1/7 Acetylene Withdrawl Rule

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I recently purchased a small Victor tote outfit mainly to heat up stubborn bolts on auto exhausts and the like. It came with some Victor 150 series light duty regulators and the 100FC medium duty handle.As you've probably already guessed it has a MC 10cf acetylene and a 20cf oxygen. It included a model W-1 size 1 welding tip that I use for heating.Now here is where my question comes in according to the 1/7 withdrawl rule this tip consumes 3 CFH at 3 PSI and 6 CFH at 5 PSI. I attached the PDF from Victor it's on page 5.It's obvious I can't run this tip for an hour but doing some math:10 cf tank / 7 = 1.42 cubic feet safe withdrawl per hour.3 CFH / 60 minutes in an hour = 0.05 cubic feet per minute.So 0.05 * 28 minutes = 1.40 cubic feetAlso at 5 PSI acetylene since the tip consumes 6 CFH I get:0.1 * 14 minutes = 1.40 cubic feetSo by this math it it safe to say I could get 28 minutes of safe run time at 3 CFH and 14 minutes safe run time at 6 CFH before I violate the 1/7 rule and start sucking acetone?I have no intention of ever running it this long since I'm only using it for occasional quick heating but I just want to make sure there aren't any flaws in my math. Or that there are some gotchas that this rule doesn't cover for smaller tanks.Thanks for the help. Attached ImagesVictor Nozzle Flow Rates.pdf (97.8 KB, 485 views)Last edited by Krankshaft; 12-20-2010 at 05:55 PM.
Reply:The withdrawal rate doesn't have a duty cycle like a machine does, where the cylinder recovers while not being used. If the gas use rate is too high, the gas carries acetylene with it, sort of like a soda frothing when the pressure is released too fast. Besides the gas carrying the acetylene into the regulator, lines and torch, it removes it from the cylinder, leaving voids. Acetylene is unstable when under pressure and when not dissolved in the acetylene, so the loss creates a dangerous condition.
Reply:You need to substitute the word acetone for acetylene except for the second to last acetylene.
Reply:I worry about that also.  However, I am not real enthused about your calculation.   I have never seen any information that says that the 1/7 rule has a specific time period associated with it.  (Electric welders are usually given a duty cycle based on a 10 minute period, so 3 minutes out of 10 is 30% duty cycle.)I would note that this situation is pretty common, that the cutting tip on most any oxy-acetylene rig, used with a small tank, will violate the 1/7 rule.   That means that violating this rule must be common.  I have not heard of people having specific problems when they violate that rule.  So my opinion is that it is a good rule, but frequently violated.I would be inclined to not worry about that for short occasional usage, which I am sure is common.  If you were going to do this often, or for more than a few minutes at a time, that might be a concern.  I recently bought a size 8 heating tip (rosebud) that uses propane, so I no longer need to think about the 1/7 rule.  With propane, the only limit is freezing the tank, which you can prevent by setting it in a pan of water.Consider buying a larger acetylene tank.   The B tanks are commonly available used for $20-$50, empty, and the dealer will swap the tank with you for the price of the gas.  This would be more important if you needed a larger tip.RichardSculptures in copper and other metalshttp://www.fergusonsculpture.comSyncrowave 200 Millermatic 211Readywelder spoolgunHypertherm 600 plasma cutterThermal Arc GMS300 Victor OA torchHomemade Blacksmith propane forge
Reply:Originally Posted by Jay OYou need to substitute the word acetone for acetylene except for the second to last acetylene.
Reply:Originally Posted by Oldiron2[B][SIZE="3"][I]:The withdrawal rate doesn't have a duty cycle like a machine does, where the cylinder recovers while not being used. If the gas use rate is too high, the gas carries acetone with it, sort of like a soda frothing when the pressure is released too fast. Besides the gas carrying the acetone into the regulator, lines and torch, it removes it from the cylinder, leaving voids.Acetylene is unstable when under pressure and when not dissolved in the acetone, so the loss creates a dangerous condition.
