O/A: why shut off acetylene first?

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It's typically recommended that when finishing with the use of an O/A torch, you shut off the acetylene first, then sut off the oxygen.  I realize that this extinguishes the flame immediately, because the fuel gas is gone.  But in my experience it also often causes a pop (a big pop with larger tips).  But if you shut off the oxygen first, your'e simply left with the loose acetylene flame of the type you have when you spark-light the torch at the beginning of the session.  Then you can quickly shut this off.  No pop.  As long as you're careful where you're holding/pointing the tip, it does not seem unsafe.If the session has gone nicely and you're in control of the torch and flame, why is shutting off in this order (oxygen first, then acetylene) a problem? - or why is this recommended against?  Has anyone here actually experienced a problem (your own problem, or somebody else's in a shop you were working in)?
Reply:If the acetylene is allowed to continue to burn,  it can burn back into the torch body melting orings and valves.  The oxygen quickly uses up spare acetylene.  The loud pop is a quick backfire.Esab Migmaster 250Lincoln SA 200Lincoln Ranger 8Smith Oxy Fuel setupEverlast PowerPlasma 80Everlast Power iMIG 160Everlast Power iMIG 205 Everlast Power iMIG 140EEverlast PowerARC 300Everlast PowerARC 140STEverlast PowerTIG 255EXT
Reply:Who recommends that?I thought it was the other way around.Lincoln PowerMig 180cVictor O/ABandaids and aspirinI don't know what I don't know!?
Reply:It is the other way around.  Straight from the victor manual:Follow these procedures when you finish your cutting, heating, or welding operations1) FIRST, shut off the oxygen control valve, THEN shut off the fuel control valve.  A "pop" may occur if you reverse this procedure.  The "pop" throws carbon soot back into the torch.  The soot may partially plug the gas passages.2) Close both cylinder valvesand so on and so on to bleed off pressure, etc.Dynasty200DX w/coolmate1MM210MM VintageESAB miniarc161ltsLincoln AC225Victor O/A, Smith AW1ACutmaster 81IR 2475N7.5FPRage3Jancy USA1019" SBAEAD-200LE
Reply:There is a few things to keep in mind.  I don't know the exact speed but believe the number for speed of flame front for acetylene approaches the speed of sound.  It is fast!  Acetylene will burn in mixtures ranging from around 2 percent to 98 percent so it is easily ignited.   When you turn off the acetylene the remaining oxygen in the will supply the trace amounts of acetylene with oxidizer until all the fuel is used up.  If you shut off the oxy the acetylene flame will travel along the supply route to the closed oxygen valve.  Gee I hope it is closed and not leaking.........     General rule is fuel on first and fuel off first.  The only exception is if you have a burnback into the torch handle or mixing chamber.  You will see no flame but hear a high pitched scream.  The next thing that can happen is the torch will glow red in the critical area or you get a flashback all the way to the gauges.  The solution to a burnback is to quickly turn off the oxy and hopefully the acetylene will run out of oxidizer and reappear at the torch tip and then you can close the fuel valve off.  Anti-flashback valves are required in almost all jurisdictions now for good reason.   A torch that has experienced a burnback really should be sent in for cleaning, inspection and safety check.... by someone who knows what he/she is doing.
Reply:Originally Posted by AndyAIt is the other way around.  Straight from the victor manual:Follow these procedures when you finish your cutting, heating, or welding operations1) FIRST, shut off the oxygen control valve, THEN shut off the fuel control valve.  A "pop" may occur if you reverse this procedure.  The "pop" throws carbon soot back into the torch.  The soot may partially plug the gas passages.2) Close both cylinder valvesand so on and so on to bleed off pressure, etc.
Reply:Fuel on first, off first. Most texts from the 19teens on list this method to PREVENT carbon build up in the mixer etc. In fact even durring lighting the torch they would instruct users to always have a bit of oxygen to prevent a "sooty" acetylene flame as this also causes carbon build up. Present day instructions seem to have gone away from this, especially Victor. However from first hand testing, using the older method DOES reduce the carbon build up in the torch. Start thinking about it, and the older method makes a lot more sense from a safety standpoint as well.
