Definition of 1/7th

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Hope this doesn't show up twice - tried to post once and it logged me out. When operating an acetylene tank is 1/7th an instantaneous value or an avg value over a longer period say 30 min or an hour. I have been using instantaneous to be safe but I am curious if anybody knows the textbook answer. It would also be very good to have a reference. You can stop here unless you want background. I have been practicing on 1/8th" steel plate for coupons. I started using the victor 0 welding nozzle (recommended up to 5/64") that came with my set. It can be done with patience and/or multiple passes but not very practical. So I ordered an #3 nozzle. Works much better - welds look better and when I put them on a block of iron I have and beat with hammer do much better. I like this BUT I am using a 75 scf acetylene tank (1/7 = approx 10.7 scfh) victor says the nozzle uses between 8 & 18 scfh. So I have been using a pretty small flame and cutting off the gas after each weld. Want to know if I could weld for say 15 min and then stop and let the tank catch up for 15 min without being in the red zone. My interest in welding does not include 1st hand observation of exploding acetylene tanks. Hope I am not too long winded.Don
Reply:Well to add to your dilemma the CGA recently changed it's recs on withdrawal rates. The previous 1/7th rule of thumb was for intermittent use and was in place since dirt was invented. The newer guidelines are 1/10th for intermittent and 1/15th for continuous. Both rated in cfh (hour) by the way. I'll stay out of the right or wrong aspect. I do what I do but don't hand out advice based on my own practices. I will say that one can withdraw some rather large volumes for short periods of time without drafting acetone. This allows for rose bud use for quickly heating large objects.
Reply:Your tip uses between 8 and 18 cfh of mixed gas correct?  Not just acet.I do not have a textbook reference, but the LWS said a #75 rosebud was as big as I can go with a 75cf acet tank.David  Real world weldin.  When I grow up I want to be a tig weldor.
Reply:Sandy Thanks sounds like the 1/7th is flow at one time not average ... but also sounds like I can do short time amounts with minimum danger. I hate pushing the edge on safety though guess I will pony up an try an #2. Wish I had looked at that before I ordered. If it does not work as  will trade for a bigger bottle when I get working hard my LWS I rent my tanks from charges the same for rental on any size bottle - of course cost more to fill it. Probably should try the smaller tip anyway to save gas if it will work well. David Thanks - the Victor welding, cutting and heating quide shows the 8 to 18 to be for acetylene not mixed. Just out of curiosity I looked but did not see a tip designated as #75 - By thier sizing system it would be a big one - an #4 MFA tip shows to use from 6 to 20 scfh & a #15 uses from 90 to 220 scfh. your experience with the rosebud seems to agree with Sandy though that you can use a little on the high side for short periods of time.Thanks againDonLast edited by InTheSticks; 02-25-2008 at 06:30 AM.
Reply:Yes it costs more, but the price per cubic foot is lower. Not sure on acetylene as my small bottle is just a backup and doesn't get used very often, but it costs me 2 bucks more to refill my 240 O2 bottle than it does to fill my 140. Not saying if it's right or wrong, but have worked in shops where we frequently emptied the big acetylene bottles in 4 hours. You can actually do that with a scarfing tip. Usually go through 2 240cf O2 bottles to one Acetylene bottle.The difference between art and craft is the quality of the workmanship. I am an artist.
Reply:Jolly Roger,If you were emptying your acetylene tanks in four hours, you were creating a dangerous situation.  My recommendation would have been to use larger bottles, a manifold system, or consider using a different gas (propane).Just because you "GOT AWAY WITH IT", doesn't make it right.For a poster who professes to know as much as you do about welding, you sure post up a bunch of BS.Syncro 250 DX Dynasty 200 DXMM 251 w/30A SG XMT 304 w/714 Feeder & Optima PulserHH187Dialarc 250 AC/DCHypertherm PM 1250Smith, Harris, Victor O/ASmith and Thermco Gas MixersAccess to a full fab shop with CNC Plasma, Water Jet, etc.
Reply:Another reason why I use propane, except for small brazing and gas welding jobs.It is just so much safer of a fuel gas.Joewww.CummingsHauling.com