Reply:Something that was also pointed out to me by a sales rep, the 1/7th rule applies to the available volume in the tank. Meaning that as you draw down the acetylene (not acetone) in the tank, the 1/7th applies to what remains. So at 1/2 tank, you can now effectively draw 1/14th and so on
Reply:With the smaller cylinders and small tips there usually is not a big problem overdrawning acetylene.  An acetylene cylinder is much like a bottle of Soda, it will build a little head pressure that exceeds the 1/7 rule for a short period of time.  Most jobs with a small rig are very quick so there usually is no problem with over drawning.  One sure sign that you are over drawing acetylene (or any fuel gas for that matter) is if the flame "pop" out.  Acetylene burns at a constent rate, if there is no enough gas coing out the tip, the flame will burn back into the torch.  If you are using a big tip on a small tank and the torch "pops" off, you need to get a bigger cylinder are use a smaller tip.  Do not attempt to continue to use a torch and tip combination that "pops' off, you will damage the torch.OAdoctorwww.regulatortorchrepair.com
Reply:So what rate do you think you are at when using a rosebud on your torch?
Reply:The math on a rosebud wouldn't work it consumes more CFH than the quantity of the tank  .
Reply:Never heard of this rule? I set the gauge at 15psi on acetylene and 50 on the oxy and let her rip all day long. Never had problems?
Reply:Originally Posted by sooeey2uSo what rate do you think you are at when using a rosebud on your torch?
Reply:Originally Posted by jgbalesdentSomething that was also pointed out to me by a sales rep, the 1/7th rule applies to the available volume in the tank. Meaning that as you draw down the acetylene (not acetone) in the tank, the 1/7th applies to what remains. So at 1/2 tank, you can now effectively draw 1/14th and so on
Reply:Of course it applies to the total capacity, and not contentIf it applied to remaining content, you would never be able to finish the tank.  (Think about it, it is a good thought experiment, or just look up Zeno's Paradox).
Reply:oxygen454,With a comment like that, I suspect you SHOULDN'T BE USING AN O/A SETUP.Without an explanation such as "I'm using a manifolded Acetylene setup with a large cutting torch" etc. this is very dangerous guidance.First time you pull acetone thru your regulator and trash it, you may feel differently.Basically, just a dumb/unsafe comment.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:So if a tank is overdrawn and the acetylene can't come out of solution fast enough is it common to see the high side tank pressure drop before the tank starts spitting acetone?
Reply:If I get close to an overdraw issue, or the propane jug is closer to me than an acetylene tank, I heat and cut with propane.I got curious and asked about propane with those regulators since I never heard that question answered elsewhere:SubjectVictor Acetylene Regulator - SR160AR-200 (MC) Rear Entry - Light Duty questionAre the internal "soft parts" in these compatible with propane, propylene, etc fuel gases as are those in the larger series Victor regulators?I wouldn't expect cheaper seals in the light-duty equipment, but better to ask and be sure.I understand the pressure range is less, but I don't need to run any of my equipment at pressures beyond the recommend range of this regulator.Yes you are correct . Our fuel gas regulator are compatible with all fuels. You can use a Acetylene regulator on a LP gas cylinder but not a LP gas regulator on a Acetylene cylinder. The reason is of the delivery pressure is to high for Acetylene and this can cause a explosion. And as for the pressure setting there should never be any reason to need more pressure on a Oxy/ Fuel setup.Hope this helps.Ronnie ReynoldsHP&I  & MANIFOLD TECH800-569-0547
Reply:I'd like to bump this topic for further clarification.I just acquired a B size acetylene tank to use with a medium size Victor torch set up.  Using the 1/7 rule the maximum use rate would be just under 6 (40/7) cubic feet/hr.By reading the acetylene consumption tables from Victor (Safety and Operation Instructions Issue Date May 14, 2008 Form 0056-0138), this seems to limit me to using a number 1 or 2 welding tip for welding. The number 1 tip is rated at 3min and 6 max cfh acetylene consumption.  The number 2 tip is rated at 5 min or 10max cfh.  This seems to limit welding with a B cylinder to metal under 1/16".  Is that correct?Looking at the cutting tips, even the 000 type 3-101 tip is rated at 6 to 11 cfh by Victor.  How can that be?Even the #4 size MFA heating nozzle (?Rosebud) is rated at 6 min and 20 max cfh of acetylene consumption.What gives?  Are B size cylinders only for jeweler's torches?  Doesn't seem to fit at all with real world experience using B size tanks.
