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Thread: Foster Style Check Valve?

  1. #1
    Moderator rsterne's Avatar
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    Foster Style Check Valve?

    Any reason I can't use a shortened Foster style check valve in a pumper? It will ride in a 5/32" (or maybe 0.160") hole in the front of the valve, and only has about the same area around it for headspace as a 0.040" - 0.060" hole of the same length (I was thinking about 1/4" - 5/16" long for the stem).... They don't use springs in a Foster to help it seal and I'm thinking of trying it that way, just a small pin in the valve to prevent it from falling/blowing inside on the fill stroke....

    Anybody done this, or forsee a problem doing it?....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  2. #2
    Administrator AirGunEric's Avatar
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    Other than the moving pin issue you mention, I don't see a problem if you can get everything to fit together. However, the question is "why"? You want to attach a bottle directly to the valve to avoid pumping?
    I'd say I care- but I'd probably be lying...


  3. #3
    Moderator rsterne's Avatar
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    I don't intend to use the Foster fitting, just the check valve from one.... It would be inserted into a hole in the end of the valve, sitting against a shoulder from the inside.... My reasoning is that it should be easier to get to seal than a Delrin check, and take up less volume inside the valve.... I should add that I'm scratch building a new front end for a Disco valve for this project.... It will incorporate a gauge mount and have an internal volume of about 5cc (3 times the volume of a 13XX valve)....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  4. #4
    Administrator AirGunEric's Avatar
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    Shoot- should have read your mounting specifications, didn't think about it- just figured it was going in a QD fitting...
    I'd say I care- but I'd probably be lying...


  5. #5
    Member Gippeto's Avatar
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    Will be less efficient than a check with a spring...there's always going to be some bleed back before it seats and seals.

    You may also wish to check out floating o-ring/check valve for the pump head...might allow a slight increase in swept volume over the Crosman design.

    http://www.network54.com/Forum/27568...ng+check+valve

    Al

  6. #6
    Moderator rsterne's Avatar
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    HI Al....

    Those articles are what sent me down this path.... Is the reason you say there will be some bleed back is that the stem of the check must move first?.... If so, then why not fasten it in place with, for example, a set screw.... so that only the O-ring is moving?.... I realize that the dialating O-ring check valve design has only the O-ring moving.... it is expanding on the compression stroke and then contracting and being forced against the stem and the end of the valve on the intake stroke.... Why do you feel that the Foster style check will bleed back before sealing?.... Would you still feel the same way if there was a very light spring holding it seated?....

    I noticed your floating O-ring design for the pump head.... I can understand how that bypasses on the intake stroke.... but wouldn't it require a rather slow return stroke or you would be pulling against a fair resistance.... Or, is it in fact better than a conventional flat-topped design which pulls against a vacuum for part of the stroke?.... Why do you think you could get increased stroke length over a flat-topped piston with O-ring?.... The length of slot is basically governed by the pump linkage clearing the tube, is it not?....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  7. #7
    Senior Member SeanMP's Avatar
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    Quote Originally Posted by rsterne View Post
    HI Al....
    .... Why do you think you could get increased stroke length over a flat-topped piston with O-ring?.... The length of slot is basically governed by the pump linkage clearing the tube, is it not?....
    Bob
    Just jumped in to make sure I understand correctly...
    Your floating Oring variable design allows you to take half a stroke or a quarter stroke ...for when the pumping has gotten real tough and your trying to squeeze in the last little bit?

    Bob
    I think your springless poppet should work fine. especially if the poppet stem was finely fitted. I would think leaded brass for the poppet for it's finely machined finish.
    Sean

  8. #8
    Moderator rsterne's Avatar
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    Sean....

    I was just planning on using a chromed Foster check valve poppet, I have a spare.... just shorten it by about half.... Good point about the finish, though, I should try and get the hole ASAP (as smooth as possible).... I wonder how much the O-ring will crush under pressure (ie how far I have to leave the stem short of the end of the valve so the piston doesn't hit it).... Gotta have minimum headspace, ya'know....

    Al, any changes you would make to your piston design to reduce the headspace losses?....

    Bob
    Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
    Airsonal: Too many to count!

  9. #9
    Member Gippeto's Avatar
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    Have found that foster checks will bleed back when the orientation allows and flow rate is low...as it would be when pumping a pumper...They always seem to be pointing at the sky when I pump 'em anyway....spring loaded would take care of this.

    The usual FTP setup has to come out past the slot and then return into the slot before compression begins..as I recall, the slot is actually a little longer than really needed for the linkages...it is possible I'm mistaken, but I don't think so. If you're intention is to use a "factory" tube, then the slot isn't going to change and no benefit there...would definitely allow the half strokes Sean mentions. There is little resistance when "reloading" the pump cylinder with air...in any event, the effort required to "reload" the pump cylinder should be lower than if it were attempting to pull a vacuum.

    Al

    Edit: Changes to the picture I posted? Certainly. Out of time atm...will get back to this tonight.

  10. #10
    Senior Member SeanMP's Avatar
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    Bob

    Just for fun I just put a 007 under a spring tester. It seems to squish to 50% easily(150lb/f) then the force required to to squish it more jumps exponentially
    Sean

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