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Thread: Threading and Oring gland help

  1. #21
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    I haven't run into that scenario YET. It would be interesting to know as well.

    What I have now is a dump valve seal that can't be designed with a floating-type seal. It needs to be stretched into it's gland so it won't blow out. The gland itself has been designed, but I'm sizing the ID of the bolt and don't know how much squeeze I should run. Since I'm not using extrusion to make the seal, I need to put squeeze on there which is horrible for friction and FSDO in this particular case.

  2. #22
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    OK, so I would call that stretch, rather than squeeze, but I see what you mean. You want to put some squeeze on the seal by the bolt sliding over it.
    Is it atmosphere on one side and chamber pressure on the other? If so, then very little squeeze is needed. I have to admit that I would always deal with this kind of problem with a suck it and see approach. I would spec the internal diameter of the bolt first, because this is the critical dimension for your force calculations. Then I would take the seal closest to the bolt ID that is smaller than the ID. I would then guestimate the groove dimension for the gland, based on previous experience, and then add a little bit. I'd have the parts made, test it, and if I wasn't happy with the frictional result (testing by feel and by hand) I would offer up the part in the lathe and skim 0.05-0.10mm at a time out of te groove until I was happy with the fit. Then I'd measure it, amend the drawing, and have a second sample made at the factory.

    I know that may not be much help, but I hope it shows that there isn't really a cast-iron method of doing this and it is still, for me, a case of trial and error.

    That process is for dynamic seals, of course. Static is far easier and more forgiving.

    Regarding the other scenario I asked about, I have never had ANY success in doing that. Putting a larger o-ring into a smaller internal groove to squeeze it down to a shaft has never worked for me.

    Jack

  3. #23
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    Quote Originally Posted by PBSteve View Post
    I may or may not be telling you something you already know, but Figure 3-3 in the bible is actually pretty good for making estimates on loss of diameter due to stretch. I follow the "observed" curve.
    Bible - anyone have a link to this?

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  5. #25
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    That parker oring handbook is hosted on dozens of sites. It has some good basics to wade through, but I never realized how specialized paintball glands really were. BL runs right on that fine line of minimal friction and poor seal. Others run a little more friction but are a lot more reliable. Then, lube plays a big part in friction reduction.

  6. #26
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    So, this has been working somewhat decently for me to use the floating gland technique. I have found that I do like the depth to be about .073" or so and the width to be .078" or wider. The one I haven't quite figured out is the clearances... It seems like more separation between the parts (larger extrusion gap) actually improves the seal. It seems like a diametric clearance of ~.006-.008 works best. Is that pretty close to what others are seeing?

    As a side note, this seems to make a significant difference in the shot characteristics.

  7. #27
    Sounds a lot like my dimensions that I mentioned earlier Clearance is the same range also.

  8. #28
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    Do you have a good starting point like that for non-ambient seals? Meaning cases such as the axe valve where both sides are pressurized... the floating type gland doesn't work very well there. My guess like a .068" or so offset (depth) with a width of like .073" would be good, but I haven't been successful there yet.

    It is the glands you recommended. Thanks for the advice. The only thing I've really learned from experimenting beyond what you've said is that I haven't had as good of luck going with a gland deeper than about .073".

  9. #29
    Not done too much with those seals to have a set of rules for it. They tend to suck is my simple answer, and I try to avoid them. We had some issues tuning in the o-ring on the axe poppet to make it work in all conditions. I often tell the story of taking the test guns to EMR to play, both being phenomenal in the lab, and then neither working at the event. The change in temp and altitude made that o-ring leak. I believe I increased the diameter by 0.005" and re tested it and everything has been good since. It's why I implemented a World Wide field test policy (that certain people at KEE then dismantled in the last couple of years before I left, and to my utter frustration).

  10. #30
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    Lol, they certainly do suck in my limited experience. I suppose the ones on the ID of the vanquish for the air shutoff would be similar as well. To be clear, you were right around .070" on depth (assuming you started at .075" and increased .005")?

    For one of the projects I'm messing with, NT spool and can, I just reverse engineered all of the existing gland dimensions for the application and stuck with it. I didn't feel like reinventing the wheel there.


    BTW, thanks again for your help on this. It's already costing money to learn these lessons 1st hand, but you're saving me a ton!

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