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Thread: No substitutes: Polyurethane just can't be replaced.

  1. #1

    No substitutes: Polyurethane just can't be replaced.

    Tags: Can I use butyl nitrate o rings o-rings orings instead of polyurethane automag AGD

    Anyways, I had a terrible leak down the barrel, turned off when the trigger was pulled, changed the power tube spacer (o rings .010) multiple times (.220 .225 .230), and nothign worked. I was using butyl.

    I switched it out with some 5 year old polyurethane orings i had laying around. BAM leak gone.

    I also noticed that polyurethane was important for the regulator valve pin assembly (.006). I got it to work with butyl - eventually, but I feel poly would have solved all the problems.

    So, I think the point of this thread is people should mention what parts of the valve simply can't be replaced with butyl - which is becoming more prevelant and polyurethane being more rare.

    Also, people should mention what sorts of local stores carry polyurethane!

  2. #2
    I've got nowhere close to me that I know of that carries urethane o-rings. I have to order them from McMaster or get them from AGD kits.

    Buna-N o-rings are all over the place though.

  3. #3
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    I order all my o-rings from my local hydraulics shop, I just walk in and ask for the sizes I need whether buna-n or polyurethane and it's usually in stock.
    A proud Canadian EH

  4. #4
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    Quote Originally Posted by halB View Post
    polyurethane being more rare.

    Also, people should mention what sorts of local stores carry polyurethane!
    They may not be very attainable at the local level, but AGD and Tuna both carry these in stock at all times. The problem is that people don't want to pay the price. It irks me to no end when someone spends $500 on an Emag and *****es about having to spend $30 on an O-ring kit. Seriously.

  5. #5
    Quote Originally Posted by OPBN View Post
    They may not be very attainable at the local level, but AGD and Tuna both carry these in stock at all times. The problem is that people don't want to pay the price. It irks me to no end when someone spends $500 on an Emag and *****es about having to spend $30 on an O-ring kit. Seriously.
    Agreed.

    The 12 threads opened this week could have been mostly solved with one new factory rebuild kit.

  6. #6
    Quote Originally Posted by OPBN View Post
    The problem is that people don't want to pay the price. It irks me to no end when someone spends $500 on an Emag and *****es about having to spend $30 on an O-ring kit. Seriously.
    Well you've got to admit, an Emag at $500 is a steal. An o-ring kit that contains about $7 worth of o-rings at $30 isn't as good of a deal, especially if you can get the one o-ring you need locally for $1 or less. Paintballers who buy pretty much everything except paint on the used market tend to always look for ways of making things as cheap as possible.

    Now I'm not knocking Tuna or the AGD store at all. I've placed orders with both on multiple occasions. But there's a reason people post WTB threads in the BST looking for things such as sears and pins, field strip screws, etc., just like there's a reason people sell those items in the BST too.

  7. #7
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    I live in BFE, so the chances of me getting poly o-rings is nil. My point is more along the lines of people not wanting to spend the money to do it right. If you have invested $500+ in a nice marker, don't be such a tightwad about spending the money you need to buy the right parts to fix it correctly. People need to realize that certain Orings are used for a reason, not just for giggles. Same with using the right oil instead of spraying it down with WD 40.

  8. #8
    Quote Originally Posted by OPBN View Post
    People need to realize that certain Orings are used for a reason, not just for giggles. Same with using the right oil instead of spraying it down with WD 40.
    Now that I'll agree with. Quality in means quality out, and that goes for everything that enters the valve and marker. Pretty much, TK & Co. did the research and gave us a detailed list as to what needs to be your inputs when it comes to the valve, in order to maintain the AGD standard of quality. That means urethane o-rings on everything except the Emag quad on/off o-ring.

  9. #9
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    so what are all the sizes of the orings needed in a valve including the quad?
    My sydarm weighs less than yours!!!

  10. #10
    Nobody has really defined what "do it right" really technically means, which I think is OP's original question. And it's not just AGD's nonexistent word for it, because they kind of overengineered all kinds of stuff.

    You want the urethane for the moving seals. The power tube o-ring is probably one of the more important ones to have in urethane, more so for LX bolt.

    For something that's static, like the outer on-off o-ring, I don't see why that one can't be buna. It's the inner one that gets the movement, and that's why that one is teflon. However, seeing as all that o-ring is doing is keeping the thing off until you release the sear, I don't really consider it that critical. It can leak a little bit, and all that means is your chamber gets a little more air, or your LX might start venting. Hell my current mag has a tiny leak down the barrel when I hold the trigger down. It's not like I run around with the trigger held down, so I haven't even bothered to change it out, and it hasn't affected me.

    The last time I saw a problem with that outer on-off oring, it was simply because the o-ring itself was badly manufactured -- there was a visible defect on it. Maybe the previous owner had recycled a Q/D o-ring and threw it in there in a pinch. So if you did see a problem with non-urethane, don't automatically assume it's just because of the material.