Reply:The burning rate of the O2/Acet. mix depends on the gas ratio and is faster for higher O2 percentage. If you shut of fuel first, the mix O2 level will change upward within the torch, allowing the flame to suddenly burn back into the torch, causing the small 'pop'. If you turn of O2 first, the burning rate quickly lowers 'till only fuel is exiting the tip, so you get only a smoky flame.The safe and correct method is to shut off the Oxygen first.They can be lowered in steps to reduce smoking, but still in this order, not going to an oxidizing flame at any time..
Reply:Use of a torch and procedures to turn on and turn off the torch is one of the first things you learn in beginning welding class.Extremely important!!!Bleeding your hoses also at the end of the day.Misuse of the torch has caused many deaths and injuries.I personally know of three incidents in my area that caused death or injury.One incident in Louisiana caused 18 deaths,blew the windows out of houses for 3 mile, and blew up a LPG tanker ship. All caused by one person that did not take care of their torches.Not bleeding hoses cost a guy in my town a jaw injury and partial loss of vision in one eye.Please be responsible.  TAKE A CLASS or READ A BOOK.AWS certified welding inspectorAWS certified welder
Reply:Originally Posted by Donald Branscom TAKE A CLASS or READ A BOOK.
Reply:Originally Posted by makoman1860Most texts from the 19teens on list this method to PREVENT carbon build up in the mixer etc. In fact even durring lighting the torch they would instruct users to always have a bit of oxygen to prevent a "sooty" acetylene flame as this also causes carbon build up. Present day instructions seem to have gone away from this, especially Victor. However from first hand testing, using the older method DOES reduce the carbon build up in the torch.
Reply:If you have soot up inside the torch handle and mixing chamber it is time for a certified gas tech to clean, inspect, and repair.  You do not want the liability even in Canada where lawyers are not completely free range.  Add that to Worksafe BC on your butt and it is not worth it.    I am collecting info on fuel on fuel off first to be presented later.
Reply:from what ive seen victor recommends shutting down the oxygen first   but smith recommends the opposite.Last edited by jwright; 04-02-2009 at 09:24 PM.Reason: typo
Reply:Originally Posted by AndyAIt is the other way around.  Straight from the victor manual:Follow these procedures when you finish your cutting, heating, or welding operations1) FIRST, shut off the oxygen control valve, THEN shut off the fuel control valve.  A "pop" may occur if you reverse this procedure.  The "pop" throws carbon soot back into the torch.  The soot may partially plug the gas passages.2) Close both cylinder valvesand so on and so on to bleed off pressure, etc.
Reply:Elvergon is correct.  That is indeed what is in the Victor literature.  My Linde torch and Canox torch manuals say fuel off first.  Modern welding (1988) also says fuel off first.At this point I guess we just have to follow specific manufacturers instructions.  Anyone know a victor tech rep we can ask?
Reply:Welding Principles and Applications 6th ed says turn off gas first to blow flame out and away from tip, unless loud pops are observed everytime, then turn off oxygen first.   Then be sure flame is out before putting down torch.I guess it depends.Esab Migmaster 250Lincoln SA 200Lincoln Ranger 8Smith Oxy Fuel setupEverlast PowerPlasma 80Everlast Power iMIG 160Everlast Power iMIG 205 Everlast Power iMIG 140EEverlast PowerARC 300Everlast PowerARC 140STEverlast PowerTIG 255EXT
Reply:If anyone contacts a representative of any company which recommends the 'fuel off first' procedure, please ask for, and then report here, the reasoning behind it. Can anyone offer a reason why the explanation I gave is wrong?Seems to me that:Welding Principles and Applications 6th ed says turn off gas first to blow flame out and away from tip, unless loud pops are observed everytime, then turn off oxygen first
