# Oxy acetylene regulator question



## Barncat (Nov 27, 2021)

I am either having a regulator problem or a set up problem. For oxygen, I turn on slowly, open a full turn or two, then set regulator to about 40psi.  When I hit the lever to start cutting, it drops to about 20psi? Is that normal? Do I set the regulator with no gas flow and then leave it? Also, during use, the flow slowly creeps up. After a couple of cuts, the regulator had increased to about 100psi. Am I doing something wrong, or does the regulator need a rebuild?


----------



## cathead (Nov 27, 2021)

The regulator is supposed to keep the pressure at a certain pressure level.  If it isn't doing it, 
it must be defective.  The proper procedure for opening an oxygen bottle is to open it slowly
and completely until it hits the stop to ensure that there are no leaks.


----------



## addertooth (Nov 27, 2021)

This can also happen if your main gas valve on the oxygen cylinder is not WIDE open.  Some people only open the cylinder valve a turn or two, and experience pressure drop under operation.


----------



## LucknowKen (Nov 27, 2021)

Barncat said:


> open a full turn or two, then set regulator to about 40psi.


FWIW I was taught to always fully open the tank valve.


----------



## brino (Nov 27, 2021)

cathead said:


> The proper procedure for opening an oxygen bottle is to open it slowly
> and completely until it hits the stop to ensure that there are no leaks.





addertooth said:


> This can also happen if your main gas valve on the oxygen cylinder is not WIDE open. Some people only open the cylinder valve a turn or two, and experience pressure drop under operation.





LucknowKen said:


> FWIW I was taught to always fully open the tank valve.




Very interesting!

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......

My initial take on the first symptom here (pressure drop 40-20psi) when cutting was that the O2 bottle was empty or nearly so.
However that cannot explain the pressure creep to 100psi.

-brino


NOTE: PLEASE READ!
I have it backwards here in this post!

Please see all the correct answers below and my update at post 29 in this thread here:
https://www.hobby-machinist.com/threads/oxy-acetylene-regulator-question.96504/post-901927


----------



## addertooth (Nov 27, 2021)

I missed the part on the creep to 100 psi.    That latter part sounds like regulator issues for sure. Extra Pressure has nowhere to come from, other than the regulator.   
Also, make sure the regulator is RATED for oxygen.


----------



## b4autodark (Nov 27, 2021)

brino said:


> Very interesting!
> 
> 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.
> ...


Always open O2 bottle valves fully as they are double seating valves and are designed to seat in the open position to prevent leakage around the stem.


----------



## Barncat (Nov 27, 2021)

It is an o2 specific regulator I believe. I was taught only open the acetylene a 1/2 turn, and about 2 on the oxygen


----------



## Barncat (Nov 27, 2021)

I will try with the oxygen fully open and see if that changes. Hoped have some time this weekend to try. So I set the regulator with no flow at the torch, correct?


----------



## LucknowKen (Nov 27, 2021)

brino said:


> My night class at the local community college for oxyacetylene welding said to never open the O2 bottle valve fully.


I would wonder why.
I was told (more than 30 yrs ago) that when the valve was fully open it acted as an anti flashback device.
Would like to know if this is true.


----------



## b4autodark (Nov 27, 2021)

Barncat said:


> I will try with the oxygen fully open and see if that changes. Hoped have some time this weekend to try. So I set the regulator with no flow at the torch, correct?


You want to have flow when adjusting the regulator.


----------



## b4autodark (Nov 27, 2021)

LucknowKen said:


> I would wonder why.
> I was told (more than 30 yrs ago) that when the valve was fully open it acted as an anti flashback device.
> Would like to know if this is true.


No, that is not true. If it were arresters would not be required before the mixing barrel.


----------



## jcp (Nov 27, 2021)

brino said:


> Very interesting!
> 
> 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.
> ...


This IS interesting! I was taught just the opposite! This was in the mid '60's. Instructor at the local college explained that the acetylene bottle was to be opened no more than two turns in case you needed to shut down the flow quickly......as in doing something stupid like burning through the hose or letting it come in contact with freshly torched material. He had been teaching a long time and probably had some exciting  experience to draw from....like someone knocking over the oxygen bottle, which broke off the valve, and having the bottle escape the building by crashing through a wooden door that opened out onto the alleyway.


----------



## C-Bag (Nov 27, 2021)

jcp said:


> This IS interesting! I was taught just the opposite! This was in the mid '60's. Instructor at the local college explained that the acetylene bottle was to be opened no more than two turns in case you needed to shut down the flow quickly......as in doing something stupid like burning through the hose or letting it come in contact with freshly torched material. He had been teaching a long time and probably had some exciting  experience to draw from....like someone knocking over the oxygen bottle and having it escape the building by crashing through a wooden door that opened out on the alleyway.


I was taught the same thing almost 50yrs ago. Since I never use the cutting torch I don’t need that much pressure. I did have to put a kit in one of my regulators after 20yrs of use because it started acting up.


----------



## ddillman (Nov 27, 2021)

I was always told fully open the oxygen and one turn on the acetylene. also always set the regulators with no flow.


----------



## Janderso (Nov 27, 2021)

You would think our instructors in the 70’s would have the same information to teach.
I was taught, double seal on the oxygen = open all the way.
Acetylene, 1/2 to one turn Only.


----------



## Janderso (Nov 27, 2021)

ddillman said:


> I was always told fully open the oxygen and one turn on the acetylene. also always set the regulators with no flow.


I was taught to adjust the regulators only while flowing as this is your working pressure.
Interesting indeed.


----------



## b4autodark (Nov 27, 2021)

Janderso said:


> I was taught to adjust the regulators only while flowing as this is your working pressure.
> Interesting indeed.


For what it's worth I was a welder for 40 years and taught night school welding for pipe trades for 22 years. Either I know what I'm saying or I've been doing it wrong all those years. Open valve fully on the O2 and 1/2 to 1 turn on Acet and adjust with flow.


----------



## Janderso (Nov 27, 2021)

b4autodark said:


> You want to have flow when adjusting the regulator.


So we agree Right?


----------



## b4autodark (Nov 27, 2021)

Janderso said:


> So we agree Right?


Correct


----------



## RJSakowski (Nov 27, 2021)

"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 (Nov 27, 2021)

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 (Nov 27, 2021)

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 (Nov 27, 2021)

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 (Nov 27, 2021)

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 (Nov 27, 2021)

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


----------



## cathead (Nov 27, 2021)

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 (Nov 27, 2021)

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 (Nov 27, 2021)

brino said:


> 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 (Nov 28, 2021)

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.


----------

