Airtighting: different materials and their effectiveness and effect on friction

[QUINCYMASSGUY]

OK folks, especially the usual crowd who always provide some great info (PBJosh, The Electrician, AThomas, Hitech, all you folks) here is something I have definitely been thinking about, especially with the ever-increasing presence of spool valves: What makes a designer choose to use a certain type of oring or other airtighting mechanism? I mean, first lets rule out some of the more common things used to prevent leakage:

Loctite, an oring around a screw, static orings like the one that goes around a tornado valve to seperate the air chamber from the hammer chamber, etc.

I am focusing on those types of sealants used in dynamic parts, like with bolts. The more friction you have, the more force you have to overcome, and you also risk early wear resulting in leakage. A good example is if you use an excessively large oring, it would either cause stick or just get shredded. Why do most pball companies choose the oring they use now instead of either a thicker or thinner one (width-wise, not diameter) and how loose of a fit can an oring have while still effectively sealing?

Delrin has become increasingly popular, but two things I've noticed: 1.) It isn't being used by everybody and 2.) alot of designers still incorporate orings in their delrin bolts. How effective of a sealant is delrin? Will it ever replace orings entirely? If it can seal well, why has the matrix not had delrin utilized in its spool valve?

Sealing the ball in the barrel from the chamber at the time of firing has been one of the biggest hurdles in bolt design, if it wasn't needed, companies could have a loose piece of delrin just push the ball in and the rate of cycling would be insane. Timmy's get close but still need the seal. What are all your thoughts on the different methods of sealing parts used in dynamic movement and what is the optimal methods? pros/cons?

[pbjosh]

Delrin isn't really a sealant.

Why you see delrin in bolts today is a combination of weight, oiless operation (not self-lubing) and hype.

Alot of hype.

Delrin does help lower the weight, while maintainng a smooth seal. But a delrin bolt is suppose to provide a tolerence fit to seal well without o-rings. To do this the tolerence needs to be about .003" between the bolt and the breech. To tight and it isn't smooth, to loose and it doesn't seal.

If a true tolerence fit is built, then having no o-rings on a bolt is fine. BUT- To compensate most bolt manufactures put o-rings on. And then, only on the back end, allowing for blowback in the tip.

Most bolt designs simply are not built well. Using the right materials, but the wrong application of them.

To get the tolerence fit a design also has to include the difference of something as small at the annodizing diff from gun to gun. Not all are built the same. So getting a tolerence fit is hard, but not outside a companies abilities.

I chose not to include all delrin seals (no o-rings) in the Shiva actuating parts for several reasons. I am using a tolerence fit bolt and powertube though. Since the air travel in those areas is in the 5-10ms range I am not worried about leaks.

In the actuating parts the delrin would scratch, loosing the seal. Since the the internals needs to hold the seal for several minutes, even hours or days, a tolerence fit didn't seem appropriate. O-rings can fill in the grooves produced from long time wear. This will mean the internals will have a much longer life, and lower failure rate. And due to my design the removal of movement o-rings takes seconds. So keeping them seems the right thing to do. And replacing a couple o-rings is simpler than replacing a central piston shaft.

In some portions of each marker delrin could replace o-rings, but not in areas the have a static seal for large portions of time. Take the valve in a cocker. While a delrin valve, if made PERFECT, could seal just fine for short peroids of use. It would have residual leakage though over a period of time. With an o-ring, none.

And Delrin is not some strange magical product. If an aluminum bolt is built to the same tolerences it will seal just fine. I have seen them before and they work very well. No o-rings, just a tolerence fit.

Josh

[QUINCYMASSGUY]

delrin

Thanks for the info on Delrin, I guess what got my thought going on that one are the newer WGP Orracle bolts with delrin but no orings and alot of timmy bolts, that both seal but only use delrin. The blowback doesn't seem bad either meaning little air is leaking out around the bolt when it's sealing the ball in the barrel. The ideal bolt would be one almost weightless with absolutely no friction. I'm suprised more haven't taken the idea of the angel bolt which has got to be the smallest, lightest, and I don't believe utilizes any orings and I guess seals pretty well. What are your thoughts on this bolt compared to one such as the aluminium lightning bolt with orings used in autocockers and timmy's?

