mounted on the front piston, which is solidly mounted to the front of the valve.... ie area of seal OD minus area of top hat ID ?.... The amount of "force reduction" on opening is equal to the area of the front piston times the pressure.... I think I understand that for the first opening cycle (now)....

Still trying to figure out the "anti-bounce" part, partly because I can't see the hole in the stem and don't understand the venting path.... I assume the valve lift is limited by the length of the rod ("stabilizer piston") when the valve stem drives it against the force reduction piston?....

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: Thu Jan 01, 2015 1:28 pm 
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rsterne wrote:
Still trying to figure out the "anti-bounce" part, partly because I can't see the hole in the stem and don't understand the venting path....

Using my laptop with a touch screen to blow up the picture...only way I can make out the hole in the stem...Knowing to look for one certainly helps. :) If you were to pressurize the piston assembly area, you create closing force...controlling the bleed down of that pressure (using the rod) will allow that force to remain in effect for a longer period of time...rod acts like a leaky check valve.

I assume the valve lift is limited by the length of the rod ("stabilizer piston") when the valve stem drives it against the force reduction piston?....

Just eyeballing it and without knowing the actual depth of the bore in the valve stem, I would say that it looks as though the bore is deeper than the piece of rod...likely valve stem assembly could travel up to the piston assembly, but doubtful that it actually would...think you might know someone who did some testing on valve opening? :wink: .

Bob


Clear like mud? :)


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