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Thread: Airflow: Is more ever too much?

  1. #51
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    Am trying to see how a heavier spring yields lower operating pressure. I get the lower sweet spot with a higher flowing system, and get the closing force issues, and would agree that a heavy valve spring is better for closing because it's both quicker and also isn't susceptible to pressure fluctuations. But I don't see how, by itself, a heavier spring would allow for lower operating pressure. As I see it, a heavier valve spring, all things equal, only means a heavier hammer spring to knock it open for the same effect.
    To get back to this (sorry - jumping in an out of a few things here) - the sweet spot is independent of the velocity - it really is just a curve. Say the sweet spot is 200psi on one gun. Your velocity is going to be higher at 200psi with the same hammer spring tension than if your gun was sweet spotted to 180psi. You are just finding a point of balance between valve flow and back pressure effects. If you want to run lower pressure, then run a heavier valve spring. A heavier valve spring will also increase your efficiency. BUT - if you were not adjusting the hammer spring, this velocity will go down. So you tick up the hammer a bit (nominally a small bit, the hammer tension is a couple ounces to a lb difference and we are talking pounds of back pressure.)

    But some where in there your hammer spring will have too much tension at full extension, and that will affect the valve, holding it open longer than you want. Decreasing efficiency. Add to that the hammer tension will also affect the LPR setting - and hence, the kick and feel of the marker.

    There are quite a few factors to balance.

    Interestingly one of the most consistent and efficient cockers I have built was running at 600-800psi, where the curve goes back up.

    Post volume, pre-ball capacitance effects?

    Paging PBSteve re: Chasing the Dragon (Inside Paragon dev joke)

    Yea, it modulates the effective flow through the valve because is changes the dP across the orifice. Consider that if you had a valve with infinite flow and infinitely fast closing speed (e.g. an idealized Paragon valve) and a ball with a perfect seal, you'd be able to change the ball acceleration profile only by the P*V energy of the slug of pneumatic energy you placed behind the ball. That slug would then fully expand in almost a batchwise process, and you'd theoretically have yourself something very efficient...
    YEARS ago, late 90's? Early 2000's? I CADed up a large number of guns, and found an interesting figure - if I build a solid mass of the entire internals; valve chamber, bolt, body sections, and 6 or 8" of barrel - I could take the energy they nominally used per cycle and average it across the entire volume mass and get 50psi. This wasn't so easy to get from most poppet units, but was consistent on the spoolers. Even chased it in some of my initial prototypes because they ran 50psi off of my first calculations. The last 50psi was wasted (then) in most guns.

    I had remembered an article in APG about breech chamber pressure. Forgot who wrote it. They said the breech pressure (at the ball) should be 50 to 90psi. Over 90psi, the ball would break paint. Under 50psi and the ball would lose too much energy to effectively leave the barrel with any efficiency. So total open volume valve to ball is an issue. Have a long bolt, like the spyder, and you lose some efficiency. The cocker has a fairly close coupling from valve to ball.

    And as a final bit of interesting:

    On the Raceguns, with a well sprung setup (stock even) at 7ms of dwell I could get consistent 'vacuum' affects, where the tissue paper would be sucked into the breech. At 8ms it would happen, 9 ms nothing. At 6ms nothing, and 5ms sometimes a bit of blowback.

    Such a small window for tuning really, but every effective in loading paint faster. Hitting 20bps on an old cocker was a bit of fun.
    Last edited by pbjosh; 11-28-2018 at 03:52 PM.
    Josh Coray
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  2. #52
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    Side curtain calcs to add to our thought process:

    .25" valve would be .125" radius, with a circumference of 0.79 in^2
    .35" valve would be .175" radius, with a circumference of 1.10 in^2

    For the .25" valve:
    At 1/16" travel we get an area of: .049 in^2
    At 1/8" travel we get an area of: .099 in^2

    For the .35" valve:
    At 1/16" travel we get an area of: .069 in^2
    At 1/8" travel we get an area of: .138 in^2

    Now, the older cockers had a .25" hole in the body, giving us .049 in^2

    Not sure on the newer bodies.

    So even the smaller valve potentially hits a saturation point at 1/16" of travel?
    _________________________________________

    I am thinking we might try and do full calculation. Like, we add up energy in the hammer, the poppet valve area, side curtain, poppet spring tension, available chamber volume, volume of valve/ball/barrel and see if anything start making a fun curve.

    Anybody game on this? Like, hammer energy with a couple different springs. Would need to weight some hammers (and the cocking rod) and get rates on the spring. Maybe figure out a way to get velocity (I have 960 fps on my phone)? or calculate what it should be?
    Josh Coray
    J4 Paintball
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  3. #53
    Oh, this is kid in a candy store stuff.

    And may I say for the record that the world would be a better place if all conversations were this information-dense.

    Now, to an earlier question of mine, if what you are saying regarding the curtain area is correct, it seems hardly worth the trouble to worry about opening up the valve body inlet another .030.

    Or is it?

    Thanks again.

  4. #54
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    And may I say for the record that the world would be a better place if all conversations were this information-dense.
    Old timey Warpig or Tinker's guild was more this way. We had some fun stuff in the UberCocker section also.

    Now, to an earlier question of mine, if what you are saying regarding the curtain area is correct, it seems hardly worth the trouble to worry about opening up the valve body inlet another .030.

    Or is it?
    Now, looking at that, I think there is something both for and against more "Post volume, pre-ball capacitance" - PVPBC? Large Capacitance/Small Capacitance? LC/SC?

    In the case of the Poppet we have a weird dynamic where we have a poppet that opens for a period of time that can be mechanically timed, but may have a lot of dynamics, like the flow of air through the system may help close it, or may create back pressure that floats the poppet longer.