Reply:Bump. I'd also like some more clarification/expansion on this topic of discussion.I'm considering going with a 40cf acetylene cylinder & 40cf oxygen cylinder for my "hand carry" portable outfit for HVAC/plumbing purposes (a 10cf/20cf outfit just seems way too small for daily use or larger jobs).By the logical arguments on this thread thus far, my understanding is that I can't use a tip that is rated for more gas flow than 1/7 of the cylinder volume.For example, I cannot use a tip that is rated at 10-12 CFH even intermittently on an acetylene "B" cylinder (which allows ~5.7 CFH withdrawal) because it will draw out acetone.ESAB's manufacturer literature says "Withdrawal rate will increase with wind velocity and intermittent usage; reduce with lower temperature."Is that accurate?
Reply:I can't vouch for any of the recommended withdrawal rate tables or any of the arithmetic, but I have considerable experience with B and MC cylinders.  These small cylinders are OK for portable use and light duty gas welding.  You can heat a recalcitrant nut for removal here and trhere, even burn one off with a small cutting tip.  If you need portability for occasional or intermittent use they are fine.  But forget using these small tanks for any serious heating or cutting.  Lots of kits are sold at HICs (Lowes, Home Depot, Etc) with R oxy and MC Acet cylinders complete with welding tips and a cutting head. That's how I got my first set with a Harris torch.  I have used these kits for more than 30 years, but mostly for an occaisional rusted on nut or automobile brake drum rusted to the axel stub.   When I started doing some real heating and cutting I quickly realized these cylinders are far too small for this sort of work.  The flame sputters and pops and turns green when the acetone starts to contaminate the gas flow and that happens way to easy when trying to heat anything serious.  Not good.  I have turned to propane for all my heating and cutting work.  I bought a 70lb bottle, the tallest I can transport upright (as required by law) under the roofline cap on my Ford Ranger.  I can withdraw the propane as fast as it will vaporize right up until it completely runs out and there is no concern about withdrawal rates.I still have a small R/MC kit though I don't use it.  I have two B cylinders I use only with a plumber's torch which requires no Oxygen.  The little plumber's torches won't over-draw the acetlyene off the B until it runs out.I am considering selling the small R/MC kit and maybe one of the B cylinders.  They are just taking up precious space.  I will probably keep my only 60 cf Oxy and one B cylinder for portability but like I said above, I hardly ever use them today.- MondoPS:  Gawd those little cylinders are expensive to fill!  Twice the price per cuft of the much larger 145 cf cylinders!mMember, 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:We thought we might actually want to weld or cut something a hair thicker than sheet metal, so we rented a 200 CF tank.  Still isn't much when you consider a rosebud or a right proper welding tip."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 only reason I would want to use O/A is because I have somehow accumulated a bunch of R/RM hoses and regulators and tips for O/A. ... and its flame characteristics (non-oxidizing and not hydrogen-rich) can be beneficial for certain types of brazing. ... and it doesn't eat the oxygen up nearly as fast as other fuel gases.Otherwise, sure, air-propane and oxy-propane will get the job done (soldering, brazing, heating & cutting). No withdrawal rate issues, a lot more BTUs in the secondary flame, and if it's cold, just get a portable heater and keep the cylinder warm.
