Quote:
Originally Posted by Hooked_on_Paintball
no, a little bit of LocTite is needed.
remember, the tank is under EXTREMELY high pressure, and you are screwing it in and out of your marker. You dont want to screw out hte reg do you?
just add a small amount of loctite.

Well don't forget now that the tanks have about 4500 psi in them....That's 4500 pounds per square inch.
Now you look at the approximation that the first three threads carry about 99% of the load on anything and look at a healthy worst case assumption of maybe a half inch threaded diameter and a thread depth of maybe 0.0625 inches (1/16th):
pi*r^2 = area of circle, there are three circles so:
pi*(0.25^2  (0.250.0625)^2)*3 = 0.2577 in^2
0.2577 in^2 * 4500 lbs/in^2 = 1159.65 pounds of force upward
however you gotta look at the fact that the threads are on an angle, so making an assumption that the threads are 30 degrees off of the horizontal:
1159.65*cos30 = 1004.28 lbs vertically on the threads
then of course you have to think about the friction in the other direction:
the friction coefficient for aluminum on steel (I'd assume the aluminum reg screws into steel? either way this friction coefficient is lower than aluminumaluminum) is 0.61:
So the friction force parallel to the threads would be:
1159.65*cos30*0.61 = 612 lbs
Now subtract the force in the horizontal from the tank pressure:
1159.65*sin30 = 580 lbs
Overall, using some pretty bad assumptions, you'd need to have at least 30 pounds of turning force to unscrew your reg fully pressurized. But this is neglecting the friction seen by all of the other threads, assuming that the threads touch the tank only on one side.
However tightening the reg down to "hand tight" (having the reg slightly torqued so that it sticks, or now assuming the upper and lower threads touch the mating areas completely even though if I recall correctly it's really NPT threads are tapered so when one screws them down the female shrinks and the male increases in diameter until they join):
(5/3 is assuming the upper two of the bottom three threads are "pinched" allowing double surface area contact on them)
(5/3)*1159.65*cos30*0.61 = 1021 lbs
Now one is looking at about 400 pounds to unscrew the reg.
Ifsofacto I'm basically trying to say that you shouldn't really need to worry about "accidentally" unscrewing a HPA tank from its reg when pressurized.
I did this rather quickly and made some assumptions so there could be a few mistakes and anyone is welcome to challenge me on the subject.
Lol I could go into it more but I'm supposed to be researching macro fiber composite applications right now