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Thread: Of 'Cocker Valves and Flow Restrictions

  1. #1

    Of 'Cocker Valves and Flow Restrictions

    A question for you engineers:

    Let us say we have two cocker valve bodies, the outlet ports of which do not match up with the inlet port of the gun body. Let us say the gun body inlet port is .250 diameter.

    One valve body outlet port is slightly smaller (say, .230), and one is significantly larger (say, .330).

    The question is, all things otherwise equal, which of these two valve bodies will provide better flow?

    On the one hand, the larger valve outlet port will guarantee that the body inlet has as much air as possible, but this comes at the cost of having a ledge that will surely cause loads of turbulence.

    On the other hand, the smaller outlet port will provide less overall air, but will ensure a smooth transition from valve body to gun body, and will likely have better velocity as well.

    Thanks very kindly!

  2. #2
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    Not to be pedantic but it may depend on what you mean by better flow.

    The steady state mass flow rate for a given pressure is likely to be higher for the larger orifice, just because of the first pass restrictions in series analysis. (For a system with gas velocities this high and viscosities this low, you're basically always turbulent). The old 32 Magnaflow valve did in fact produce an increase in velocity, all other things being equal.

    I concur that the smaller port probably will suffer less energetic losses per unit gas flowed to the ball. This would manifest as better efficiency at the same velocity, albeit at a higher pressure to normalize overall energy flows.

    Also concur that port matching is the best policy. it's a little trickier at the bolt because of machining and such, but the Hardshell Intimidator bolt was my favorite implementation of a stacked tube bolt, since the rear could be 3D machined to a "perfect" flow path..

    Steve and I have kicked around the idea of a resurrection spec control freak valve w/ an angled and matched air path just because I'm so horrified by the Alien morph valve.
    "So you've done this before?"
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  3. #3
    Thanks for the reply!

    I suppose I don't know what I mean by 'better'. Maybe something like CFM or similar.

    But I wonder: if the Magnaflow valve really did increase velocity, isn't it behaving more efficiently?

    In which case, isn't this doing what the smaller port at higher pressure might do?

    Part of this is also loosely tied to another question, namely, whether there really is any meaningful performance difference between high and low pressure.

  4. #4
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    Flowing more air doesn't necessarily mean more efficient, because I could flow more air, but also lose a higher percentage of that air's energy to dissipating factors, and still come out behind after i adjust my velocity to be equal again.

    You also start to get into secondary effects, like the high pressure exerting more closing force on the valve at that point. It's hard to say and might even be gun setup dependent.

    In practice, from a clean sheet design, low pressure tends to always be better, because there's nothing inherent to flow efficiency at high pressures. I tend to observe that most guns feel better at low pressures, though eventually you run into design limitations (like FSDO in spools, possibly farting in sprung poppets) if you run too far below intended.
    "So you've done this before?"
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    Quote Originally Posted by Lurker27 View Post
    Steve and I have kicked around the idea of a resurrection spec control freak valve w/ an angled and matched air path just because I'm so horrified by the Alien morph valve.
    I would love to see that happen.
    OlllllllO

  6. #6
    Quote Originally Posted by Lurker27 View Post
    Flowing more air doesn't necessarily mean more efficient, because I could flow more air, but also lose a higher percentage of that air's energy to dissipating factors, and still come out behind after i adjust my velocity to be equal again.

    You also start to get into secondary effects, like the high pressure exerting more closing force on the valve at that point. It's hard to say and might even be gun setup dependent.

    In practice, from a clean sheet design, low pressure tends to always be better, because there's nothing inherent to flow efficiency at high pressures. I tend to observe that most guns feel better at low pressures, though eventually you run into design limitations (like FSDO in spools, possibly farting in sprung poppets) if you run too far below intended.

    Thanks again.

    To add a case in point to this discussion, how is a valve like the Tornado, with its absurdly huge, mismatched exhaust port, able to get such great efficiency numbers relative to other, better-matched valves like the CCM and WGP?

    It cannot be simply the rapid closing feature, as it seems nearly identical to the RAT valve in that respect, and those aren't considered to be at the same level of performance (even though in my limited perspective they should perform equally well, as they seem to have most of the essential features of the Tornado).

    Just trying to get my head around how this stuff works.

  7. #7
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    It's my opinion that the valve guide arms on the tornado and Resurrection valve head lead to significantly decreased closing time (and definitely no valve float).

    I had to Google a rat valve but this feature seems absent.

  8. #8
    Gotcha.

    And just so that we are on the same page, how are you meaning 'valve float'?

    I know what that means in the automotive arena, but not necessarily here.

    You mean just too much lift, for too much duration?

    Am actually curious about those guide arms/fins. They don't restrict flow overmuch? And do they also help stabilize the valve stem/cup seal in use?

    Have seen some mighty worn valves with cup seals that just flopped around in the body and wondered how to prevent that sort of damage in use.

  9. #9
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    I doubt the arms restrict significantly compared to the main throat/annulus restriction.

    I actually mean by float essentially the same thing as in automotive - the valve pin losing contact with the actuator. (hammer) I have no idea if this ever happens practically in an autococker, but there are reasons to think it could happen in some poppet implementations.
    "So you've done this before?"
    "Oh, hell no. But I think it's gonna work."

  10. #10
    Again, thank you.

    Can you say a bit more about how those fins help with closing time?

    Do they create a kind of force differential in that they don't contribute to opening force when the poppet is sealed up, but add to closing force when the poppet is open?

    Just a guess, so do pardon if that's silly.

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