Oxy acetylene regulator question

[RJSakowski]

"Modern Welding" by Althouse, et. al. states that oxygen cylinders have a double seating valve and should be fully opened to prevent leakage around the stem. It further states tha acetylene cylinders should be opened 1/4 - 1/2 turn to permit rapid shutdown in the event of an emergency.

Altogether, I had been a participant in the educational system for 21 years and I learned to take information from instructors with a grain of salt. More than few, including college professors spoke out of their nether orifice. Particularly in the case of vocational school instructors, a good portion of their knowledge came from personal experience, much of which came from fellow workmen.

A parable that I like to quote is about a young housewife cooking a roast for Sunday dinner. She took the roast and cut each end off before she put it in the roasting pan. Her young daughter asked her why she did that and she answered" because Your grandmother always did that. Later that day when the family was gathered at the table with the grandparents, the young lady ashed her grandmother why she cut the ends off the roat before roasting. Her grandmother said. "because that's what my mother always did". The young lady, now curious, called her great grandmother that evening to ask her why she cut the ends off the toast before roasting. "Oh", her great grandmother replied, "the roast was always too big for the pan so I cut the ends off so it would fit".

It is easy to get caught up in tradition and not understand the basis for the tradition. Furthermore., when tradition gets passed from one person to another, distortions can occur, resulting in a final result completely alien to original message. In my mind, the best way to determine proper opening of a gas bottle is to get the manufacturer's recommendation. The best way to determine proper setting of OA cutting torch pressure is to get the torch manufacturer's recommendation. Anything else is hearsay and should be treated as such. As a former employer was fond of saying,"trust but verify".

 

[WobblyHand]

Agree with @Janderso and @b4autodark. I was told by my welding instructor that the reason for the partial "cracking of the valve" for acetylene was that acetylene can become unstable at high discharge rates. Like if you put a huge rosebud tip running off a small tank. (Don't ever do this!) Really a safety thing, to help keep the acetylene safely dissolved in the the carrier fluid, which I believe is acetone. When acetylene is dissolved in acetone it is stable at low discharge rates. High discharge rates can also draw out the acetone from the tank, which destabilizes the acetylene in the tank. I believe the standard is now to have the discharge rate no greater than 1/10th the capacity of the tank per hour.

Quoted from: What you need to know about acetylene

The 1/7th rule has been the standard for many years, but was updated to 1/10th to further minimize the withdrawal of liquid solvent (see Compressed Gas Association G.1 5.3.3.13):​

To minimize the withdrawal of liquid solvent, acetylene should be withdrawn from the cylinder at a rate not to exceed one-tenth (1/10) of the capacity of the cylinder per hour during intermittent use. For full withdrawal of the contents of the cylinder on a continuous basis, the flow rate should be no more than one-fifteenth (1/15) of the capacity of the cylinder per hour.​

It’s very important to follow this rule of thumb in order to safely withdraw acetylene from the cylinder. If the flow rate exceeds the recommended flow rate, you’ll start to pull acetone through which can cause the acetylene to reduce. If acetylene reduction occurs, this can cause the acetylene to become very unstable and potentially explosive. Additionally, acetone damages plastic and rubber, so it can damage torches, regulators and the hose used to dispense the gas if the solvent passes through.​

Also was taught that the O2 tank was to be cranked all the way open to the stop to prevent stem leakage.

 

[DAT510]

Here's a decent webpage about gas welding safety, Tanks, Valves, Regulators etc.

Preparing a Fuel Gas Welding System for Operation

Welding is a method of joining metal parts and structures by fusion with or without the use of a welding rod. Every airplane depends on welding for adding strength to some parts of its structure.

www.acornwelding.com

 

[RJSakowski]

As to seeing an excessive pressure drop when the torch cutting is opened, another possibility is that the regulator is undersized for the torch being used. Some of my larger torches are capable of cutting 12" of steel and there is a total mismatch of the torch orifice size and the regulator size. O2 tanks have comparatively large orifice and are not likely to be the flow limiting factor, even if opened a couple of turns. OTOH, a regulator functions by opening an orifice just enough so the flow rate balances with the line pressure. By nature, there will always be a pressure drop with increased flow rate. A better regulator will minimize this.

However, the creeping pressure is positive indication of a defective seat in the regulator. It could just be a matter of some dirt on the seat which can be sometimes cleared by removing the line and opening the pressure to a maximum stetting and then cracking the tank valve. The resulting burst would blow the contaminate out. In more stubborn cases, the regulator would have to be disassembled and cleaned.