Reply:I'll add one to the fuel 1st list. (US gubmint, 1993)TC 9-237OPERATOR'S CIRCULARWELDING THEORY AND APPLICATIONn. Treat regulators with respect. Do not turn valve handle using force.o. Always use the following sequence and technique for lighting a torch:(1) Open acetylene cylinder valve.(2) Open acetylene torch valve 1/4 turn.(3) Screw in acetylene regulator adjusting valve handle to working pressure.(4) Turn off the acetylene torch valve (this will purge the acetylene line).(5) Slowly open oxygen cylinder valve all the way.(6) Open oxygen torch valve 1/4 turn.(7) Screw in oxygen regulator screw to working pressure.(8) Turn off oxygen torch valve (this will purge the oxygen line).(9) Open acetylene torch valve 1/4 turn and light with lighter.NOTEUse only friction type lighter or specially provided lighting device.(10) Open oxygen torch valve 1/4 turn.(11) Adjust to neutral flame.p. Always use the following sequence and technique for shutting off a torch:(1) Close acetylene torch valve first, then the oxygen valve.(2) Close acetylene cylinder valve, then oxygen cylinder valve.(3) Open torch acetylene and oxygen valves to release pressure in the regulatorand hose.(4) Back off regulator adjusting valve handle until no spring tension is left.(5) Close torch valves.http://www.govmedia.com/
Reply:WEIRD!!!!!!!!!!Maybe it's the torch brand.  I use Harris.  Light the acetylene w/o 02, give it 02 and adjust to neutral.When you shut it off, turn the Acetylene off first, then the 02.  Do it in reverse, like y'all are talkin' about..........it POPS.Been using the same torch for 12 years, and if there's carbon in it, I wouldn't know.  Still works fine.They use a Victor at the LWS, and light it with both gasses on.  Crazy thing puts out a drastic flame imediately.  I don't like that.  Could burn the daylights out of the hand holding the striker.  I really never watch the guy turning it off, but it pops every time.  I'm pretty sure he's turning the O2 off first.And BTW..... how can you get carbon in the mixer when the flame's burnin' outside the tip.  It ain' t burnin' inside the torch handle.  I'm no expert, but it seems that if it pops, there's combustion inside the torch body.  So turn the 02 off last so it doesn't pop.I dunno, maybe I just gotta weird torch.  Wouldn't surprise me"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by Oldiron2If anyone contacts a representative of any company which recommends the 'fuel off first' procedure, please ask for, and then report here, the reasoning behind it. Can anyone offer a reason why the explanation I gave is wrong?Seems to me that:is saying 'do it wrong if you feel like, unless it causes problems, and then do it right'.If there is some rare occurrence with either method, I'd like to understand it. Anyone have good access to the technical people at Linde or ???
Reply:Originally Posted by farmersammWEIRD!!!!!!!!!!Maybe it's the torch brand.  I use Harris.  Light the acetylene w/o 02, give it 02 and adjust to neutral.When you shut it off, turn the Acetylene off first, then the 02.  Do it in reverse, like y'all are talkin' about..........it POPS.Been using the same torch for 12 years, and if there's carbon in it, I wouldn't know.  Still works fine.They use a Victor at the LWS, and light it with both gasses on.  Crazy thing puts out a drastic flame imediately.  I don't like that.  Could burn the daylights out of the hand holding the striker.  I really never watch the guy turning it off, but it pops every time.  I'm pretty sure he's turning the O2 off first.And BTW..... how can you get carbon in the mixer when the flame's burnin' outside the tip.  It ain' t burnin' inside the torch handle.  I'm no expert, but it seems that if it pops, there's combustion inside the torch body.  So turn the 02 off last so it doesn't pop.I dunno, maybe I just gotta weird torch.  Wouldn't surprise me
Reply:I've got a really weird torch.  It was marketed by Sears, but it's made by Harris.Never seen a torch like it.  The 02 mix knob is under the lever between the lever and the body.  The lever depresses a little ball in the middle of the knob to supply the cutting oxygen.  I'll post a pic tomorrow.  Too lazy to unlock the shop and get it out right now"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Fuel gas ON first,  OFF first.  Been doing that for 45 years now.  Was taught that, and I taught that.  I have a Dockson torch that's over 40 years old.  NEVER had problems with carbon internally.  Did have to change an "O" ring on the cutting head about 20 years ago.  Motorcycle battery filler cap O ring worked great.
Reply:Okay.  Well, if I go with the predominant recommendation (acetylene off first, then oxygen), I'll get lots of pops.  I know this from experience with my torch.That leads me to another question. I've got flame arrestors between my hoses and my torch handle.  I bought the torch with the arrestors on it, secondhand from a friend who has since moved away - but I know the torch had quite a few years of use.  No problems ever with the torch handle, since I've owned it.  But do flame arrestors ever need to be replaced, to make sure they will function correctly when actually needed - and, if so, how often should they be replaced?