    What I have yet to see data on is how long the various materials actually wind up lasting in a gun. I think that's where you'll be able to really calculate the tradeoffs.

    Other nagging issuse to consider:

    If an o-ring maybe only lasts half as long in buna vs urethane in an application, but costs only 1/4 what the urethane one, do you come out ahead? What if the original lasts 5 years, and the buna lasts only 2.5, but you bought 4 for the same price? Some of the price differentials are pretty significant.

    I've also had a problem with urethane o-rings degrading by themselves over time. Look up "polyurethane o-ring shelf life". So you might stock up on polyurethane o-rings, and then 10 years down the line when you need to fish its replacement out, you find that the thing is all cracked and brittle already. Meanwhile a buna one was cheaper already and might have a shelf life of 15 years.

    I think this is interesting data to have at least on an intellectual level, regardless of how much money you fed into your gun already.
    "Accuracy by aiming."


    Definitely not on the A-Team.

  11. #11
    Quote Originally Posted by GoatBoy View Post
    ... they kind of overengineered all kinds of stuff.
    Does not compute. April fool's?

  12. #12
    Quote Originally Posted by Justus View Post
    Does not compute. April fool's?
    Nah, srsly.

    http://www.reactionface.info/sites/d...0497097772.gif

    There are some things that are clearly designed to last pretty much forever, which I can understand.

    But forever divided by 2 is still not bad.
    Last edited by AO Moderation Team; 04-03-2013 at 09:30 PM.

  13. #13
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    Quote Originally Posted by GoatBoy View Post
    You want the urethane for the moving seals. The power tube o-ring is probably one of the more important ones to have in urethane, more so for LX bolt.
    This holds for most things. The LX actually works really well with buna but it does wear out quickly. The softer buna reduces bolt stick issues due to having a carrier that is a tiny bit too tight.

    Quote Originally Posted by GoatBoy View Post
    For something that's static, like the outer on-off o-ring, I don't see why that one can't be buna. It's the inner one that gets the movement, and that's why that one is teflon.
    The teflon is in place because it doesn't harden when it freezes when CO2 passes by it unlike urethane or buna.

    Quote Originally Posted by GoatBoy View Post
    However, seeing as all that o-ring is doing is keeping the thing off until you release the sear, I don't really consider it that critical. It can leak a little bit, and all that means is your chamber gets a little more air, or your LX might start venting. Hell my current mag has a tiny leak down the barrel when I hold the trigger down. It's not like I run around with the trigger held down, so I haven't even bothered to change it out, and it hasn't affected me.
    It is quite critical. If this oring leaks it causes bolt stick issues. The tiny leak you hear when you hold the trigger is caused by residual pressure in the chamber leaking out past the carrier oring because the vent hole is really close to the bolt stem vent hole and you are using a perfectly fitting carrier. If you have shims installed, removing them will probably make the leak go away. It goes away when the trigger is released because the additional chamber pressure on the oring tightens it up.

    Quote Originally Posted by GoatBoy View Post
    The last time I saw a problem with that outer on-off oring, it was simply because the o-ring itself was badly manufactured -- there was a visible defect on it. Maybe the previous owner had recycled a Q/D o-ring and threw it in there in a pinch. So if you did see a problem with non-urethane, don't automatically assume it's just because of the material.

    What I have yet to see data on is how long the various materials actually wind up lasting in a gun. I think that's where you'll be able to really calculate the tradeoffs.
    Its not always about life of the oring. Urethane is stiffer than buna. If you look at the elasticity of the two types, buna has much greater elasticity than urethane. Urethane also has a larger pressure rating. If there are large gaps to allow air flow when a passage is opened, buna can get pushed out of place easily but urethane will stay in place. In these situations, buna will get pinched and leak.
    Except for the Automag in front, its usually the man behind the equipment that counts.

  14. #14
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    I can't tell you how many guns come through my hands that need nothing more than a simple rebuild and new main spring. I have even seen people throw fits claiming that new parts were no good, yet the gun had a busted mainspring...

    "I'm not happy unless you're not happy"

  15. #15
    Does anyone here know if the rebuild kits come with O-Rings that fit a Classic RT Banjo Bolt?

  16. #16
    Quote Originally Posted by pgop2.0 View Post
    Does anyone here know if the rebuild kits come with O-Rings that fit a Classic RT Banjo Bolt?
    I've only seen the RT banjo bolt o-rings reported as size 009. I'm pretty sure that won't come in the X-valve rebuild kit.

    Edit: Should be in here though - http://www.tunamart.com/index.php?c=42&p=79

  17. #17
    Quote Originally Posted by athomas View Post
    The teflon is in place because it doesn't harden when it freezes when CO2 passes by it unlike urethane or buna.
    I get what you're saying. I don't run CO2 in my mag currently, and nobody's running CO2 in any of the RT's (needs to be asked though if CO2 is the answer, why are they used in RT's?). Ironically, I pull those 006 o-rings from my AGD parts kits and use them in my Tiberius Magazines for that exact reason. The top o-ring in Tiberius mags tend to suffer this exact damage from CO2.