Alright, back into the lab to do some brainstorming....

[pbjosh]

My ideas on bolt design came into action with the Deviant:

http://itspaintball.com/page5.html

The internals need a bit of work, but for the most part I think it is nearly perfect.

It falls out the back of the gun, NO friction at all, but the seal is so good you will pop you eardrums before you hear a leak, and weights about 1oz, nearly 1/2 the weight of the WGP bolt.

I might be bias, but I also might be right-

Josh

[QUINCYMASSGUY]

impressive

Very impressive, I am dying to see your shiva in fine detail but totally understand why you're not giving exact specs away right now. I am cooking something up but has some ways to go, it's actually 3 ideas in one involving tolerances as your bolt does, and I guess a major component is using reliable seals that provide minimal friction. So delrin did work for you, or did you use the same idea with metal? How long are you keeping the bolt, and is the spool technically part of the bolt row like a Matrix or in the tube below like a Cocker?

Now here's a new question: orings can usually hold a limited amount of pressure, how does Delrin compare for this purpose? If it's used for bolts, it has got to hold air pressure better than orings do. Is this true?

[painTech]

well delrin is obviously stronger. orings just expand like a ballon when air pushes at them. making them idealfor seals.

[athomas]

The choosing of an o-ring is much more complicated than many realize. O-rings can take up any tolerance issues between parts, especially if they are to act as a seal to hold back air. Many manufacturers use them for just that. Instead of precisely machining the inside diameter of the tubes and outside diameter of the parts, they leave a bit of a gap to ensure a fit no matter what. They let the o-ring fill the gap. The problem with this scenario, is that an improperly fitted o-eing can jam the device. We see this with many markers having first shot drop-off. I'm sure there are many instances of improper use. The manufacturers use special lubricants to help overcome the friction but its still there.

The ideal o-ring situation is to keep the area of contact during compression as small as possible. Too much gap between parts means too much o-ring gets jammed into the void. This usually means a larger flat surface of contact which results in more friction. Ideally, we want to use the smallest o-ring that will work in the situation. The groove that it sits in has to properly fit the o-ring that it is to hold.

The o-ring when properly used is very valuable because it makes a replaceable point of contact. It is usually softer than the material it is rubbing against so it wears out instead of the part. Most o-rings are only a few cents to buy so it makes economical sense in the protection and long term use of the device.

[QUINCYMASSGUY]

Athomas, excellent post. You addressed a couple things that were the main drive behind this discussion:

Imagine a Matrix with frictionless seals: No FSDO, even lower operating pressure.

Imagine a Lvl 10 where an extremely loose oring was used that resulted in no friction but never leaked: much better cycling and no risk of stick (which I used to get alot causing the bolt to not go back fully and not allow the sear to reset. Yes, I did lube it.

Imagine a bolt that could just slide freely back and forth, little if any inertia involved while still maintaining a full seal between the air passage into the bolt and into the barrel. The cycle rates would be beautiful.

These are all the reasons orings are annoying, and I know Tom Kaye wrote a whole article on how annoying they are, mostly due to tolerances in production being so variable. But how orings can have intentional variability to always provide a seal is a good reason why they remain.

Now imagine a bolt of delrin with an oring around it (for example, a WGP bolt with the three orings). Could the bolt be to a very close tolerance, and then use an oring so embedded in the bolt that only the absolute tip touches the side? It seems most bolts allow more of the oring to seal against the side than they need to. Cutting the area left on the sides of a bolt to allow tolerance differences is important, but it seems alot of manufacturers leave too much up to assuming they'll produce a bad product.

So I guess my question here is: which bolts right now allow for a constant, reliable seal yet maintain the maximum fluidity and minimum of force to get it in motion? What makes them so special?