Reply:I'm with the fuel first crowd, a Smith rep gave me the reasoning.  Turning off the fuel first allows the oxygen to purge the torch of combustables.  If you turn off the o2 first, you'll have a combustible mix of fuel/air in the torch which can cause a flash back the next time it is lit.Flame arrestors only need to be replaced if they plug up.a Smith rep gave me the reasoning. Turning off the fuel first allows the oxygen to purge the torch of combustables. If you turn off the o2 first, you'll have a combustible mix of fuel/air in the torch which can cause a flash back the next time it is lit.
Reply:and if it pops when you turn it off, who cares???You just closed the valve that supplied the gas. Scared of a little noise?...Go hide in the house
Reply:Originally Posted by Oldiron2I guess the real question this brings up is, can doing it either way ever cause real problems?
Reply:Emailed Victor on April 5, 2009 and they sent me this:VICTOR  A THERMADYNE CompanySeptember 29, 2003Re: Shutdown Procedure for Oxy/fuel Cutting TorchesTo Whom It May Concern:Victor Equipment Company recommends a shutdown procedure for oxy/fuel torches that isdifferent to that recommended by most other manufacturers of gas welding and cuttingapparatus. There are times when this difference in procedure may cause confusion andconcern. From this, the following is an explanation behind the logic of our procedure.Victor recommends turning off the oxygen first, then the fuel when shutting down an oxy/fueltorch. The primary reason for this procedural sequence is SAFETY. This can best beexplained with the following three reasons:1. One of the most common causes of backfire and sustained backfire (burning insidethe torch) is overheating of the tip or nozzle. The primary cause of overheating isinsufficient flow (velocity) of gases which allows the >5000° F flame to burn on thesurface of the tip or even slightly inside the preheat orifice(s). Proper gas flow withsufficient velocity causes the flame to burn slightly away from the tip end.One of the simplest ways of determining adequate fuel flow when using acetylene isto have a “soot free” flame when the fuel is on and no oxygen is flowing. Thus, if theoperator turns off the oxygen first, and the flame produces soot, he is reminded thatinsufficient flow was used. From this, the operator should either increase the flow orchange to a smaller size tip. (This depends on the application.)2. All valves have the potential of leaking at one time or another. When the fuel isturned off first, the flame is immediately extinguished, even though there might be asmall fuel gas leak. If the oxygen valve is closed first, the flame will continue to burn(hopefully without soot!). Then, when the fuel valve is closed, and if a leak is present,a small flame will continue to burn. This will immediately warn the operator of aproblem.Neither shutdown procedure will show an oxygen leak, but at least in the lattermethod, the operator can detect the more hazardous of the two.3. As mentioned, other manufacturers recommend closing the fuel first, and then theoxygen EXCEPT when there is a sustained backfire (burning inside the torch). Inthis case, they recommend immediately closing the oxygen valve first.Humans are creatures of habit. To recommend reversing the shutdown procedure inan emergency situation would be like telling an automobile driver to use his rightfoot on the brake for normal stops, but in the event of an accident, use the left foot. Afew seconds can mark the difference between a safe shutdown and a damagedtorch, and most importantly, possible injury to the operator.There have been claims that using our method causes soot build-up inside the torch.Victor has performed many tests and found that the soot build-up that others claim to occur is caused by improper gas flow and pressure settings, not the sequence of closing the valves. This holds true for all equipment that we have tested.It should also be noted that all industry standards organizations, such as ANSI, AWS,CGA, and NFPA, recommend the operator follow the manufacturer’s instructions for proper operation of the equipment. To this extent, there’s not a “golden rule” in the industry. Since there are basically two different ways of shutting down an oxy/fuel torch, we feel our method provides the safest way.Sincerely,David PryorManager, Product Technology and Advancement
Reply:Interesting reasoning by Victor. Thanks for posting that. I have always shut of my fuel first on my Henrob, because that is what the manual says to do, and because I have read on several forums from guys who rebuild their own torches that they believe turning off the oxygen first leads to carbon buildup in the torch. I think that is also what my old Linde, "Oxy-Acetylene Handbook" recommends, although they say different types of  torches and manufacturers recommend things and that you should probably follow their recommendations.. I remember thinking "Oh Great, how will I remember that in an emergency?" when I first read that during a flashback you are supposed to turn off the oxygen first, and Lincoln is right, I am a creature of habit.  I don't have a manual for my Smith AW1, so I have no idea what they recommend. Victor says they tested the carbon buildup theory and didn't find it to be true on the torches they tested. I wish I knew which ones they tested. I never enjoy the pop I get on a big tip when turning off the fuel first, although some say some manufacturers built that in to clean the torch. Very important and very confusing topic.Last edited by smyrna5; 04-06-2009 at 11:37 AM.Lincoln 175HD Miller AC/DC ThunderboltSmith AW1, Dillion (Henrob) Mark III, & Smith LittleTorch