    Quote Originally Posted by athomas View Post
    It is quite critical. If this oring leaks it causes bolt stick issues. The tiny leak you hear when you hold the trigger is caused by residual pressure in the chamber leaking out past the carrier oring because the vent hole is really close to the bolt stem vent hole and you are using a perfectly fitting carrier. If you have shims installed, removing them will probably make the leak go away. It goes away when the trigger is released because the additional chamber pressure on the oring tightens it up.
    I have my LX bolt adjusted with max shims, as instructed, and my carrier is nice and broken in now. I don't have bolt stick. That's what the shimming prevents, so there's nothing wrong with my LX config. As long as the gun doesn't go into runaway, I'm not really motivated to get into the gun. Maybe if I had an L7 bolt this would be an issue. As it stands, it's not critical. The gun's had a slight on/off leak for probably more than a year without issues.

    Quote Originally Posted by athomas View Post
    Its not always about life of the oring. Urethane is stiffer than buna. If you look at the elasticity of the two types, buna has much greater elasticity than urethane. Urethane also has a larger pressure rating. If there are large gaps to allow air flow when a passage is opened, buna can get pushed out of place easily but urethane will stay in place. In these situations, buna will get pinched and leak.
    But look at the case of some of the o-rings. They're not going anywhere. It's not like that Pro-Team cocker disaster where that front o-ring gets to leave home.

    The on/off o-rings are pretty much captive. Where are they going to go?

    Where's that giant o-ring on the back of the regulator going to go? Is CO2 passing through it? Is that a static or dynamic seal?

    Where's the o-ring on the power tube tip going to go? Is that a static or dynamic seal?

    Hell, is it really necessary to have urethane o-rings on the twist-lock barrels? What PSI rating do twist-lock barrel o-rings need to have?

    So again I question the assertion of "doing it right", as the actual parameters for "right" are unspecified. OK, a buna o-ring will wiggle a little more. How much is too much?

    I'll have to dig into some of my much older variant parts kits because I swear I saw non-teflon 006's and non-urethane 010's (?).

    I probably don't make a good test subject though as I shoot less than a bag a day.

  18. #18
    Quote Originally Posted by GoatBoy View Post
    Hell, is it really necessary to have urethane o-rings on the twist-lock barrels? What PSI rating do twist-lock barrel o-rings need to have?
    Yes. And it's not about the psi, it's about whether you intend on removing the barrel frequently or not. If so, use urethane o-rings to save yourself the headache. Especially if you're shooting a Minimag or Classic RT.

    Quote Originally Posted by GoatBoy View Post
    So again I question the assertion of "doing it right", as the actual parameters for "right" are unspecified. OK, a buna o-ring will wiggle a little more. How much is too much?
    Let's just put it this way, there's spec, and then there's not spec. Can you use out-of-spec parts and make it work? Maybe. But if you want it to definitely work every time, use the parts/materials that the manufacturer supplies and recommends.

    Quote Originally Posted by GoatBoy View Post
    I'll have to dig into some of my much older variant parts kits because I swear I saw non-teflon 006's and non-urethane 010's (?).
    I don't know where you may have gotten the non-urethane 010 o-rings, but they wouldn't have come from an OEM parts kit. The non-teflon 006 o-rings are fine. You only use teflon o-rings in the Classic on/off, not in the RT, RTP, Emag, X, etc.

  19. #19
    Oh, oops. Had to doublecheck that -- yes, the RT's use urethane for that 006. Makes sense.

    The spec issue is... hard to argue.

  20. #20
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    Quote Originally Posted by GoatBoy View Post
    I have my LX bolt adjusted with max shims, as instructed, and my carrier is nice and broken in now. I don't have bolt stick. That's what the shimming prevents, so there's nothing wrong with my LX config. As long as the gun doesn't go into runaway, I'm not really motivated to get into the gun. Maybe if I had an L7 bolt this would be an issue. As it stands, it's not critical. The gun's had a slight on/off leak for probably more than a year without issues.
    The level 10 should not have any shims if it is working properly. The shims do nothing to prevent bolt stick. You only need shims if the bolt can't travel far enough to vent air to reset. The shims shorten the distance that the bolt needs to travel. If the bolt fires or vents at all, then shims don't help. In your case, they are introducing a slight leak when you hold the trigger. Yours isn't an on-off leak, unless it is leaking into the grip frame(in that case it would be a lower on-off leak).


    Quote Originally Posted by GoatBoy View Post
    But look at the case of some of the o-rings. They're not going anywhere. It's not like that Pro-Team cocker disaster where that front o-ring gets to leave home.

