Question about 1/7th rule for acetylene

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Thinking about tank sizing the other day got me wondering about this.  I am planning on renting a 140cf acetylene which should cover me with room to spare on my torch setup.  I have a prestolite w-200 torch and currently three welding tips. Size 4, 6, and 9.  The numbers refer to the flow rate.  If I remember right the largest tip is 30, so I would be beyond the 1/7th safety factor with that tip and tank size.   In my reading it seems that balancing the gases is the best way to set the regulators for specific tip sizes. (as opposed to trying to dial in a number on the regulator). This leads me to my question, if I have a tip that flows 6 and I have balanced the gases, am I flowing 3 of oxygen and 3 of acetylene?  Does that make sense?  If that is the case, wouldn't the 1/7 rule be calculated off of the acetylene half of the total flow rate?  Am I way off and a 6 cfh tip flows 6 oxygen and 6 acetylene? Thanks for the help.
Reply:villageboatshopYou have read too much, and experienced too little.The 1/7th delivery is only an issue when using a Rose-Bud on 1/2 to 1/3 of a tank or less.Flame-on, and weld to exhaustion, if your bottle size doesn't perform to expectations, simply upsize.Opus
Reply:Originally Posted by villageboatshopThinking about tank sizing the other day got me wondering about this.  I am planning on renting a 140cf acetylene which should cover me with room to spare on my torch setup.  I have a prestolite w-200 torch and currently three welding tips. Size 4, 6, and 9.  The numbers refer to the flow rate.
Reply:I am not familiar with the w-200 torch tips/numbering scheme and couldn't find a chart offhand that listed the actual flow rates.  Looked more like the numbers corresponded to the PSI on the acetylene.  I guess you could cross-reference the tip drill size to an equivalent tip by another manufacturer and approximate the CFH."USMCPOP" First-born son: KIA  Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:Try this it is the owners manual for pretty much what you have.http://naweb1.esabna.com/literature/...t_F-9773-X.pdfFor most outfits the number of the tip is the number of the cubic feet (standard) per hour of acetylene.  The alternate fuel tips are sized for the same amount of heat for each number as the acetylene one.  Harris however uses the number to denote the pressure on the regualtor at least when the number is below 15 and acetylene tips.  Actylene is quite temperature sensitive.  I believe that one sevnth rule is for half full tanks (cylinders) at room temperature and a continious draw.  A short time doesn't bother me to stretch it and in the winter with cold acetylene cylinder things don't work like room temp.  For those three tips I wouldn't have a problem working off a 40 cubic cylinder.EditThe 1/7 rule ought to be in this manual apparently it isn't in the above onehttp://naweb1.esabna.com/literature/...g_F-4644-N.pdfLast edited by fran...k.; 06-25-2013 at 05:40 PM.
Reply:Thanks for the responses.. I do remember the tip size equating to flow from the esab manual.  This specifically.."Size indicates approximate acetylene consumption in cf3/hr at normal operating pressures"The oxygen is approximately 1.1 to 1.5 parts to 1 part acetylene. So my assumption was wrong in that a size 6 is 3 and 3 of both gases.  More like 6 of acetylene and 6.6 of oxygen.  Thanks.
Reply:Originally Posted by fran...k.... For most outfits the number of the tip is the number of the cubic feet (standard) per hour of acetylene. ...
Reply:you dont need a rosebud to get in trouble. a moderatesize cutting tip uses 12 scfh  acetylene,  on a smaller tank will exceed 1/7 rule which is now the 1/10 rule..
Reply:IMO, I wouldnt worry about it too much.  I have a rosebud for my torch, cant remember the numbers but its about close to .75" diamater.  I run it off a 250cf O2 and 80cf acetylene and have never had a problem.  Been using that setup for close to 10 years.  Ive used it long enough (was trying to straighten a loader boom) to drain a fresh pair of tanks.  Switched to my other set and kept on going.  That was probably 5 or 6 years ago.  Same with my cutting tips.  Used the same tanks with my tip (again, forget the numbers) for cutting 1.5" plate.
Reply:Even a smallish welding tip will consume a lot of Acetylene.  Be safe.  Look up the numbers."USMCPOP" First-born son: KIA  Iraq 1/26/05Syncrowave 250 w/ Coolmate 3Dialarc 250, Idealarc 250SP-175 +Firepower TIG 160S (gave the TA 161 STL to the son)Lincwelder AC180C (1952)Victor & Smith O/A torchesMiller spot welder
Reply:The 1/7th withdrawal rule is not about safety really. It's about not contaminating the flame with acetone (aka acetone spitting). It may also be good to avoid acetone in the equipment but I think the materials used in valves and regulators (at least nowadays) are actually compatible with acetone and will not be damaged.Below is from the CGA, Compressed Gas Association's standard on handling acetylene, CGA G-1 - 2009:Experience has shown that for welding, cutting, and allied processes, a withdrawal rate of 1/7 of the cylinder capacity per hour is generally acceptable;To minimize the withdrawal of liquid solvent in applications that are more sensitive to solvent carry-over, acetylene should be withdrawn from the cylinder at a rate not to exceed 1/10 of the capacity of the cylinder per hour during intermittent use, and for withdrawal of the contents of the cylinder on a continuous basis, the flow rate should be no more than 1/15 of the capacity of the cylinder per hour
Reply:It becomes a safety issue if you manage to withdraw enough acetone form the cylinder that there is free space in the tank, as then you can end up with free gas at tank pressure, which is highly unstable. Acetone spitting is definitely an issue too, on my B tank (40CF), using a Harris #3 welding tip (rated for 1/16" steel), I can only weld for a few minutes before the weld starts to get contaminated by acetone spitting. The tip is rated for 5-11 CHF, depending on how you adjust the flame, so at low should be within the tank's 1/7 limits, though not within the 1/10.
Reply:Originally Posted by DeuceTrinalIt becomes a safety issue if you manage to withdraw enough acetone form the cylinder that there is free space in the tank, as then you can end up with free gas at tank pressure, which is highly unstable.
Reply:BTW, when actylene bottles are refilled they are weighed and their weight compared to what's stamped on the cylinder. Then acetone and acetylene are both refilled to get the right ratio of acetone solvent to acetylene gas for that particular cylinder.So even if someone on purpose drained both the acetylene gas as well as the acetone from a tank, it wouldn't cause an explosion when it was being refilled.
Reply:I say try it . If it dont work then upgrade. I have heard it is a safety issue but I have never heard of anybody blowing up an acetylene bottle. I cut one into  with a cutting torch to  build a sand blaster and I am still here.