Reply:Well,I guess that is good reasoning for their torches.  Remember, Victor is also now Chinese made.  I guess they have a reasoning for that as well.Esab Migmaster 250Lincoln SA 200Lincoln Ranger 8Smith Oxy Fuel setupEverlast PowerPlasma 80Everlast Power iMIG 160Everlast Power iMIG 205 Everlast Power iMIG 140EEverlast PowerARC 300Everlast PowerARC 140STEverlast PowerTIG 255EXT
Reply:From the Smith website's user manual:  http://enet.smithequipment.com/public/docs/BDBinDoc.asp?ID={D890FABD-36BC-4D97-B571-ECD520976AC9}&DownLoad=0Follow these steps for lighting and adjusting oxy-acetylene welding tips.  Having followed the instructions contained in this manual per¬taining to set up and purging, the torch may be ignited.1. Purge the hoses.2. Open the fuel valve 1/8 of a turn and ignite the acetylene using an approved friction spark lighter.3.  Increase the acetylene gas flow until the flame is no longer producing (soot) smoke.4. Open the oxygen valve until you achieve a neutral flame.Extinguishing the Torch Flame. 1. Turn the torch oxygen gas valve to the closed position (clockwise).2. Turn the torch fuel gas valve to the closed position (clockwise).Victor's and HF manual give the same sequence.  Don't you think the corporate lawyers would make sure the manual limits their liability by containing the correct information?TeddCoHTP Microcut 400 & Invertig 160DC  Smith Dual Guard MD-510 OA Rig  Lincoln SP135+  Hobart Stickmate LX 235/160
Reply:Originally Posted by rcspottEmailed Victor on April 5, 2009 and they sent me this:VICTOR  A THERMADYNE CompanySeptember 29, 2003Re: Shutdown Procedure for Oxy/fuel Cutting TorchesTo Whom It May Concern:Victor Equipment Company recommends a shutdown procedure for oxy/fuel torches that isdifferent to that recommended by most other manufacturers of gas welding and cuttingapparatus. There are times when this difference in procedure may cause confusion andconcern. From this, the following is an explanation behind the logic of our procedure.Victor recommends turning off the oxygen first, then the fuel when shutting down an oxy/fueltorch. The primary reason for this procedural sequence is SAFETY. This can best beexplained with the following three reasons:1. One of the most common causes of backfire and sustained backfire (burning insidethe torch) is overheating of the tip or nozzle. The primary cause of overheating isinsufficient flow (velocity) of gases which allows the >5000° F flame to burn on thesurface of the tip or even slightly inside the preheat orifice(s). Proper gas flow withsufficient velocity causes the flame to burn slightly away from the tip end.One of the simplest ways of determining adequate fuel flow when using acetylene isto have a “soot free” flame when the fuel is on and no oxygen is flowing. Thus, if theoperator turns off the oxygen first, and the flame produces soot, he is reminded thatinsufficient flow was used. From this, the operator should either increase the flow orchange to a smaller size tip. (This depends on the application.)2. All valves have the potential of leaking at one time or another. When the fuel isturned off first, the flame is immediately extinguished, even though there might be asmall fuel gas leak. If the oxygen valve is closed first, the flame will continue to burn(hopefully without soot!). Then, when the fuel valve is closed, and if a leak is present,a small flame will continue to burn. This will immediately warn the operator of aproblem.Neither shutdown procedure will show an oxygen leak, but at least in the lattermethod, the operator can detect the more hazardous of the two.3. As mentioned, other manufacturers recommend closing the fuel first, and then theoxygen EXCEPT when there is a sustained backfire (burning inside the torch). Inthis case, they recommend immediately closing the oxygen valve first.Humans are creatures of habit. To recommend reversing the shutdown procedure inan emergency situation would be like telling an automobile driver to use his rightfoot on the brake for normal stops, but in the event of an accident, use the left foot. Afew seconds can mark the difference between a safe shutdown and a damagedtorch, and most importantly, possible injury to the operator.There have been claims that using our method causes soot build-up inside the torch.Victor has performed many tests and found that the soot build-up that others claim to occur is caused by improper gas flow and pressure settings, not the sequence of closing the valves. This holds true for all equipment that we have tested.It should also be noted that all industry standards organizations, such as ANSI, AWS,CGA, and NFPA, recommend the operator follow the manufacturer’s instructions for proper operation of the equipment. To this extent, there’s not a “golden rule” in the industry. Since there are basically two different ways of shutting down an oxy/fuel torch, we feel our method provides the safest way.Sincerely,David PryorManager, Product Technology and Advancement
Reply:...... Attached Images"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Maybe I'm doin' it wrong, but I always light it, then adjust the Acetylene upwards to obtain a soot free flame, then I turn the oxygen on and adjust it to a neutral flame.