What about a delrin bolt for a gun that is actually designed to be a tight fit in a gun but, by cycling at a high pressure, the friction polishes the sides until it is a perfect fit then the user drops the cycle pressure down? Has this been utilized at all? Delrin or another slick material that the aluminium could hone down while cycling would be ideal. The bolt should initially be +.01 at most if possible but then the polishing would fine tune it to the specific gun.

[pbjosh]

The problem is-

While a tolerence fit, even a tight one, would be smooth, it would still leak.

Sure, .003" is a small, small difference, compared to a N2 molecule it is a huge gap.

SO- you WILL leak. Just not very fast.

With an o-ring- Not at all.

And FSDO is also an affect of the o-rings in the Solenoid valve.

A tolerence fit is not a pressure seal. It works for 5-10ms, even in 1 second you won't leak to much, but you WILL leak. Hence, the wide spread use of o-rings.

Josh

[QUINCYMASSGUY]

tolerance

Your last statement there got my attention: 5-10ms is the time it takes to fire a paintball so technically all-delrin bolts can work, and if leakage happens it will be almost negligible. And if a very light oring seal could also be used, it might be enough to prevent even that little amount.

So now the next question in regards to seals comes to flow rate of air: you have all the talk of larger gauges being used, be it cocker rams (SMC rams bored out to allow more air flow through the airlines into the chambers, larger valve openings like the tornado valve, etc. I guess my question is, is there a question to determine that based on a.) the pressure of the air on one side of the seal b.) the pressure of the air on the other side of the seal c.) the size of the opening and d.) how much room the air has to flow into and whether that area is expanding (in the example of a paintball making its way down a barrel) what is the rate of speed that air can flow? This almost relates to recharge too, if a valve opens X amount, it needs Y amount of time open to fire the gun, but if it is open X2 amount, it needs Y2 amount of time open to properly fill the area behind the ball to fire it. This definitely has implications in HP vs. LP operation, if the pressure is at 200psi and the ball requires 75psi, the time for the 200psi to expand out to a larger 75psi area is greater than it takes 400psi, like a mag, to expand to 75psi because the volume of that pressurized air that needs to go through for the LP gun is much greater than the 400psi.

2ci*400psi=10ci*80psi so only 2ci have to flow through the valve to fire, meaning short dwell time
4ci*200psi=10ci*80psi so twice as much must get through the valve, meaning longer dwell time

So if a valve for a 400psi chamber had a flow rate of 1ci/sec (odd number, just proving an idea) that means the valve would have to be open 2 seconds to release the appropriate gas. A 200psi chamber would have to be open 4 seconds to release the equivalent amount of gas.

So.... based on the orings wouldn't a Low Pressure gun's chamber leaks release far less air than in a High Pressure gun's chamber? How much effect does the pressure have on how well the orings seal or whether or not delrin would be better at sealing a space for a 400psi chamber rather than a 200psi? Let me know if you need that rephrased

[athomas]

Re: tolerance

Originally posted by QUINCYMASSGUY

So.... based on the orings wouldn't a Low Pressure gun's chamber leaks release far less air than in a High Pressure gun's chamber?

Lower pressure = less per time, but a longer time.

200psi for 4 sec at X psi/sec = 4X leakage
400psi for 2 sec at 2X psi/sec = 4X leakage

There will be some differences because of other inefficiencies but the leakage at different pressures will probably be close enough to be called equal. Any leakage will be a resistance at any pressure so it shouldn't be a high flow area.

The trick would be finding, as was mentioned, enough of a seal to effectively block the flow of gas, without providing any friction to the bolt action. If 99.5% of the gas goes out where it is supposed to, would it be considered acceptable. The mag and many other guns had considerable blowback at one point in time. I bet that the gas that was lost in directions other than out the barrel pushing the ball, was quite high. Its something to think about, that's for sure.

