O-Ring Grooves

Apples and Oranges.  You are seeing the difference between pneumatic and fluid engineering. Air being harder to keep sealed.

tallen702 wrote: Liquid FTW!!!!! Pneumatical dymanic engineering and fluid dynamics are completely different. So the o-rings need to do different things. A loose o-ring would let air through, even in minute ammounts, which is a bad thing when you're trying to get a tight seal. A loose/sloppy o-ring will also experience more wear and tear when being subjected to the rapid movements that such seals encounter in paintball markers. They're the same principal applied to two different sciences.... Using a plumbing o- ring on a pneumatic system would be like using expoxy on you're marker's screw threads instead of loc-tite.

I was totally gunna say that exact stuff.

O_o

Bah, let me retype this sentence...

When the two mating parts that the o-ring is sealing between are engaged, the o-ring is compressed which flattens it out into a more oval shape taking up much of that groove.

Okay, couldn't think with all that stuff going on in the office yesterday. Anywho, I mis-spoke when I said fluid dynamics as you are indeed correct that it includes gasses, I should have said Hydrodynamics. Anyway, on to the point. Why are the o-ring grooves in paintball markers and parts machined without the usual gap-space that you see in more industrial or hydraulic applications? The first reason I can explain is that you are working with an open-circuit continual-use pneumatic device. Basically, you have gas that is moving from one point in the system out into the atmosphere. This is important to remember because if you have a lot of drag on an o-ring (either caused by the necessary pressure to force the o-ring into an oblong shape to fill the gap, or by lack of said pressure and only the o-ring is allowed to "bounce" around in it's gap) the seal wears down signigicantly faster. The way you get around this is by using lubrication. For the best lubricant for rubber is water. However, water and paintball don't mix too well. The fact that it also evaporates from an open system rather quickly (depending on relative humidity) means that you'd be spraying your o-rings down rather frequently in game to keep them lubricated. So, we use specially manufactured lubricants (usually synthetic oils) to lubricate our seals in our open ended pneumatic system. This lubrication, however, is subjected to a one-way airflow that vacates it from the system in considerable ammounts every time the system is cycled. Thusly, to lower drag between parts and thus save wear and tear on the seals as well as allow the marker to cycle in an efficient and quick manner.

The other consideration is that when manufacturing parts for paintball the tolerances must be a little looser than a system that is set up for continuous use in a specific environment. Paintball markers are subjected to sand, dirt, water, gelatin, paint, severe temperature changes, and a range of pressures. The looser the tollerance, and thus, the more space between moving parts, the more punishment any given marker can take with less breakdown and wear and tear. Compare an AK-47 with very loose tolerances and the M-16 which was machined to very tight tolerances and specifications. The AK takes far more abuse with fewer maintinance issues than the M-16 does. Of course, both systems run perfectly well when kept and maintained properly, but the looser the tolerance, the more abuse it can take without seizing up.

Of course, there are examples of paintball markers with parts that DO have room for slop in their o-ring grooves. The hammer o-ring on a tippmann 98 has quite a bit of slop in it, it also tends to wear down far more quickly than any of the other o-rings or seals in the marker that move just as much. My Palmer's quikswitch also uses a large o-ring groove in it's construction, it too has worn much more quickly than any of my previous 3-way valves that had less of a gap and much tighter fitting o-rings.

The pressure needed to compress the o-ring between two metal parts is simply a detracting factor when it comes to the high-speed cycling rates needed in today's paintball markers. Remember, some of these markers fire faster than the fastest SMG's available to any country in WWII and every bit as fast as the German MG34/42's and faster than any conventional machinegun used in the modern military (with the exception of mini-hawks, "chainguns", and the metal-storm weapon system.)

I hope this helps to answer your question.
Just remember:

Drag
Tolerance
Cyclical ROF
Lubrication

The 4 biggest limiting factors of seals in paintball.

no problem, as far as lubrication is concerned, we're finding that more and more markers are having to use more specialized lubrications rather than the typical "gold cup" oil, or Hoppes No9 that we've all been using for years. I find a lot more white lithium grease in markers these days, especially the electro pneumatic markers that are solenoid driven and that tend to operate at extremely low (for paintball standards) pressures. Your electro pneumatic markers are also coming with tougher tolerances. The matching between bolt and breech is getting to the point that on some markers (the Dye Matrix series DM3 through 7 for example) that the machinists and engineers are having to come up with ways to minimize the damage that the moving parts are causing. The breech in the DM series is being changed in the upcoming DM7 to one that has something like a lexan sleeve that protects the metal and is replaceable when it wears.

Glad I could be of use! My dad is an engineer and I worked as an airsmith for several years while in college, but that was over 5 years ago. I know how things that don't seem to fit will nag at your attention until you figure it out.