O/A: Fuel gas withdrawal rate vs regulator pressure

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The conventional wisdom is never withdraw acelylene from a cylinder at a rate that exceeds 1/7 the volume of the cylinder per hour (as measured in cuft).  Many sources still cite this standard.  Some sources promulgate the **NEW** wisdom is never exceed a withdrawal rate in excess of 1/10 the volume in SCFH.We also know not to use acelylene at regulated pressures above 15 PSI because C2H2 is not stable at pressures above that.     These things are nice to know and important for safety.  Right-o.  Most A/O kits have regulators and gauges that show cylinder pressure and regulated hose pressure in PSI.  Nice!  Recommended torch settings are given in PSI for various tips and tasks.  But...... How is the flow rate measured or calculated? If I have my Acet reg at 5 psi, then how can I calculate the flow rate in SCFH ?  -MondoMember, AWSLincoln ProMIG 140Lincoln AC TombstoneCraftsman Lathe 12 x 24 c1935Atlas MFC Horizontal MillCraftsman Commercial Lathe 12 x 36 c1970- - - I'll just keep on keepin' on.
Reply:An interesting question. I bought my O/A in 1977. The only thing my instructions said was Acet. max 15 lbs. I took an O/A class last year. But since they're set up with manifold gas supply, the issue never came up. I don't remember reading about it in my training manual. Until I discovered internet welding earlier this year, I'd never heard about the 1/7 or 1/10 rule.I have about 3 dozen welding books, and I've read most of all of them. My point is: even if it's a critical safety issue, few know about it. I don't have a rose bud however.9-11-2001......We Will Never ForgetRetired desk jockey. Hobby weldor with a little training. Craftsman O/A---Flat, Vert, Ovhd, Horz. Miller Syncrowave 250
Reply:My book has the Recommended Psi/consumption rate settings for each tip -Probably a chart for your brand on line some where.http://www.hoopersupply.com/tipchart.htmlLast edited by Broccoli1; 09-14-2008 at 09:33 PM.Ed Conleyhttp://www.screamingbroccoli.com/MM252MM211 (Sold)Passport Plus & Spool gunLincoln SP135 Plus- (Gone to a good home)Klutch 120v Plasma cutterSO 2020 benderBeer in the fridge
Reply:Most A/O kits have regulators and gauges that show cylinder pressure and regulated hose pressure in PSI. Nice! Recommended torch settings are given in PSI for various tips and tasks. But...... How is the flow rate measured or calculated? If I have my Acet reg at 5 psi, then how can I calculate the flow rate in SCFH?
Reply:""Get hold on an empty clear plastic windshield-washer jug.I immediatly saw where that was going.  Great idea, and it would provide some reasonable data.  It will also leave me holding a half-gallon of free acetylene gas in a plastic jug, just waiting for a spark to ignite it.  I suppose as long as I keep the neck of the jug below the surface of the water I'm in pretty good shape.  It is what happens next that might be just a little dicey.  One might have some fun with this, or one might have a disaster trying to have fun.  I am familiar with engineering this, diameter of hose, length of hose, inside surface friction, orifice opening, torch handle valve setting...  all these things come into play.   I was just wondering if there were any "rules of thumb" that might provide aproximations.  I will dig around on the torch manufacturer's web site to see if I can find some tables for my equipment.  If anyone has any general guidence please don't be shy!Harris Port-a-Torch part number 4403078Comes with:with MC and R cylindersOx reg: 601-100-540Fuel Reg: 601-15-20012' of 3/16" twin hoseH-16-2E mixerCutting attachment: 71-3Cutting tip: 6290-1ACWelding tip: 23A90-3(yeah, I know, MC/R is the most expensive way to buy these gasses.  I don't use the torch very much, 1 refill since Jan 1.)-MondoMember, AWSLincoln ProMIG 140Lincoln AC TombstoneCraftsman Lathe 12 x 24 c1935Atlas MFC Horizontal MillCraftsman Commercial Lathe 12 x 36 c1970- - - I'll just keep on keepin' on.
Reply:http://www.harrisproductsgroup.com/techdata/TipFlow.aspYour #3 welding tip is rated for welding 1/16 inch steel, and has a rated flow rate of 5-11 CFH when welding.So per the 1/7 rule (mentioned on the Harris TipFlow page as well), with a #3 tip you should use at least a 35-77 ft3 acetylene cylinder.The MC cylinder is 10 ft3.So to me it looks like the MC cylinder should really only be used with the #0 or #1 tip for welding (1-3 and 2-5 cfh flow rates respectively).btw, the Harris welding tips look like they are 'handily' sized as the tip number is the recommended pressure for all of the standard tips except the #0 (0 psi is OFF and thus there is no flow) which is recommended as 1 psi.  So your #3 tip is supposed to be set to 3 psi, oxygen and acetylene with the equal-pressure torch head.  A #5 tip would be 5 psi, a #1 tip is 1 psi, etc, etc.Acetylene is a useful but possibly dangerous fuel.  It is flammable, explosive when mixed with air/oxygen, is unstable at high(er) pressures that aren't all that high (typical 'safe' pressure for actylene is 15 psi, that usually allows a bit of a safety margin), and if too much acetylene is withdrawn from the cylinder too fast you also have the problem of the acetone in the cylinder getting 'sucked' out and of the acetylene decomposing (explosively) in the cylinder as well.Last edited by MoonRise; 09-15-2008 at 10:45 AM.Reason: more info  The best laid schemes ... Gang oft agley ...