    The on/off o-rings are pretty much captive. Where are they going to go?
    In the case of the on-off orings, I would be more worried because they are two orings nested inside one another rather than an oring trapped by metal. In the case of the oring tightly fitted by metal or hard boundaries, then I think you are on track and the buna would be fine. The emag quad oring is actually buna. The outer oring is urethane though, because it is required to be rigid to hold the inner oring in place. Without the outer oring being rigid it could get pushed out causing the inner oring to get off center.

    Quote Originally Posted by GoatBoy View Post
    Where's that giant o-ring on the back of the regulator going to go? Is CO2 passing through it? Is that a static or dynamic seal?
    It is a dynamic oring. The regulator piston moves back and forth each time the chamber empties. A proper fitting buna oring might work quite well here too, unless you get up to the rated pressure of the mag valve. At that pressure, the buna oring would distort and get pushed out the sides and jam the piston. Theoretically, this couldn't happen, because the over pressure release should open before that happens.

    Quote Originally Posted by GoatBoy View Post
    Where's the o-ring on the power tube tip going to go? Is that a static or dynamic seal?
    The power tube tip could definitely use a buna oring. It is just a friction oring. The urethane one is used because it is already a stock item for an oring size that is used in other parts of the marker. No need to have another stock number to include in the parts list.

    Quote Originally Posted by GoatBoy View Post
    Hell, is it really necessary to have urethane o-rings on the twist-lock barrels? What PSI rating do twist-lock barrel o-rings need to have?
    This one is actually necessary. The buna orings are too soft and would cause massive barrel wobble when firing the gun.

    Quote Originally Posted by GoatBoy View Post
    So again I question the assertion of "doing it right", as the actual parameters for "right" are unspecified. OK, a buna o-ring will wiggle a little more. How much is too much?
    Too much is when they get jammed down between a wall and a piston or if it rolls due to pressure and it causes a leak. Its easier to spec all urethane and be sure that it works all the time than to spec urethane for some and buna for others and have the odd failure due to buna stretching because it wasn't as forgiving to the installer. From a quality control point of view, it is less of a headache for the customer service department. Heck, I've even seen poor quality aftermarket urethane orings that didn't perform well, so don't think that its only buna that we are saying to stay away from. Good quality urethane orings have a better rate of success, plus it is easier for average users to source lower quality buna and really have problems than it is for them to source lower quality urethane orings. Generally, the urethane orings are better quality anyway.

    Quote Originally Posted by GoatBoy View Post
    I'll have to dig into some of my much older variant parts kits because I swear I saw non-teflon 006's and non-urethane 010's (?).
    These wouldn't have been AGD kits.

    It never hurts to question why things are done the way they are done. It brings out good discussion. Sometimes we discover things that don't need to be the way they are, or that things have changed since the original design such that the parameters no longer dictate the use of a specific part as originally designed.

  21. #21

    It's got what plants crave!

    Quote Originally Posted by athomas View Post
    The level 10 should not have any shims if it is working properly. The shims do nothing to prevent bolt stick. You only need shims if the bolt can't travel far enough to vent air to reset. The shims shorten the distance that the bolt needs to travel. If the bolt fires or vents at all, then shims don't help. In your case, they are introducing a slight leak when you hold the trigger. Yours isn't an on-off leak, unless it is leaking into the grip frame(in that case it would be a lower on-off leak).
    Are we mixing up terms?

    If my on/off *isn't* leaking, then with the trigger held down, I might get a short amount of air out the front as residual pressure leaves the chamber, and then it's over. There is no more air to leak out because the on/off has *shut off the supply of air to the dump chamber*.

    However, if the on/off *is* leaking, then the dump chamber continues to build up pressure even with the trigger held down, and eventually gets enough pressure to get the bolt to overcome spring force, move forward a tiny bit and start venting. If it's not a huge leak, then it only builds enough pressure to vent instead of going into full auto, which is what I'm saying.


    Quote Originally Posted by athomas View Post
    It is a dynamic oring. The regulator piston moves back and forth each time the chamber empties. A proper fitting buna oring might work quite well here too, unless you get up to the rated pressure of the mag valve. At that pressure, the buna oring would distort and get pushed out the sides and jam the piston. Theoretically, this couldn't happen, because the over pressure release should open before that happens.
    I'm not talking about that o-ring (although I'm tempted to try a buna in there as well) -- I'm talking about the big fat one that is between the regulator halves.

    And the whole bit about 3000PSI input to the valve is definitely along the lines of overengineering.


    Quote Originally Posted by athomas View Post
    This one is actually necessary. The buna orings are too soft and would cause massive barrel wobble when firing the gun.
    So at this point I have to ask: what's the difference between a 90 durometer urethane o-ring and a 90 durometer buna o-ring, particularly for TL barrel use?


