Why you need bigger acetylene tanks (other than having to refill more often):
1/7th Rule Acetylene is disolved in liquid acetone. Its release is similar to boiling a cryogenic liquid requiring the absorption of heat to maitain the pressure equilibrium. If you exceed the draw rate the liquid cools until it will no longer evaporate. On the way it cools the container and we observe condensation and frost forming on the container surface (especially propane bottles). Thus we say it has "frozen up".
To further agrevate the problem in acetylene cylinders you have the explosion prevention pumice foam fill that prevents circulation of the acetone, thus heat absorption is very slow. In propane cylinders it is common to see frost form on them but it is rare on acetylene cylinders. Generally acetylene cylinders just quit working without warning.
For brief periods cylinders will deliver much more than the 1/7th draw rate. The 1/7th rule is such that you can continously draw gas from the cylinder until it is empty. At the draw rate you theoreticaly have 7 hours of fuel at a nominal temperature (I'd guess 70°F or 21°C). So in cold conditions the rule may be a 1/10th rule or in very hot conditions a 1/5th rule. . .
WARNING!
Acetylene is dissolved in acetone in th porous filling of the tank. It is NOT stored as a compressed gas, because if that is done it can/will explode at any pressure above 15 psig. If you draw more than the 1/7 of the cylinder size per hour, acetone from the tank is drawn out and may damage the regulator, hoses and seals. The flame will sputter. If too much acetone is removed, the tank can explode when subjected to rough handling after use. Acetylene is a dangerous material and needs to be handled with respect.
From:
http://www.anvilfire.com/FAQs/gasfacts.htm
