Acetylene: how low can i go.

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I have been practicing quite a bit of OA welding and am running out of acetylene.  I noticed that it was getting lower.  I remember reading somewhere that I shouldn't run the acetylene all the way to empty, did I remember wrong?  how low is safe? its about 2 foot tall:
Reply:If you are using small tips and not drawing the gas very fast, you can go down to low values before the tank can't feed your flame properly. When your flame starts being an oxidizing one, and cranking up the regulator a little doesn't help for long, it's probably time to change. Tank pressure might be a few psi up to 5 or more, depending on tip size.Two styles of torches exist; Equal pressure, where the  pressures for both fuel and oxygen are about equal, and Injector, where a venturi within the torch draws the fuel gas in, so it's pressure can be much lower. The second variety does much better at using all the acetylene in the tank, but is not as common as the other type.I am not aware of any safety concerns, so long as the acetone isn't being spit up or oxygen isn't feeding back into the fuel hose or beyond. The tank needs to be closed when disconnected, and needs to have a slight (at least) positive pressure to keep any air from entering.
Reply:Keep your torches balanced and this may help abit with acetylene use,especially if their is a small leak and you don't always shut them off at the tank.Posted before your picture loaded, might consider shorter lines, for less line loss when bleeding and perhaps larger tanks.
Reply:Oxymoron-  very funny......That photo of the tanks has me worried. that oxygen guage looks very very old.The guages should not be pointed straight up because if the handle blows out  from a sticking guage it could hit you in the face. I  would put it on an angle so that you can read it but the handle is not pointing up.You may never know how low you can go on the actyelene. Know what I mean?If you get really low and your hear a rapid popping ...look out!  shut that torch off!!!Don't take chances. You could take out your neighbors houses too.AWS certified welding inspectorAWS certified welder
Reply:You need to leave a certain amount of pressure in each tank to prevent any moisture from being drawn in with outside air, due to improper seals or minor leaks if a tank is drawn completely empty. The internal pressure of at least a small amount of tank gas prevents outside air from being drawn in. This is one aspect I was taught.City of L.A. Structural; Manual & Semi-Automatic;"Surely there is a mine for silver, and a place where gold is refined. Iron is taken from the earth, and copper is smelted from ore."Job 28:1,2Lincoln, Miller, Victor & ISV BibleDanny
Reply:Originally Posted by pistolnoonKeep your torches balanced and this may help abit with acetylene use,especially if their is a small leak and you don't always shut them off at the tank.Posted before your picture loaded, might consider shorter lines, for less line loss when bleeding and perhaps larger tanks.
Reply:I think you should perhaps step back reveiw some of the basics of oxy-acetylene welding, you may want to check the "Miller" web site, I think they have some good articles.Acetylene is mixed with acetone - a solvent, which keeps it stable under pressure.Get above 17 psi+ and acetylene spontaneously combusts in the atmosphere, torch handle etc.so balance your torch to avoid this problem.Part of the problem with wanting to go low is you may get a backfire in your torch because it begins to burn in the handle, and can find it way back to the tank and you get a bad situation.I never looked carefully enough but you should get backfire arrestors on your torches and/or checkvalves.The fuel isn't the worst part of your equation the oxygen is because it oxidizes anything that burns.How do you ballance your torch, quickly -turn your acetylene tank regulator valve on to where you get carbon whisps flying around, whatever the tip may be, then keep going until they disappear keeping the knob on the torch wide open and adjust pressure with your acetylene valve, then turn your oxygen on wide open on the torch and gradually add oxygen using the regulator valve. In this manner if you do have a leak, your not losing all your gas at once, and some say it consumes fuel in the end.Their may be better descriptions so check other posts.
Reply:As soon as you notice that you need to increase your pressure at your normal settings then it is time to replace your acetylene.  Your hoses look fine to me. you can run 15Mtrs of 5mm ID hose just fine. The first thing I would do is put a set of Flashback Arrestors on your rig. You can check your system easily by pressurizing the set and then turn off the valves at the tanks and watch for a pressure drop at the contents gauges, if it drops then you have a leak somewhere.When pressurized and your outlet pressure gauge starts to rise "creeps" then you have a problem with the seat. Have a look in the spigot to see if there is a sintered filter in both regulators, especially the older one, they should be there, and they can become clogged and reduce the regulator flow rate.Cheers
Reply:i dont think you should run  with the acetylene valve wide open. tank valve only 3/4 turn open and torch valveonly open enough  so that the carbon is gone/minimized and the flame stays on the tip when you light it...then  ox with  the tank and torch valves  wide open and control with the ox knob nearer the tip to get the flame adjusted to neutral.