    Quote Originally Posted by athomas View Post
    From a quality control point of view, it is less of a headache for the customer service department. Heck, I've even seen poor quality aftermarket urethane orings that didn't perform well, so don't think that its only buna that we are saying to stay away from. Good quality urethane orings have a better rate of success, plus it is easier for average users to source lower quality buna and really have problems than it is for them to source lower quality urethane orings. Generally, the urethane orings are better quality anyway.
    This is the most believable and practical reason, and I believe it.

    But it has nothing to do with a technical spec, and more to do with non-technical issues. Terminology matters -- instead of "lower quality buna", you could say, "out of spec buna". But that gets us right back to the question about "what are the specs"?

    And the spec from AGD for, say, the power tube or on/off o-ring isn't "90 durometer urethane 010 o-ring".

    The spec is, "AGD Part #00123". Which is a pretty crappy spec. Nowhere on AGD's site do I see them give specifications for any o-rings. (And yes, I realize this is no different from pretty much any other manufacturer.)

    That's what leads people to blindly go, "You should use AGD o-rings because they're up to spec". And then faced with the question, "Wait, what's the spec?", the response is, "The AGD o-rings." Which should remind you all of a certain movie...



    Without an actual specification (while all the stuff you say is interesting, it is all as equally hypothetical as anything that I say) or *people actually trying it out*, then we don't really know.

    I wouldn't mind trying some of it out just to see.

  22. #22
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    Quote Originally Posted by GoatBoy View Post
    Are we mixing up terms?

    If my on/off *isn't* leaking, then with the trigger held down, I might get a short amount of air out the front as residual pressure leaves the chamber, and then it's over. There is no more air to leak out because the on/off has *shut off the supply of air to the dump chamber*.

    However, if the on/off *is* leaking, then the dump chamber continues to build up pressure even with the trigger held down, and eventually gets enough pressure to get the bolt to overcome spring force, move forward a tiny bit and start venting. If it's not a huge leak, then it only builds enough pressure to vent instead of going into full auto, which is what I'm saying.
    With a level 10 bolt, the volume of air left in the chamber is quite large. It will weep out for quite a while when the trigger is held in. A tiny on-off leak can also cause the problem as you indicated. However, past history has proven that any time there are shims installed and you get weeping out the front, then the shims are to blame. Usually, an on-off leak will result in bolt stick issues along with the leak.




    Quote Originally Posted by GoatBoy View Post
    I'm not talking about that o-ring (although I'm tempted to try a buna in there as well) -- I'm talking about the big fat one that is between the regulator halves.

    And the whole bit about 3000PSI input to the valve is definitely along the lines of overengineering.
    Ok. I agree with you, it doesn't need to be urethane other than to meet the 3000psi spec.




    Quote Originally Posted by GoatBoy View Post
    So at this point I have to ask: what's the difference between a 90 durometer urethane o-ring and a 90 durometer buna o-ring, particularly for TL barrel use?
    The durometer rating is the hardness rating for small area stress. The elastic modulus rating is for the oring overall. Even though they have the same durometer rating, they will respond differently to the same pressures as a whole. In the case of the barrel orings, the buna orings will stretch and roll around more.




    Quote Originally Posted by GoatBoy View Post
    This is the most believable and practical reason, and I believe it.

    But it has nothing to do with a technical spec, and more to do with non-technical issues. Terminology matters -- instead of "lower quality buna", you could say, "out of spec buna". But that gets us right back to the question about "what are the specs"?

    And the spec from AGD for, say, the power tube or on/off o-ring isn't "90 durometer urethane 010 o-ring".

    The spec is, "AGD Part #00123". Which is a pretty crappy spec. Nowhere on AGD's site do I see them give specifications for any o-rings. (And yes, I realize this is no different from pretty much any other manufacturer.)

    That's what leads people to blindly go, "You should use AGD o-rings because they're up to spec". And then faced with the question, "Wait, what's the spec?", the response is, "The AGD o-rings."



    Without an actual specification (while all the stuff you say is interesting, it is all as equally hypothetical as anything that I say) or *people actually trying it out*, then we don't really know.

    I wouldn't mind trying some of it out just to see.
    I do agree that the term specs is thrown around loosely. Its like any other manufacturer not wanting to give away their specs. We just know that the products they provide work so we use them. I don't mind getting my own orings. I just make sure I buy good quality. Those that understand pressures and tolerances can probably change out some of the orings for different types and not have any issues. The majority cannot. It is generically stated because anything more than that for the average user can get confusing.

  23. #23
    When it comes to specs, the AGD community has also done a little "reverse engineering" (for lack of better term) on o-rings, too. We know that AGD Part #779 is a -006 urethane 90D o-ring. We know that AGD Part #123 is a -010 urethane 90D o-ring. Etc.