    Lets look at the smaller CCM .25" valve vs a RAT or AKA valve. SC vs LC

    In the SC setup, with the smaller valve, there is less pressure holding the valve closed. It has less volume, but less expansion of the air also. Flow might be less than some other setups, but it hits or even matches the saturation point of the body transfer port still. In the setup here also the volume in the bolt is minimal, and it has a smooth expansion area in the bolt.

    So a longer dwell valve would make sense - the system is running at saturation, so a smoother open and close action should still be efficient. Post valve close the

    In a LC setup, larger cup seal, lots of valve room, bigger bolt volume. Say a Rat Valve or the tornado. There is the volume of the RAT valve before the saturation point, and the volume of air behind the body point. maybe twice the volume of a SC valve setup?

    A shorter dwell, as the AKA or Inception valve would produce with their dragging surfaces, or from a heavier spring could flood the area with air, close, and dissipate through the body restriction and bolt as the ball is moving down the system.

    One setup would flow slowly to put constant pressure on the system, and one would charge the area and let the expansion of the air after a closed valve keep acceleration on the ball.

    Now, we get down to the last 50 psi.

    In the SC system, even with a longer dwell, the slower flow results in the chamber not draining everything before it closes. At 300psi you can trap 100psi and still put enough energy on the ball (180in*lbs to 250in*lbs) to fire it.

    In the LC system the valve closes fast, trapping the remaining 50 to 100psi, and using the valve and bolt to retain the energy that the valve has already stopped providing.

    In my setups, using my Bolt (I had a changeable head o-ringless delrin bolt with high tolerance sealing OD) I used BFH* technology. That had a lot of capacity. Some people were able to reduce their operating pressure from 300psi down to 200psi. Why? More retained volume. I also preached higher valve spring sizes at the time, so my bolt worked well with that type of tune.

    The FreeFlow valve and spring were good, but in some setups they wouldn't get enough velocity. But they had a second 'Saturation Point' in the bolt - and decent bolt capacity. So I guessed the system would load up, hold the valve open a bit longer due to back pressure, then it would balance out and close, with enough capacity to dole out air in a smoother manner.

    In your setup? If you are getting a case, don't touch it! That is about max, so leave it be. Also, in the SC System like you have in the one setup, that explain the smoother and quieter action vs the other setup.

    (*Big F-ing Hole)
    Last edited by pbjosh; 11-29-2018 at 10:28 AM.
    Josh Coray
    J4 Paintball
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  5. #55
    Side note: yes, the tinker's guild would have long drawn out threads like this. So miss what that was like.

    Double side note: so that is why the Shiva ran 50psi. It was a pure calculation related gun. Prove the math proves the gun, which proves the theory. I would really love to shoot that gun, or at least hold it, if its still in one piece.

  6. #56
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    Double side note: so that is why the Shiva ran 50psi. It was a pure calculation related gun. Prove the math proves the gun, which proves the theory. I would really love to shoot that gun, or at least hold it, if its still in one piece.
    Yep. It ran 50psi at the LPR, which ran a really small diameter ram. The gun ran at 165psi with a .9ci volume dump chamber. Or just under 150 in*lbs per shot. On a 68/4500 tank with a bit over 300,000 in*lbs per fill, well...Pretty good for a gun designed in the 90's.

    The cycle speed was something stupid like 50 cps on just the bolt. I wish I still had video of that. It was crazy.

    Sadly, a machinist who ran off some parts was making an update and took most of it with him. It was flawed in a couple ways. I will probably rebuild one very close to it in the near future for fun. The drive was basically the same as the Etha/Flex valve, but the bolt was not a blowforward, so it had a far cleaner flow path. Shot so nice.
    Last edited by pbjosh; 11-29-2018 at 03:55 PM.
    Josh Coray
    J4 Paintball
    Lead Design
    www.j4paintball.com

  7. #57
    Eh? What's this?

    Shiva?

    (Pulls up a comfy chair and pours a cup of hot chocolate)

    Go on . . . .

  8. #58
    The Shiva was a design of josh's that he had made when he direct access to Doc Nickels. There should be a pic of it somewhere on the sight. It was very 2000s homebrew with a double trigger frame from an Angel and that is all i remember. Josh will give details, hopefully.

  9. #59
    Agreed on the hopeful details.

    Also, it occurs to me that there may well be good reason to open up the inlet side, simply because it allows for a smaller window of lift, true?

    Just pulled a stock WGP valve from a body and measured the wear marks in the stem, and if they tell the truth, that thing was opening ~.240.

    Think it might be useful, for the purposes of this thread, to pull the valve from the mini, get a measurement for lift height, and then throw that into the mix with a really accurate pressure reading, plus spring rates for valve and hammer.

  10. #60
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    That's really interesting. The springing will be massive in determining lift.

    I have a suspicion based on the old EGO valves that a certain brit actually flow benched these things and found that much over 0.15" is no longer lift limited, but that's not necessarily an argument for restricting the lift to that level.

    I did the valve kinematic analysis for spyders many moons ago (ignoring the fact that they steal air and send it to a 015 ring, blowbacks are actually very dynamically competent under certain refinements).

    I recall that it assorted something like the maximal lift varied mostly as the energy of the spring, but the total energy is dominated by the speed of valve reset, which is pure a=(return mass)/(return force) and t=sqrt(2*lift/a).

    I recall making a thread on I think the Nicad Tinker Guild about superheavy poppets to exploit this difference, and I dabbled with it for 05/06 ego.
    "So you've done this before?"
    "Oh, hell no. But I think it's gonna work."

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