Hi all How to calculate this? Are there any general formulae? Besides, since a given tip has a given set of OA pressures, which is the acceptable variation range? And, there is some rule of thumb regarding how long should be the flame inner cone as per tip size?
Cutting tip manufactures have charts for the asking or download that show flow rate and pressure setings. Acetylene cylinder pressure is poor indicator of gas in cylinder. Acetylene cylinders and propane cylinders are stamped with empty weight called tare weight. 14.6 square feet of Acetylene per each pound in cylinder above tare weight. If you weigh cylinder you can calculate how much gas has been used and how much is left. That with time torch was burning lets you calculate flow rate.
Must keep Acetylene cylinder pressure above 25psi or acetone will be drawn out with gas.
I did not pay close attention to the tip chart and the flow rates were at the far right edge of the page. Dumb of me! Now, if 14.6 ft³ each @, so my 3 kg tank has 87 ft³ aprrox. therefore 1/7 of that is 12.5 ft³. .
This would mean the largest tip I can use safely is a #4. please correct me if I'm wrong
That's right, for your tank size a Victor #4 welding tip would be max. For a Harris tip it would be a #6, and for an Airco torch it would be a #5 (same flow, different tip numbering systems for different torch manufacturers). This tip size is rated for single pass welding 1/4 inch steel.
Note too that cutting tips have yet another numbering system. For your tank size you're limited to a #1 Victor cutting tip. That would also be a #1 Harris, or a #2 Airco cutting tip. This tip size is rated for cutting 3/4 inch steel.
For heating, you're limited to the smallest rosebud tip, a #5.
For larger jobs, you either have to go to a larger acetylene tank, or gang multiple acetylene tanks together with a manifold, or use an onsite acetylene generator (available with sustained flows up to about 100 cu ft an hour). Or for cutting and heating only, you can switch to propane fuel gas (with the proper propane tips and
*all fuel* rated hoses).
Reading the charts is a good exercise for those thinking of using small tanks such as a MC or B tank. A MC tank (10 cu ft) won't even properly feed a 00 tip (1/16th inch welding capacity), and really should be limited to a 000 tip (1/32 welding capacity). The B size tank (40 cu ft) can just barely feed a #2 tip, but really should be limited to a #1 (3/32 welding capacity).
The golden rule of acetylene tank safety is that no matter what size tank you have, it should take 7 hours to empty it at sustained draw. So if you're emptying a tank quicker than that, you're in dangerous territory and need to switch to a smaller tip (or a bigger tank).