Reply:Yes find a method, and balance your torches,I remember they used to teach on some tanks to crack them open wide open because some have valves that seat at the top so you don't leak when open, and with the older tanks I think it was 3/4 of a turn, myself I just recently began to crack them open enough to get the right pressure to the gauges - the logic now being if you have to shut them off fast you don't want to sit their cranking the knob back for half a minute.So like thirty years after I first started welding I'm still learning.
Reply:Should open the tank valve most of the way,as you get lower contents pressure you may start to starve the regulator of pressure causing an unwanted problem, you would be reducing the flow of gas which is not a good idea, so open all the way if you want but not 3/4 of a turn!If you open a water tap what is the effect of opening it a little or a lot???CheersBilly
Reply:Acetylene tank valve  3/4 turn so you can shut it if bad stuff happens. ox tank valve wide open or it will leak..
Reply:Originally Posted by weldbeadAcetylene tank valve  3/4 turn so you can shut it if bad stuff happens. ox tank valve wide open or it will leak..
Reply:Posted by Billy:Are you serious?
Reply:Originally Posted by Oldiron2Yes he is. As stated above, the acetylene tank valve should only be opened a small amount, less than a full turn, so it can be quickly turned off if needed. It is not a high-pressure tank so the valve packing should suffice to stop leaks.The other tanks, those holding oxygen, or with other processes,  argon, helium etc., all are high pressure and the valves are made with seats at the bottom and the top; by 'back-seating' the valve, it insures no leak will occur.Modern valves are better than long ago, with both better designs, machining and materials, so might not always need this, but it's still good insurance under most conditions.
Reply:Posted by Billy:Both valves should be wide open, have to keep the flow upFlashbacks arent fussy which cylinder that they burn in, have seen both happen,If a flashback occurs better off getting out than worry about a valve
Reply:"The acetylene cylinder can only safely supply a certain volume of gas without other problems occurring, and the valve doesn't need to be open very far to do this. Shutting off the valve in the event of a small problem can keep it from becoming a larger one, and flashbacks aren't the only possible problem."The only reason that some people say not to open more than 3/4 turn is that if they get flashback they will need to close the valve quickly, back in the old daysBut these days there is no need to do that, if you have flashback arrestors connected to your equipment there is not a problem, 0, zilch, nothingThe cylinder does not control the amount of gas required, it is the REGULATOR, as long as you dont draw off more than 1/7 of the cylinder contents per hour.If you restrict the flow of gas that can cause huge problems!Anyway how about we agree to disagree?And let people make there own minds upFlashback Arrestors are the only way to go to make all the equipment safe!!!!CheersBilly
Reply:The cylinder does not control the amount of gas required, it is the REGULATOR, as long as you dont draw off more than 1/7 of the cylinder contents per hour.
Reply:A lot of things can happen between the flash backs and the tanks. A hot drop across the hoses is one of them. A guy should always watch but people aren't perfect, accidents happen. Flash backs were developed for a specific purpose.
Reply:Originally Posted by SandyA lot of things can happen between the flash backs and the tanks. A hot drop across the hoses is one of them. A guy should always watch but people aren't perfect, accidents happen. Flash backs were developed for a specific purpose.
Reply:Sometimes after I wheel the cart out of the shed, and fire up the torch, I notice some spitting and popping.  Is this the acetone?  I don't wait forever to use the cutting rig, I use it as soon as it's in place sometimes."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by farmersammSometimes after I wheel the cart out of the shed, and fire up the torch, I notice some spitting and popping.  Is this the acetone?  I don't wait forever to use the cutting rig, I use it as soon as it's in place sometimes.
Reply:as oldiron2 states, since 3/4 turn on the acetylene tank valve provides more than enough volume of gas, its no advaNtage to more turns open and safer to have it ready to shut off...the less chances taken the better..ive had some teachers with 50 yeaars of experience and i'll opt to listen to what they've learned and share with me..
Reply:Many times a person might see two nearly identical (in appearance) flow safety devices attached in line with their O/A rig, one at the hose side at the regulators and one at the torch valve body. If so and if they were installed as is with no special adapters, the one at the output at the regulator should be a 'check valve' and the one at the torch valve body would be the 'flash back'. The check valves come off the shelf female-male in the direction of flow and the flash backs come male-female in the direction of flow for ease of installation on any conventional rig and no additional fittings. Plus I believe the fitting sizing is slightly different too. Can't be sure about the sizing without going out to look.  Not saying you couldn't put flash backs at the tank, just that it would require extra effort and fittings.The check valves are put in to to prevent reverse flow.
Reply:I used the acetylene til the tank pressure is 4psi.  i dont know how much is left in the tank and i dont care... that puppy is goin' in to get exchanged/refilled.  i only have flashback valves at the torch, nothing at the regulator, so i'm not going to chance it.