    That's why when we say "use the specified part", we don't necessarily mean you have to buy the o-ring from the manufacturer, just use the same thing the manufacturer does. A urethane 90D o-ring of the right size does not have anything magical about it just because it came in a parts kit. It's the same as any other urethane 90D o-ring (throwing out manufacturer defects). But it's quite different from a buna-N o-ring of the same size.

  24. #24
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    Quote Originally Posted by Justus View Post
    That's why when we say "use the specified part", we don't necessarily mean you have to buy the o-ring from the manufacturer, just use the same thing the manufacturer does. A urethane 90D o-ring of the right size does not have anything magical about it just because it came in a parts kit. It's the same as any other urethane 90D o-ring (throwing out manufacturer defects). But it's quite different from a buna-N o-ring of the same size.
    I agree on this. I was using the example at hand. The OP was having massive issues with an Emag valve that the o-rings were goo in . Several times in another thread, he was told to use Urethane o-rings, but insisted on continuing using something else. I don't care where anyone gets their o-rings, as long as they are the right size/material that is specified. Personally, I found it to be easiest (not cheapest) to just pick up an O-ring kit and replace what I use as needed. Does it cost me more, yeah but I know they're correct. I also agree that not all Urethane O-rings are created equally. I have a 32* kit that every o-ring out of it has essentially failed within minutes of use. Probably because it's old, but regardless none of the ones I have gotten from AGD or Tuna has ever failed out of the box.

  25. #25
    To be clear: I'm not saying that urethane and buna are the same. They will have different properties. That's why I keep digging at the properties and contexts of usage.


    Quote Originally Posted by athomas View Post
    The durometer rating is the hardness rating for small area stress. The elastic modulus rating is for the oring overall. Even though they have the same durometer rating, they will respond differently to the same pressures as a whole. In the case of the barrel orings, the buna orings will stretch and roll around more.
    Well, here we have a matter of scale, which definitely matters. But if the difference between one and the other is scale -- "large" area vs. "small" area, how "small" is small? In many of these o-rings, it's arguable that the affected areas are relatively small. It's not like we're talking about solid rocket boosters or something. Instead of "small area", is there some sort of equivalent for something like Reynold's number to determine what "scale" you're at?

    By the way, I looked in my parts box -- the two black o-rings I saw were... TL barrel (may or may not be from AGD; I had so many parts kits that unfortunately I opened them and consolidated them), and the lower ULT o-ring, which I do know was from AGD.


    Quote Originally Posted by athomas View Post
    I just make sure I buy good quality. Those that understand pressures and tolerances can probably change out some of the orings for different types and not have any issues. The majority cannot. It is generically stated because anything more than that for the average user can get confusing.
    And there again I caution against the use of the word 'quality'. How do you know they're good 'quality'? Because they meet specs. Specs which are defined, quantifiable, and measurable. This is different from the warm fuzzy feeling you get from buying o-rings from someone reputable. Most people use 'quality' to refer to the latter.



    So let's play a game. As I like to say, the best indicator of understanding is predictive ability.

    In a totally-hypothetical-and-not-at-all-real-and-did-not-happen-last-night-at-all make-believe scenario, I hop online and buy 5 each of 006+010 (on/off) and 012 (reg piston) 90 durometer buna o-rings (and some 016's just to pad the order out and get free shipping), bringing my grand total to something like $3 and some change.

    When I install these in their respective locations on a Classic mag running HPA, what will happen?

    1. Immediate failure. Parts simply will not seal right from the start, or deform and jump out of their seating, or whatever.
    2. The parts will work, but will crap out after X number of cycles, compared to Y cycles for the authentic parts. (Fill in values for X and Y.)
    3. I have no idea.

  26. #26
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    Quote Originally Posted by GoatBoy View Post
    To be clear: I'm not saying that urethane and buna are the same. They will have different properties. That's why I keep digging at the properties and contexts of usage.




    Well, here we have a matter of scale, which definitely matters. But if the difference between one and the other is scale -- "large" area vs. "small" area, how "small" is small? In many of these o-rings, it's arguable that the affected areas are relatively small. It's not like we're talking about solid rocket boosters or something. Instead of "small area", is there some sort of equivalent for something like Reynold's number to determine what "scale" you're at?
    There is no number to judge scale. It is based on multiple factors. How big is the diameter of the inner wall vs the inner diameter of the oring, and what is the diameter of the outer wall vs the outer diameter of the oring, and what is the height of the side wall of the groove that the oring sits in, and how wide is the groove that the oring sits in all come into play. So, unless you know those numbers for every situation, you can't determine the result. Any one of us here could accurately determine exactly the best oring for our gun setup using calipers and some time if we knew the math to go along with oring use and design principles. Some of us do know but don't care enough to use the time to save $0.25. Its not worth it to most people. And the numbers I get with my gun aren't gong to work for someone else's. We have to use worst case scenarios for generalization and factor in a bit of error. That may lead to using a urethane oring instead of a buna oring because "I know it will always work" vs "I think it will work most of the time".