Reply:Gotcha.I gotta quit ramblin'Somethin' about your alligator mouth overloadin' yer mosquitoe butt"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Leastways, that's the way it was put to me last time I almost got my skinny butt kicked"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Samm,Stop making excuses; we all know you're just trying to get your post count ten times higher than anyone else's!
Reply:Hey, do ya get to be CEO after 5000?????"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by farmersammOk, this is a stretch, and I ain't the brightes bulb on the planet...........When on God's Green Earth do you light a torch where there ain't a bit of soot as you ramp up the Acetylene????????I suppose you could light it with the Acetylene full on, and singe your whiskers in the processMaybe I'm doin' it wrong, but I always light it, then adjust the Acetylene upwards to obtain a soot free flame, then I turn the oxygen on and adjust it to a neutral flame.Had a girlfriend once that used to say that "she was too pooped to pop".  Meant it was gonna be a very quiet evening
Reply:Originally Posted by paweldorSamm, I learned this from a Pipeline Weldor many years ago.  He opens his A valve then "cracks" his O valve.  Lights the torch.  NO squiggleys.  Does make a nice popping sound in the striker though.Works every time.
Reply:I found this section from a 1920 book, that may explain why there is so much confusion on shutting down. In the case of an injector type blowpipe (torch), first close the acetylene needle valve and then the oxygen needle valve. In the case of pressure blowpipes, first close the oxygen needle valve, and then the acetylene needle valve. I am not sure why the difference, but the oldtimers probably had a good reason. Since all my torches are injector types, I think I will stick with the acetylene first method that the manufacturer recommends.http://books.google.com/books?id=upx...ient=firefox-aLincoln 175HD Miller AC/DC ThunderboltSmith AW1, Dillion (Henrob) Mark III, & Smith LittleTorch
Reply:I have a completely different reason, the my dad told me... maybe 40 years ago when I started helping him in the shop (he was a certified welder and had a shop in the back yard as well)---  He told me to always shut of the oxy first.  He said that Acetylene becomes unstable, and should never be stored, above 15psig (30 psia).  Shutting off the Acetylene first could possibly trap the Acetylene in the Acetylene hose at above that level, under the right conditions (maybe a partially clogged tip???).I don't know for sure if that's even factual... but dad was ALWAYS right
Reply:I have a completely different reason, the my dad told me... maybe 40 years ago when I started helping him in the shop (he was a certified welder and had a shop in the back yard as well)--- He told me to always shut of the oxy first. He said that Acetylene becomes unstable, and should never be stored, above 15psig (30 psia). Shutting off the Acetylene first could possibly trap the Acetylene in the Acetylene hose at above that level, under the right conditions (maybe a partially clogged tip???).
Reply:Hi guys.  I'm getting back into O/A after several decades off (just for hobby) and have been trying to bone up by reading your threads.  It appears there's quite a difference of opinion on several things.  My question is regarding use of flashback arrestors at both ends of the hose.  Is this really going to affect the flow enough for me to worry about at 3-5 PSI?