 

[b4autodark]

While on the subject I feel it should be mentioned that the proper way to open ANY cylinder valve with an adjustable regulator attached is to make sure the adjusting screw is backed all the way out so there is no flow when the bottle valve is opened.

I remember a safety poster hanging in the welding classroom put out by Smith torches showing a cartoon picture of a worker holding a torch with one hand while the other hand was on the oxygen bottle valve, the regulator adjusting screw was behind him flying off into the sky, you could see it through a fist sized hole in his chest. Two co- workers were standing nearby, one was speaking and the caption was "Earl forgot to back off the regulator screw". Even though it was a cartoon, I could always see the image in my mind every time I turned on a cylinder.

 

[Barncat]

Thanks for all the replies everyone. I have some things to try next time I can make it to the garage.

 

[cathead]

Acetylene bottles are not supposed to opened fully from what I understand. If you have a fire following up the hose,
you can quickly shut the acetylene valve and save yourself from disaster. I open mine about a half turn for that reason.
I didn't take any classes, just learned most of what I know by osmosis....

 

[Dave Smith]

oxy valve always fully open to seal, and acetylene valve only 1/4 turn with wrench left on valve for quick emergency shut off---has always worked good for me. Dave

 

[brino]

My night class at the local community college for oxyacetylene welding said to never open the O2 bottle valve fully.
Full-open for the acetylene, but that was nearly 30 years ago now.
I will have to check some other sources, too.... not that I don't trust you guys......

I was very wrong!
Perhaps I mis-remembered; and I have very likely done it wrong on occasion!

According to:

The Oxy-Acetylene Handbook, Linde copyright 1943, chapter 3 Oxygen and Acetylene, page 37:

Do not open an acetylene cylinder valve more than one and one-half turns.... Always leave the T-wrench or key in position ready for immediate use, so that the acetylene can be turned off quickly in case of emergency.

Welding Skills and Techniques,Robvert P. Schmidt, Rston Publishing 1982, chapter 1 Oxy-Acetylene Welding and Cutting page 19 "How to Light a Torch":

Open the oxygen cylinder all the way, SLOWLY. Do not stand facing the gauge, stand to one side in case the diaphragm ruptures.Turn the regulator screw in until the gauge read about 5psi. Open the torch valve to fill the line and shut off the torch valve. Slowly open the acetylene valve one-fourth to one-half turns. IN case of fire it is easier to shut off the cylinder. Turn the regulator screw in so that the gauge reads about 5psi. Open the torch valves to fill the lines and then shut off the torch valve.

Welding Skills, Giachino and Weeks, American Technical Publishers, 1985, Oxyacetylene Welding - OAW, Chapter 6, page 65 "Lighting the Torch":

Open the acetylene cylinder valve approximately one complete turn and the oxygen all the way. Next turn the oxygen and acetylene regulator adjusting valves to the required working pressures."

Welding, Third Edition by James A. Pender, McGraw-Hill 1986, page 53:

Open the oxygen cylinder valve and the acetylene cylinder valve slowly. Remember to open the oxygen valve all the way and the acetylene valve one and on-half turns.

I will update my previous comment to point here.

Thanks for all the feedback.
Great question and discussion!

-brino

 

[aliva]

Well I may as well throw my 2 cents in this discussion. I've been a millwright for over 30 years some my training and practice has been O2 open fully because of the double seat in the valve, Acetylene open 1/2 turn incase there is is a fire its quick to shut off. Don't worry if you have O2 leak it's not combustible, it only supports combustion Flash back arrestors are attached to the torch mixer never at the tank. If a flash back occurs it's going to be at the mixer, since the O2 is at a higher pressure it could force any flame up the acetylene hose. Acetylene cylinders are normally stored in the vertical up right position. If at anytime the cylinder has been in the horizontal position, place it vertically for at least 1/2 hour to allow the acetone to drain back and settle, if this is not done you may get liquid acetone out of the tank instead of acetylene. If pressures are fluctuating at the regulator and you've opened the tanks properly the regulator is probably the culprit, repair the regulator or throw it away and buy a new one. When done with torch shut the tanks off, back both regulators out till zero pressure and relieve the pressure in the hoses and mixer. If you don't plan on using the torch for an extended period of time remove the regulators and cap the tanks.