[jeckardt]

Does anyone know the material thickness used in the Accucraft butane tanks (specifically the mogul tank)? Is there enough meat there to take a 10-32 or M5 thread? (I'm considering a tank extension, but don't want to start drilling into the tank until I know it will work.)

Thanks,
Joe

 

[Kovacjr]

Since the mogul tank os square you can see the 2 U shape parts soldered together. I would not make an extension that is not soldered though. I've seen some plumbing end caps added soldered to tanks in the past. You also need pipes to your 2nd tank if it is remote, a liquid flow and gas flow.

 

[steamboatmodel]

If you do make any modifications to the tank, it should be hydro tested to 350psi before it is used.
Regards,
Gerald

 

[jeckardt]

Actually it's the tapping for the transfer lines to the auxiliary tank that I want to make sure I have thick enough material for. I'm looking into using a Beswick double-shut-off quick disconnect mounted directly into the wall of the existing tank, with a feed line running back to the new auxiliary tank in the tender. That way I can safely disconnect for separating the tender/engine for servicing.

I have no plans in adding volume to the current tank; just adding the auxiliarly tank.

Thanks,
Joe

 

[Kovacjr]

Will the remote tank have a seperate filler and valve? With just one line you wont get the 2nd tank filled withoug a balance pipe. When the tank is filled its liquid, the lower pipe will allow liquid to bqlande between both sections, the upper one will allow gas to vent into the section or tank with the metering valve.

I dont think a tank with a disconnect will do anything except have 2 seperate tanks. Maybe put a disconnect on the jet pipe and on both tanks, then when the one runs out just switch disconnects on the tanks.

 

[Ed Hume]

Joe,

There is nowhere near enough metal in the typical tank thickness to support sealing threads. The usual practice for a pressure vessel is to machine a larger bushing with the threaded hole, and solder the bushing in place. You have to take safety very seriously when messing with pressure vessels such as butane tanks and boilers. You should not modify the butane tank with your present level of knowledge. You need to understand what the earlier reply about testing the modified tank before using really means and what that implies. You would need to have machined plugs, a decent pressure gauge and water pump to conduct that testing and you should not shrug it off. I have tested my own butane tank to 400psi. Once you cut into that tank, I don't want you near me at a steamup unless you have proven that it is safe.


Ed

 

[jfrank]

I dont want it near me either Ed. Leave the tank alone or have a specialist make you a new one that is bigger.

 

[jeckardt]

oh, well... it was a thought. Forget I mentioned it.

 

[jfrank]

Joe, don't go away mad. I mean Accucraft was so worried about this that they recalled all their K28 tanks and replace them because they didn't pass some extreme test. I know some have documented rupturing their K27 tanks by putting water that was too hot in the tender around the fuel tank. Some countries, I believe, require these tanks to pass what I would call extreme tests. The problem is in the real world, even though the instructions say use butane only, people will put all kinds of fuel mixes in these tanks and subject them to pressures they are not designed for. You may not of course. But, if you have this tank in the tender and put warm or hot water around it on a cold day, the fuel pressure goes up very quickly. If there is a weak point it will definitely rupture.

 

[Guest]

Actually it's a very good thing that you mrentioned it. Perhaps a few people who previously didn't know this could be dangerous now know why not to do this. I think John is right. Live steam is becoming more of a "consumer" hobby and you just never know what some of those nutty consumers are going to do next.

 

[Guest]

Well this is not really rocket science but it is getting close... as in the one that blew up on the pad.

Worst case the room is on fire, the butane tank is not the main problem . . . RUN!

Second worst case a tank sourounded by water at max. temp. or 100 deg. C.
This can and has been done!!
For a butane only tank the pressure can be found at:
http://www.s-ohe.com/Butane_cal.html
for conversion from mmHg to Psi:
http://www-users.med.cornell.edu/~spon/picu/calc/pressure.htm

Answer: vapor pressure of butane @ boiling point of water = 223 psi

Now assume an unknown amount of propane is added to the mix.
well I do not know how to do that so lets look at propane only:
http://www.s-ohe.com/Propane_cal.html

Answer: vapor pressure of propane @ boiling point of water = 624 psi.

NOW factor in a standard engineering safety factor of 4 and use strength of material to calculate the thickness of the tank and factor in the strenght of the joints.

In other words you need an engineering background to properly design a pressure vessel or at least understand the rules and know how and why to apply them.
Cheers Dan

 

[weaverc]

Joe,
Why don't you just purchase a second tank from Regner, Roundhouse or Accucraft? They all have various shapes and some already have valves attached. You could plumb it to a T-fitting and place the tank in the tender if it doesn't fit where it is now. Or if you buy a larger tank, you could replace the first one. Just a thought.....
By the way, Roundhouse http://www.roundhouse-eng.com/ satates on their web site that their tanks are safe for a butane/propane mix. They say "All are capable of holding butane, iso-butane or butane/propane mixed gas in an operating temperature up to but not exceeding 65 degrees celcius."

 

[steamboatmodel]

Joe,
Here is a link that shows the Pressures/Temperatures of propane/butane mixes;
http://www.engineeringtoolbox.com/propane-butane-mix-d_1043.html
As you can see from the charts it is the Propane that can cause the problems, at 100deg.F with 30% propane the pressure is 3X that of straight butane.
Regards,
Gerald

 

[Havoc]

Maybe that's why they call it a butane tank and not something else?

 

[Guest]

Carl,
I went to the Roundhouse site and did not see the 65 deg. C. figure. As this is about 150 deg. F. I agree that that is a prudent design figure for butane, propane or a mix.

It is NOT okay to use mixed gas in older Roundhouse models.
If you click on the TECHNICAL link on the mixed gas FAQ you will see the models that mixed gas is not to be used with.

I asked about hydro pressures for butane tanks several years back on a several forums including the G1MRA yahoo site and NO ONE would answer the question as to why the hydro pressures were so high. Nobody had the nerve to answer my question on the open forum and I only got one personal message from a gent down under.

I had never considered that anyone would actually put boiling water in the tender tank. This is the same as putting the tank in the oven @ 200 deg. F. which is also a bad idea.

The Round house site also says: "If using mixed gasses, always choose the one with the largest proportion of butane." This means more butane than propane.
Cheers Dan

 

[Charles]

This topic has been covered many times in the various forums. An excellent overview was done by Kevin O'Connor:Gas fuels

An Archive file(s) available on past discussion such as this one with Chris Scott's summary about gases: Gas properties

 

[Guest]

Charles,
Thanks for the links, but I have to point out that nether thread actually specifyed the critical number of WHAT IS THE HYDRO pressure of a gas tank. This thread does give 2 answers to that question and I linked to sites that will calculate butane and propane vapor pressures. Gerald gave the link for mix curves and many thanks for that.

You might notice that I did not give an answer to the question of hydro pressure, but I gave the links for an engineer to be able to make his own desicision on the matter.

If you plan to build a gas tank a HYDRO is not OPTIONAL. I was personally in charge of the crew of a merchant ships durring Coast Gaurd inspections and have done hydros on several types of pressure vessels. This is engineering 101 and I can see that several members of this group never took the course.
Regards Dan

 

[highpressure]

HOW ABOUT CANNING METHANE GAS. After eating Carol's White Bean Chili I am a real producer & it is all going to waste.

 

[Guest]

Larry I can tell you exactly where to put the hose......

Dan

 

[Charles]

Dan
This related article might have some useful information:
Testing of boilers and gas tanks