Reply:Keep in mind that the CGA has changed the recommendation to 1/10th too."The things that will destroy America are prosperity at any price, peace at any price, safety first instead of duty first, the love of soft living and the get rich quick theory of life." -Theodore Roosevelt
Reply:Krankshaft  -  To readers, and walterbrunswick:Apologies forward for my mis-post.OpusLast edited by OPUS FERRO; 01-11-2013 at 12:00 AM.
Reply:Oh, come on.  O/A hasn't killed that many people.  At least the folks who used it wisely can't remember those who didn't."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 welderOkay, let me get this. We have major manufacturers and the CGA telling us to go by the 1/7th rule, and then we have this guy "OPUS FERRO" on this forum telling us that it doesn't apply. Hmm, I wonder who is the wiser here.What does the amount of acetylene that acetone can absorb (I know it's about 20 times its volume) have to do with releasing the acetylene in a certain time? Time is what is important here.
Reply:KrankshaftYour algorithm is AFU, and based on a false premise, "sucking acetone?"You are good at math, and lost on equipment and procedure. Read the basics. Belching acetone can occur, but only from [a comedy of] serious procedural violations.Moderators:  Acetylene-bottle-discharge-rates: and all of acetylene's confusions, may be best addressed in a Sticky.Until then, and to all of the acetylene pundits, "acetone has the property of absorbingmany times its own volume of acetylene"  -  The Oxy-Acetylene Handbook, LINDE AIR.CO/2 in a soft drink, describes the concept, but does not address the magnitude of absorbtion that makes an acetylene bottles possible and functional. The 1/7 is much more complex than what it takes to safely operate an O/A torch.In application, the only time 1/7 is an issue is when trying to fire a Rose-Bud on a half bottle minus.  OpusLast edited by OPUS FERRO; 01-10-2013 at 11:48 PM.
Reply:OPUS FERRO, you're telling us to "read the basics." What basics? These are manufacturer's instructions.When you said "serious procedural violations" you didn't go into any specifics. What would that include? Aside from laying the acetylene cylinder in a horizontal position.I've already responded to your "property of absorbing". It is a matter of the TIME during which a certain volume of acetylene can be released from the acetone without causing the acetone to evaporate.raferguson's post made some good points; this rule is a good rule to adhere to, although it is often violated, and that is okay, as long as it's not on a constant basis.The 1/7th rule is more of a "rule of thumb" is what I'm understanding from all this.Last edited by walterbrunswick; 01-11-2013 at 01:45 AM.Reason: I was a little too hasty/snappy with my reply.
Reply:Originally Posted by oxygen454I set the gauge at 15psi on acetylene
Reply:I will go along with post 8The rule, at least the rule I choose to follow,  Is for half full tanks at room temperature.  For all the discussion and arguing about this topic a correction factor for temperature is seldom discussed and I have never to my recollection even read it.  The how full the tank is may or may not be all that much of a correction factor.  I have an acytelene cylinder that is essentially useless in the cold of winter but shows 60 pounds on a hot summer day,  At least it seems that way, I have yet to attempt to exchange it as it is a lease size one.Fran
Reply:Originally Posted by KelvinYikes. Did you notice the red line on your acetylene regulator at 15 psi?Acetylene can instantaneously explode (even without the presence of oxygen) at pressures as low as 15 psi.
Reply:Originally Posted by fran...k.I am pretty sure it was on here and quite a while ago someone went to the trouble of explaining how it was possible to have 200 psi or so in the regulator but on the output side 15 was the max.  The reasoning was if the gas was in a small enough space ie inside diameter of tube or pipe any dangerous phenomenon woldn't propogate.
Reply:(except in approved cylinder manifolds)How to get over 15 psi anyway?  Use a propane regulator or the regulator seat isn't working right and the pressure climbs once you shut down the torch or whatever device.
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Reply:You can say that again! You can say that again!But I repeat myself. But I repeat myself.Pretty good video. Pretty good video.
Reply:It should have repeated more often - most kiddos in school have about a 30 sec focused attention span Dave J.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:Originally Posted by walkerweldYou can say that again! You can say that again!But I repeat myself. But I repeat myself.Pretty good video. Pretty good video.