    Quote Originally Posted by GoatBoy View Post
    By the way, I looked in my parts box -- the two black o-rings I saw were... TL barrel (may or may not be from AGD; I had so many parts kits that unfortunately I opened them and consolidated them), and the lower ULT o-ring, which I do know was from AGD.
    The buna TL orings are not AGD. The lower ULT oring is buna because the of the elastic properties which can seal without providing extra pressure against the pin. The buna works here because of the larger size and diameter of the oring vs the size of gap between the ULT pin and assembly.

    Another place that buna works is in the powertube for a level 10 bolt. It wears out quickly, but it works extremely well.




    Quote Originally Posted by GoatBoy View Post
    And there again I caution against the use of the word 'quality'. How do you know they're good 'quality'? Because they meet specs. Specs which are defined, quantifiable, and measurable. This is different from the warm fuzzy feeling you get from buying o-rings from someone reputable. Most people use 'quality' to refer to the latter.
    How do you buy a car? They all meet the specs in that they are legal on the road and are safe and will get you from point A to point B at the same speed. But yet, we all have our way of judging a certain quality when it comes to cars.

    I could buy my orings off some guy in china and get a good price. I am taking my chances. They may be the best orings I ever bought, or they could be crap even though they meet the "surface specs". I say "surface specs", because we are trusting that the listed specs are the ones we are getting, when in reality, it is often hard to determine if that is so unless you have expensive measuring equipment. I could go down to my local Parker oring store and buy my orings and get the same ones. I feel better going to Parker, even though I may pay more. They have an excellent reputation of delivering quality and my experience in the past has proven that. To me that's quality.



    Quote Originally Posted by GoatBoy View Post
    So let's play a game. As I like to say, the best indicator of understanding is predictive ability.

    In a totally-hypothetical-and-not-at-all-real-and-did-not-happen-last-night-at-all make-believe scenario, I hop online and buy 5 each of 006+010 (on/off) and 012 (reg piston) 90 durometer buna o-rings (and some 016's just to pad the order out and get free shipping), bringing my grand total to something like $3 and some change.

    When I install these in their respective locations on a Classic mag running HPA, what will happen?

    1. Immediate failure. Parts simply will not seal right from the start, or deform and jump out of their seating, or whatever.
    2. The parts will work, but will crap out after X number of cycles, compared to Y cycles for the authentic parts. (Fill in values for X and Y.)
    3. I have no idea.
    #3 is my answer unless you give me the the tolerances of the orings, the min and max values for impurities, and a degree in materials or chemistry to figure out how it all goes together. In reality, if you do your homework and the orings are listed with their proper ratings including tolerances and impurities, you can probably determine a pretty accurate probability of failure for each scenario they will be used in. But, that would require a lot of measuring, spec reading, and math. You can't just go by the size, type, and durometer rating. That would be like buying a car because it has 4 wheels and a motor. There's a lot more you need to know than just the size and type if you are going to step outside of the known recommendation.

    What I'm saying here is that you can't just go to billy bob's backyard oring shop and get your orings and expect that you are going to get something that will work for you. You need the real info on them which is usually only available at manufacturer sites which are often more expensive places to get the orings.
    Last edited by athomas; 04-03-2013 at 09:09 PM.

  27. #27
    Quote Originally Posted by athomas View Post
    There is no number to judge scale. It is based on multiple factors. How big is the diameter of the inner wall vs the inner diameter of the oring, and what is the diameter of the outer wall vs the outer diameter of the oring, and what is the height of the side wall of the groove that the oring sits in, and how wide is the groove that the oring sits in all come into play. So, unless you know those numbers for every situation, you can't determine the result. Any one of us here could accurately determine exactly the best oring for our gun setup using calipers and some time if we knew the math to go along with oring use and design principles. Some of us do know but don't care enough to use the time to save $0.25. Its not worth it to most people. And the numbers I get with my gun aren't gong to work for someone else's.
    And yet... you just gave a hint as to the scale question when responding to the ULT o-ring, which seems to be a problem...

    Just looking up the modulus of elasticity and shore durometer, it seems like they can be related.

    http://en.wikipedia.org/wiki/Shore_d...lastic_modulus

    I would posit that at the small scale and for our purposes, shore durometer is pretty much all you need as far as hardness/elasticity goes. And that's why it's the number that's provided most of the time. The scale I'd probably go by is in fact the shore durometer test itself is only like 1.1-1.4mm in diameter. If your affected area isn't way bigger than the test itself, intuitively durometer is probably good enough.

    Furthermore, I was searching for the ULT thing and ran across this:

    http://www.automags.org/forums/showt...212#post163212

    So AGD's own answer has *absolutely nothing* to do with any of this.