As to an o-ring deforming vs pressure, that's a very good question. A stiff o-ring will maintain ridgidity at lower pressures and may require a higher pressure to properly deform to fit any minor imperfections. A loose or soft o-ring may deform too much at a high pressure and increase the surface area of contact or deform to the point of allowing an air passage past a deformed surface.

[pbjosh]

athomas~

You nailed the 'New' WGP bolt O-rings right on.

FINALLY a company puts a soft enough o-ring on the bolt! One that shows very light friction against breech and soft enough to actually move and seal in the breech underpressure. But there is no seal on the tip- allowing blowback from there. It is .683" in dia- alot better than the .679"-.680" in the stock bolt (and superfly.) The Deviant comes with tips that are .684", .685", .686", .687" to compensate for the exact fit to your breech. And the bolt design I have for the cocker does seal perfectly. It doesn't have any o-rings.

If I tried to seal any sort of pressure with the Deviant bolt, for any time longer than a few millisec, I would find it leaked ALOT.

Delrin will seal only for a SHORT TIME-

Any long time seal WILL leak.

Maybe not much, but setting your gun down for 15 minutes would mean an empty tank. Have you filled up right before a game and then waited 15 minutes to start? You might be out of air.

QUINCYMASSGUY~

To get a delrin bolt to work requires a tight tolerence. Most do not. In fact Dez and the Deviant seem to be the only bolts that can do that. Most of the others are SO badly built. My input to Rocky Knuth went to WGP, hence the larger .683" dia bolt. Or else it would have been .680", with alot of tip blowback.

I built the Deviant because I couldn't find anything else that FIT- without making a custom order.

And that is just the bolt. Not anything internal. A good bit of leakage is had from 5-10ms of operation with most of the delrin bolts made! Imagine that with the seals on the Matrix! Ouch!

I found this little bit on O-rings and fit:

http://www.molconwell.esmartweb.com/o-rings.htm

http://www.usseal.com/orings/oring_function_1.html

Josh

Edit- There is a good chance that the WGP bolt o-rings will act like the first diagram in the usseal.com link in a larger breech.

[QUINCYMASSGUY]

quality vs. price

I think both of you have addressed very good points, but allow me to throw in yet another: is it worth such fine detail? Yes, it has benefits, I'm not ruling that out, but such fine detail that the fit consistently fits the extrememely tight specs has got to take a.) very expensive machinery b.) insane amounts of work-hours or c.) alot of trial and error with any items that are even slightly off having to be further modified or, if that is impossible due to too much being taken off, scrapped. I think alot of companies weigh this all in and, when it comes down to it, would rather save a ton of cash and go with a tighter, less effective oring fit or allow minimal leakage. Or in the case of some companies they are just lazy people with no attention to detail or interest in using QC to produce quality products. Also, certain types of markers may require less attention to fine detail than others. I bet an open bolt blowback requires the least attention to detail which is why you have 32 degrees, Kingman, and such focusing entirely on them instead of more advance markers like vikings, angels, timmys, etc.

So here's an interesting point: Mags have absolutely no orings on the bolt so does this mean they are far more susceptible to blowback than most other markers? I think they are, and seems to be something that would definitely contribute to inefficency. What if they had an oring down at the base of the bolt, around the little lip that the sear holds (implied that it should be set up where the sear won't press against it and break it) so that upon the point of firing, a rubber seal exists that should reduce blowback, requiring less volume of air to fire since less would be wasted, hence increasing efficiency. I think Smartparts might have basically patented that though (and no, not joking, it is called "sealed bolt technology" I think), so AGD would be careful about using it since even if it's b.s. that it can be patented, the same could be said for the e-marker deal.

A soft oring definitely seems to be a good idea, reducing friction, except for the leakage issue since a ball firing would definitely require high pressure. However, if the delrin provided the majority of the seal and a soft, loose fit oring finished the job, that could work. Also, what if the bore of the top tube tightened up just minimally at the front so the bolt can move freely up to the point of firing where it gets that minimally smaller bore and seals right.

OK, that's all I got for now, but I'm sure more thoughts will be brewing soon.