To vent an empty CNG cylinder?

Does anyone knows how to vent an empty CNG cylinder?

I unscrew the inlet valve and fill it full of water, but the person who will cut it says that this is not enough.

It seems excessive to me, but...

Thanks in advance!

sort by: active | newest | oldest
Kiteman5 years ago
The person who will cut it is being paranoid.

Tell him to grow a pair and get cutting.
rimar2000 (author)  steveastrouk5 years ago
rimar2000 (author)  Kiteman5 years ago
Yes, Kiteman, I think the same thing. Think the truly problem is not fear, is lack of time for little works: the owner of the workshop has too much work to do for companies, and he can't charge to me much money.
AaronAllen14 years ago
CNG is lighter than air, the venting would create a "torch" effect, burning directly upright for a few brief moments until the gas has dissipated. Do it a bit carefully.
American CNG
AR10NZ5 years ago
Hi Rimar :
How are you ? We are boxing on OK here in NZ. Latest project is a suppressed over Bbl unit, for a Ruger 10/22, for a friend. Using 19mm titanium tubing, very light weight, and very quiet., functions well with subsonic ammo.
Re : CNG cylender, I have gas cut 1 with no problems, but in the past, have modified gasoline tanks , cutting & welding, etc, using compressed air, introduced to the bottom of said vessel, to dilute & expell volitiles.
rimar2000 (author)  AR10NZ5 years ago
Tnanks, AR10NZ. The cylinder is now at the workshop, waiting the time (and will) to be cutted.
pfred25 years ago
He means you're not paying him enough. You have an angle grinder. Get a cut off wheel for it and do it yourself.
rimar2000 (author)  pfred25 years ago
Fred, I can stand a month to cut the cylinder with grinder. It has steel walls, 1/2" thick. Now it is full of water since saturday, today I will try to cut a groove to show that is possible and safe. I hope the worker will do the work for me, and he will not charge a lot for it. He is the same person that cut the rail for my anvil.

Here in Argentina the government is removing fuel subsidies, bringing the price of natural gas will increase greatly. A salamander can be fed with any garbage that can burn, making it an interesting project. I have time, because it's hot here yet.
How do you know it is 1/2" of an inch thick? You drilled into it? When I cut a cylinder in half I found out in the middle it was only half as thick as it was on the ends. I think they are that way because of how they are made.

I look forward to seeing your salamander project. Here winter is ending, I hope!
rimar2000 (author)  pfred25 years ago
Years ago I saw such a cylinder, which had cut a piece to show the thickness of the walls, and they were really thick, 1/2"or more. It is true that it was a 65 liters capacity, and mine is 30, but I guess it should have very thick walls too. 3000 PSI is a very great pressure to bear, and the 5 years safety tests are done at 4500 PSI!!

Today I was doomed to other tasks, but in the afternoon I will try to make it a cut for to out of doubt.
Maybe drill it?
rimar2000 (author)  pfred25 years ago
Yesterday I did that groove, and using a wire i measured the thickness of the wall, it is 1/4 inch. You are right, 1/2 inch is only for biggest cylinders. I welded a handle at the bottom of the cylinder, and put a short iron tube at the other to enable to manage it. Today I carried it to the workshop that will cut it. I marked the lateral door and the holes at the ends.

It is really hard!
If you think about it it makes sense. Every cylinder deals with the same pressure per unit of measured area (pounds per square inch) but a larger cylinder has much more area (many more square inches) than a smaller one. These all add up like weights. What is worse is the larger cylinder has that area spread over a longer distance too, like a long beam. So just like long beams bigger cylinders must be much thicker than their shorter counterparts to bear the same loads.

All of that is why the little tank has much thinner walls than the big tanks do. But it is just as strong.
rimar2000 (author)  pfred25 years ago
Certainly, it is so. The little tubes that convey the gas from the cylinder to pressure regulator have only 1mm thick wall, and they resist very well.
Lines away from tanks often are not under full cylinder pressure, but a reduced, regulated force. Still, you are onto something there.
rimar2000 (author)  pfred25 years ago
Passing the regulator, the pressure is very low, maybe around 10 PSI.
I was thinking you could have built a fire then put the tank on it, and let the fire go out and annealed it somewhat. Seemed a bit extreme to suggest to me so I didn't. Probably would have softened the metal though.
It will be fine after being filled with water. I've done several after this treatment. There is no problem.

rimar2000 (author)  steveastrouk5 years ago
The cylinder is stiil empty with water. Tomorrow I will try to cut a groove (crack?) at an end, to show him that it is safe. The work will be quite a while, using my little hand grinder.
rimar2000 (author)  rimar20005 years ago
When I wrote "empty" I want to say "full".

Pardon, my English is terrible.
irteachre5 years ago
Why vent it if it's empty? Don't drill or cut it unless you know for sure that it's empty.
rimar2000 (author)  irteachre5 years ago
Normally fuel containers are very dangerous to cut, to weld, etc. There was many deadly accidents due to this. In this case, I think the worker is only saying excuses.