    Quote Originally Posted by athomas View Post
    The buna TL orings are not AGD. The lower ULT oring is buna because the of the elastic properties which can seal without providing extra pressure against the pin. The buna works here because of the larger size and diameter of the oring vs the size of gap between the ULT pin and assembly.
    So at this scale, or relative scale/ratio in the measurements, buna is OK. See above.

    Any ULT historians want to dig back into history and go figure out why they went with buna instead of urethane for this one? I'm digging but I can't find it.


    Quote Originally Posted by athomas View Post
    How do you buy a car? They all meet the specs in that they are legal on the road and are safe and will get you from point A to point B at the same speed. But yet, we all have our way of judging a certain quality when it comes to cars.
    Right. People have different criteria because they use their cars as status symbols. What that has to do with o-rings... somewhat debatable. Although probably less debatable now that I stop to think about it. Some people will brag about the brand of oil they put in their car. /me shrugs.


    Quote Originally Posted by athomas View Post
    #3 is my answer unless you give me the the tolerances of the orings, the min and max values for impurities, and a degree in materials or chemistry to figure out how it all goes together. In reality, if you do your homework and the orings are listed with their proper ratings including tolerances and impurities, you can probably determine a pretty accurate probability of failure for each scenario they will be used in. But, that would require a lot of measuring, spec reading, and math. You can't just go by the size, type, and durometer rating. That would be like buying a car because it has 4 wheels and a motor. There's a lot more you need to know than just the size and type if you are going to step outside of the known recommendation.

    What I'm saying here is that you can't just go to billy bob's backyard oring shop and get your orings and expect that you are going to get something that will work for you. You need the real info on them which is usually only available at manufacturer sites which are often more expensive places to get the orings.
    I'm not too shabby with math. I've been known to occasionally do my homework.

    If this is the case, there is no way to definitively answer with any parts from any source other than AGD. Not even from Parker. Same arguments apply. Not necessarily because Parker didn't provide specs, but you don't know the specs on the AGD side.

  28. #28
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    Quote Originally Posted by GoatBoy View Post
    And yet... you just gave a hint as to the scale question when responding to the ULT o-ring, which seems to be a problem...

    Just looking up the modulus of elasticity and shore durometer, it seems like they can be related.

    http://en.wikipedia.org/wiki/Shore_d...lastic_modulus

    I would posit that at the small scale and for our purposes, shore durometer is pretty much all you need as far as hardness/elasticity goes. And that's why it's the number that's provided most of the time. The scale I'd probably go by is in fact the shore durometer test itself is only like 1.1-1.4mm in diameter. If your affected area isn't way bigger than the test itself, intuitively durometer is probably good enough.
    Yes, I have to agree with you here. It appears they are closely related. The one thing that isn't listed is the effect of the type of material on the surface friction. This affects how the orings move when subjected to a compression force. So, two different materials with the same durometer rating could give slightly different performance numbers in the same place. But, overall I think you are correct in your arguments.

    Quote Originally Posted by GoatBoy View Post
    People have different criteria because they use their cars as status symbols. What that has to do with o-rings... somewhat debatable. Although probably less debatable now that I stop to think about it. Some people will brag about the brand of oil they put in their car. /me shrugs.
    Nothing to do with orings, but does have to do with the thought process we go through and the comfort we have when selecting a product using criteria we think will deliver quality.




    Quote Originally Posted by GoatBoy View Post
    I'm not too shabby with math. I've been known to occasionally do my homework.

    If this is the case, there is no way to definitively answer with any parts from any source other than AGD. Not even from Parker. Same arguments apply. Not necessarily because Parker didn't provide specs, but you don't know the specs on the AGD side.
    You and a few others are the exception in most of the forums. You can figure it out and come up with a reasonable reason why different orings can be used and where they can be used. Most can't and don't want to. Those people want a canned answer that they know will work every time without any thought. Like most manufacturers, AGD doesn't list their specs or tolerances. If they did, then they would be bound by them and that opens up additional customer service headaches.

  29. #29
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    Quote Originally Posted by Justus View Post
    A urethane 90D o-ring of the right size does not have anything magical about it just because it came in a parts kit.
    Blasphemy! Everyone knows that without the magic orings from the parts kit that the gnomes inside will die.

  30. #30
    My order of 90 Durometer Buna O-rings from Billy Bob's Taco and O-ring shack came in from China.



    I swapped out the two 006 on/off orings, the two 010 o-rings for on/off, and the 012 reg piston o-ring. Left all the other o-rings the same, particularly the LX bolt.



    So it doesn't fail immediately off the bat. Also, you'll notice now that once I hold the trigger down, no more leaks, and I never touched the LX bolt configuration. I'll be running this setup from now on to see how long it lasts.

    Per this discussion, this is obviously an "expert level" substitution, i.e. if you can tech your own stuff and know what you're doing, you can get away with it. If you ever have to send your gun in to AGD or Tuna or something and they find Buna o-rings in there, all of us are probably going to be very annoyed with you.

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