Reply:I would think that the length of time the welding is done would have some effect on what the maximum rate would be. In Mondo's situation, if he's using his # 3 tip for a quick brazing job, that may not cause the problem that using the tip at full output while welding a 5' long seam would. I've never seen any mention of this factor anywhere. How often do you see/hear that acetylene cylinders should not lie on their side, even when not in use, because of the acetylene? How long do they need to stand upright after being on their side, before it's safe to use them?
Reply:When the cyl is too small to meet the 1/7 guideline the acetylene can't dissolve out fast enough to keep up with the torch. Low flow = backfires.I got some LOUD backfires when I tried using #8 rosebud with a 150 cu. ft. acetylene tank. After talking to my LWS guy, he explained the flow problem with small tanks/big tips and why it's a potentially dangerous mix. He recommended I either quit using a rosebud, or switch to propylene gas for heating. During our conversation I asked my LWS guy the same question you ask here (how exactly do I calculate flow?). In a moment of rare serendipity, the Victor factory sales rep. was making deliveries at the LWS that day. He overheard are conversation and said "hold on a sec while I go to my truck". He comes back a minute later and hands me a  Victor Welding and Cutting Guide (about 1/2" thick book. It's like an owners manual for all their products made within the last 20 years combined into one book). Sure 'nuff, it has all the flow charts I will ever need listed by tip size. Since all my large torches are Victor, it was the exact reference I needed. Even better - It was free.I'm sure that if you write Harris, they will send you with something similar for their line of torches. A manufacturer will almost always provide data when it directly relates to a safety issue, and Harris is probably the most accurate reference.-Matt------------------------------------------
Reply:Want the free reference book on OA welding, cutting, and heating and O/A safety that Hephaestus described in his post?  Go to http://www.thermadyne.com/victor/content/view/93/268/ and send an e-mail to the nice folks at Thermadyne asking for Manual No. 56-0114 or e-mail [email protected].  It gives low side regulator settings that will result in the required gas flows for different cutting and welding tips.  The major variables that can affect the use of their book settings are the length of your hoses and the head losses through your torch if it is not a listed Victor model. My Harbor Freight OA setup is a Victor clone, and the settings in the HF manual match the settings in the Victor book for the same tip size.TeddCoHTP Microcut 400 & Invertig 160DC  Smith Dual Guard MD-510 OA Rig  Lincoln SP135+  Hobart Stickmate LX 235/160
Reply:Thank you all for the responses, especially Hepaestus and Teddco for the Victor information!    I have been using the #3 cutting tip that comes with the kit for heating and cutting.  No problems yet.  But I will procure that book from Victor, and any offered by Harris (Div of Lincoln Elec.)-MondoMember, AWSLincoln ProMIG 140Lincoln AC TombstoneCraftsman Lathe 12 x 24 c1935Atlas MFC Horizontal MillCraftsman Commercial Lathe 12 x 36 c1970- - - I'll just keep on keepin' on.
Reply:Originally Posted by MondoThank you all for the responses, especially Hepaestus and Teddco for the Victor information!    I have been using the #3 cutting tip that comes with the kit for heating and cutting.  No problems yet.  But I will procure that book from Victor, and any offered by Harris (Div of Lincoln Elec.)-Mondo
Reply:You and me Ed-broccoli.The very first line on my earlier response had the -exact- Harris tip-chart for Mondo's Harris torch/tip.Sheesh, I might get a complex or sumpin.    The best laid schemes ... Gang oft agley ...
Reply:MoonRise, Broccoli1:I'm sorry!  You guys can have an extra biscuit too! Ok, ok, Everyone get an extra biscuit!And a V-beer too!      Member, AWSLincoln ProMIG 140Lincoln AC TombstoneCraftsman Lathe 12 x 24 c1935Atlas MFC Horizontal MillCraftsman Commercial Lathe 12 x 36 c1970- - - I'll just keep on keepin' on.
Reply:I realize this is a year-old thread, but I thought it would be useful to post that the Victor "Welding, Cutting, and Heating Guide" Manual Number 56-0114 is now available as a freebie download on the web.  All 244 pages can be gotten from Victor at:http://www.thermadyne.com/IM_Uploads...20guide_lo.pdfBecause it's in electronic form, it's easy to open a word processor doc and copy the charts and tables that are important to your own work and build up a custom poster to put by your bottles or table.  Hope this helps,Dave