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Old 01-25-2011, 02:15 PM   #411 (permalink)
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COSMOS doesnt come stock with solidworks? I guess I'm spoiled.
they call it simulation now and a low budget version does come standard but I thought the high dollar version could do flow, I'm not finding how though.
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Old 01-25-2011, 02:17 PM   #412 (permalink)
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Just a thought on testing whether some air does in fact slip past the powertube and is wasted behind the bolt. Can a CCI breech be drilled and tapped for a pressure gauge? Maybe epoxy it into place if there's not enough to cut into?

Another idea that would make testing easier is separating the 12g changer from the gun and putting it on a scale accurate to 0.01g. Should make testing all variables easier without the need of firing an entire 12g for each set. For example one can shoot 10 balls, find the difference in weight, and extrapolate the efficiency.
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Old 01-25-2011, 04:08 PM   #413 (permalink)
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Originally Posted by REDNA View Post
ok so impact of the hammer is not the issue it is the slamming shut of the valve.

thanks E.
Yep, thanks my man.
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Old 01-25-2011, 04:20 PM   #414 (permalink)
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sorry, I modeled a trraser valve last night so I could check the flow today but our package doesn't appear to have flow dynamics like I thought it did. I am amaized at how little of the port actually extends past the end of the valve seat. Must cut 70% of the potential flow.
We could probably increase dwell by about the thickness of a nickle.

With that washer in place, I can still successfully cock it. So the stop can be moved forward, and the ports/dwell will be extended further.
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THE-SHOOTIST Anyone chubbin' like me for this?
mailmanmike Since Monday! That's more than 4 hours though, so according to those cialis ads I should see my doctor.
tlane77 I think for a non-chemical chubby it's 6 hours before its time to see a doctor. So you should be good for another couple hours.
splattttttt I wasn't goin to google "chubbin" because I assumed it had to do with fat. The lard type, not the fun stuff. But what ever feelings Jeff's experiencing, then they must be of the fun like stuff...
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Old 01-25-2011, 06:12 PM   #415 (permalink)
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I did some quick and dirty math- it appears 'perfect' efficiency will get up to around 75 shots per 12g, as for 12g of an ideal gas with CO2's weight, it would be 89 shots (unless i totally screwed that up- very possible).

That said, I'm just recalling my engineering fluids class- 'major' losses were momentum shifts, 'minor' losses were friction and turbulence. It makes me wonder if there's a way to get rid of the direction changes at the powertube end, and at the bolt tip. A gradually outward-tapering bolt face (as popular on Snipers), and any way to get a straight path into the power tube instead of creeping sideways around that cupseal might be two huge areas for improvement. Even boring the valve body wider right near the valve seat, so there's more volume along the axis of the ports (in the perpendicular direction) than in the longitudinal direction, so the air goes from radial flow to axial flow (chamber into ports, ports down powertube) instead of axial to radial to axial (back of valve body, near ports, in ports, down powertube) might offer significant improvement.

I got fed up with the whole hammer assembly and my only redesign I've considered worthwhile so far involved a complete replacement of everything behind the bolt. It's not even a Nelson anymore, just fits neatly in the same breech. The powertube really is impotent.
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Old 01-25-2011, 07:07 PM   #416 (permalink)
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Fly.. I agree with your fluids assessment as to losses. I'm holding a kid in one arm and was supposed to read a book to the other 5 minutes ago.. so I'll get back to you later with my thoughts.

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Old 01-25-2011, 07:08 PM   #417 (permalink)
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Yay, someone else who knows fluids agrees with me that the valve chamber should be made short and fat rather than long and skinny.
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Old 01-25-2011, 08:05 PM   #418 (permalink)
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I've thought that for a while, that's what prompted the statement about different means of devolumizing earlier. I really like the relative dimensioning of a Nova dump chamber, I bet a similar valve type - like in the open source gun - could get ridiculous efficiency if it could get the necessary volume in that ratio and closeness to the ball.
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Old 01-25-2011, 08:09 PM   #419 (permalink)
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Actually leafy.. no. The transition from the valve chamber then back to a restriction wastes energy (more so with liquid than gas)... especially for something as slow as a pump gun... it really doesn't matter to have a BIG valve chamber. The more constant the path volume the better.

Jack.. that is awesome that you were able to show that!!!! That gives me faith that the LP option could work.. as you know my fear was having to significantly design the "drive" train downstream of the valve.

I need to digest the rest of what was said.. damn cold is slowing down my brain.

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Old 01-26-2011, 03:46 AM   #420 (permalink)
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the math... areas of ports and PT outlet tubes

Ok so I wanted to do the math to figure out the best porting for the PT.
First I looked at a stock Phantom PT.
Id of PT tube 0.172dia = 0.086R A= 3.14 (rxr) so A= 0.0232234 cuin.
Stock Phantom PT port holes 0.080dia A= 0.005024 per hole X3 = 0.015072cuin total area
This means that the ports are only 64% of the outlet or restrict 36% of the flow.
The PT only needs to move 0.15 to get its full flow capibilities.
Moving the PT further back will lenghten the dwell and will dump more total gass behind the ball but flow does not get better, faster or more efficent.
The narrowest part between the holes was 0.122 on a stock PT (called "post" later)

So I measured the OD of the port end of the new PT.
0.348dia C=3.14 X Dia so... C=1.092272
I need 3 post at 0.12 wide leaving 0.73272 of C for holes / 3 = 0.244 dia per hole
0.244 dia = 0.122R A= 0.0467357 cuin per hole x3 = 0.1402071 cuin total area
Now if the new PT only travels 0.15 back like a stock Phantom then the area exposed would = 0.0701 cuin for the ports (actually it's a hair more)
Since the port area is so much greater than the outlet. The PT only needs to move a fraction the distance of a stock Phantom PT to get full flow. Dwell time requirements drop meaning lighter hammers and main springs.
The PT outlet opening is 0.234 dia so A= 0.04298346
Comparing the PT outlets openings the new tube is 184% bigger than a stock Phantom, just shy of double.
When you factor in the flow restrictions of the stock Phantom PT's ports the new PT will have 286% better flow or almost triple the flow capabilities.

There may be other bottle necks in the system but it will not be the PT porting.

So on paper the new valve should be an improvement. Just need to prove it in the real world.
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