TargetTalk

Plasma Cutter?

Next time use a petroleum based high pressure grease on the thread.

I assume you are holding your mouth right.

BEA wrote:Next time use a petroleum based high pressure grease on the thread.

No way. Petroleum based lubricants can and will degrade o-rings and other seals. Synthetic lubricants with PTFE are recommended.

Rover wrote:Well, northpaw, you were right. Even though I once owned a CPM1, I was thinking of the CP series with the hex on the end of the cylinder (not a bad idea!).

Did you TRY whacking it?

Owned once an even older Walther CO2 gun vith hex "knob" at the end, and a wrench, with a large black plastics handle, supplied.

Nope, I did n`t whack it, just applied more torque (got two strong hands...).

Wish you too a happy new good year, "Rover", hope you may achieve increasing scores with your guns during the upcoming year.

Growl when you're twisting it. Works for me!

Wile E Coyote wrote:Strap wrench?

Probably not enough clearance if the barrel is still on.

Shoot the pistol down to yellow zone, can't remove cylinder.

Shoot the pistol manually, just air out to get down to no pressure, can't remove cylinder.

Took the barrel shroud off, can't remove cylinder.

Two hands, thigh grip, no go.

Used smallest strap wrench. It is still too thick. Pushed it in, it was spreading the barrel and cylinder apart, cylinder is still no go.

More cursing, more cursing.

Finally, took the barrel off.

Finally, cylinder unscrewed.

Tested it on and off a few times. Nothing unusual. Interesting to note that you CANNOT over tighten it. You just can't. You screw it on until a constant place, and it just stopped. Every time it will just stop at same place. Whether you apply a lot of screw in pressure, or very little screw in pressure, cylinder just stop at the same spot.

So lesson learned = you can screw cylinder in with gentle force. Once it stop, that is it folks, can't screw it in any further even if you apply force. No no need to apply more force.

With the cylinder finally off, did you notice any damage or wear and tear on the male or female threads?

200 bar will stretch the threads very slightly (elastic not plastic deformation, I was a Metallurgist in an earlier life).
If the end face of the cylinder is tightened up to the face of the regulator then when the pressure drops causing the threads to relax (elastic remember) this movement is sufficient to increase the pressure between the two faces thereby increasing the torque necessary to rotate the cylinder. So over tightening in the first place causes your problem.
I hope that makes sense.

1) no apparent irregularity of threads. But if there were, what can I do?

2)plastic deformity absolutely makes sense.

seamaster wrote:1) no apparent irregularity of threads. But if there were, what can I do?

2)plastic deformity absolutely makes sense.

Elastic not plastic. Plastic deformation will not return to the original size when the stress is released, elastic deformation will. That is why bolts have specific torque limits specified, which also depends on any lubrication on the threads.

I have noticed the cylinder being harder to unscrew as the pressure drops but never realized why. But it has always come off because I do not put it on very tightly to begin with.

Something akin to a barrel vice with fitted jaws might be needed. I have used never cease on the threads too, but very sparingly. As a poster stated earlier, petroleum products are not for the plastic or rubber parts.

Happy New Year everybody!

Brian is spot on!

When you screw with 200bar in the cylinder the stud connector is under tensile force of about 628kg (~700lbs) assuming an internal diameter of the cylinder of 20mm (.78").
If the pressure goes to zero, the stud connector would shorten back to its initial length (I.e, elastic strains will be recovered) provided you left a gap to allow that. However if you tightened untill contact between cylinder and pistol frame the stud connector cannot shorten back to its unloaded length as the cylinder walls are much stiffer in extension and will impede that, hence the cylinder will be pushed against the pistol frame with about 600kg.

Aluminium on aluminium friction coefficient is extremely high if not lubricated, up to 1-1.3!!! So the friction force will be about the same, i.e. 628kg. This means that you'll have a torque of about 628x0.020= 12.5kgm to unscrew it!!

If lubricated the friction coefficient drops to 0.3 and you will be able to unscrew it.

therider wrote:Happy New Year everybody!

Brian is spot on!

When you screw with 200bar in the cylinder the stud connector is under tensile force of about 628kg (~700lbs) assuming an internal diameter of the cylinder of 20mm (.78").
If the pressure goes to zero, the stud connector would shorten back to its initial length (I.e, elastic strains will be recovered) provided you left a gap to allow that. However if you tightened untill contact between cylinder and pistol frame the stud connector cannot shorten back to its unloaded length as the cylinder walls are much stiffer in extension and will impede that, hence the cylinder will be pushed against the pistol frame with about 600kg.

Aluminium on aluminium friction coefficient is extremely high if not lubricated, up to 1-1.3!!! So the friction force will be about the same, i.e. 628kg. This means that you'll have a torque of about 628x0.020= 12.5kgm to unscrew it!!

If lubricated the friction coefficient drops to 0.3 and you will be able to unscrew it.

Fortunately its nothing like as high, the pressure effectively bears on the area of the stud connector, not the area of the end of the cylinder, this is one of the reasons the stud is designed to be so small, and usually with a reduced tip to the stud.
Also only the engaged threads of the stud will stretch, actually I think they would be in compression.
There might be some other effects, like the end of the cylinder deforming a bit as the pressure reduces, helping clamp the cylinder to the gun.
There's no need to have the cylinder tight against the gun, except for stabilisation against vibration and knocks, the air seal is taken care of between the cylinder and the stud.

JamesH wrote:

therider wrote:Happy New Year everybody!

Brian is spot on!

When you screw with 200bar in the cylinder the stud connector is under tensile force of about 628kg (~700lbs) assuming an internal diameter of the cylinder of 20mm (.78").
If the pressure goes to zero, the stud connector would shorten back to its initial length (I.e, elastic strains will be recovered) provided you left a gap to allow that. However if you tightened untill contact between cylinder and pistol frame the stud connector cannot shorten back to its unloaded length as the cylinder walls are much stiffer in extension and will impede that, hence the cylinder will be pushed against the pistol frame with about 600kg.

Aluminium on aluminium friction coefficient is extremely high if not lubricated, up to 1-1.3!!! So the friction force will be about the same, i.e. 628kg. This means that you'll have a torque of about 628x0.020= 12.5kgm to unscrew it!!

If lubricated the friction coefficient drops to 0.3 and you will be able to unscrew it.

Fortunately its nothing like as high, the pressure effectively bears on the area of the stud connector, not the area of the end of the cylinder, this is one of the reasons the stud is designed to be so small, and usually with a reduced tip to the stud.
Also only the engaged threads of the stud will stretch, actually I think they would be in compression.
There might be some other effects, like the end of the cylinder deforming a bit as the pressure reduces, helping clamp the cylinder to the gun.
There's no need to have the cylinder tight against the gun, except for stabilisation against vibration and knocks, the air seal is taken care of between the cylinder and the stud.

You are right about the cross section area of the stud only. But I think you aren't about only the threads being engaged. Once screwed in, the chamber in the frame is loaded.

nn wrote: Did you try whacking it off?

Wouldn`t do that to any compressed air cylinder.