I was taught...Acetylene is 1/4 turn or whatever needed to turn it on. Other tanks all the way on.

 

That's pretty much what the manual for the Tweco 211i says. I was just reading it last night. They say to only turn Acetylene valve 3/4 to 1 1/2 turns only but to turn all other gas valves all the way on until they seat against the gland nut to prevent leaking. Acetylene is lower pressure than most gasses so I suppose that's why they don't need to seat the valve.

And YES the Tweco is not an oxy-acetylene welder but the manual still talks about valves on acetylene tanks.

 

High pressure bottles should be opened all the way and upper
seat (stem seat) snugged up. Acetylene bottles opened less than
a full turn. At least that's what I was told at the welding school l
attended many years ago. Both should be opened slowly.

 

This is what I was taught too; open most bottles all the way so that the valve seats against the upper stop to prevent leaks. The exception is that fuel gases (I was taught all fuel gases, not just acetylene) should be opened just enough to get the gas flowing so that if you have to turn them off in an emergency, you can do so more quickly.

 

what's the story with the acetylene gland nut? after opening the tank the other day i smelt gas and thought it was coming from the valve. i tried to tighten the nut just below the valve hand wheel but it was either already screwed down all the way or stuck. has anyone here had problems with this?

 

I now have my second acetylene bottle in a row with a defective valve.

 

3/4 to 1 turn only for me.

A thread discussed this a tad back. Modern seals should not leak and do not need to be opened all the way. It is more common for the seats to leak IMO but I have seen leaky o-rings a time or two. See Dave's post #20. http://weldingweb.com/showthread.php?263271-How-far-do-you-open-an-Argon-tank-valve.

 

3/4 to 1 turn only for me.

Same here.

this might be the one guys lean on like their life depended on it.

https://www.youtube.com/watch?v=3psf5hWZtZc

 

It changed a while back. In the 80's I was taught the same as most people to back-check the high pressure valves.

All the way open is no longer the requirement.

Here is a thread I started on the matter some time back that explains:
http://weldingweb.com/showthread.php?268311-High-pressure-tank-valves-with-o-rings&highlight=

 

MinnDave is right , HOWEVER, IF you are not sure if your particular tank valve is the newer style, open it up and soap it. Just mix some water and '' Dawn '' is what I like into a spray bottle and test it.You could even pass a brush around it to build soap up. I always have a spray bottle with water and Dawn in it. Besides for leak checking great to wash your hands with.

 

Or get "Smartop" tanks, one flip and forget about it. No worries if you are unsure if they are left on.

 

In industrial gas applications (lab use) i was always taught to open fully then back off 1/4-1/2 turn. This solves the problem of someone trying to open an already fully opened valve and breaking something off thinking it is stuck closed (and getting out a wrench/cheater...). Since it will move a little in either direction, they will realize it was fully open and not force it. In theory...

 

exactly the same what I was told for breathing air (rescue, not diving). the breathing air was 300bar, which is 60% more pressure than what an Ar tank has.
He or H have the same pressure whether used in the lab or for welding. so, I really have my doubts if theer is a technical need for the second stop for at least 2 or 3 decades...

 

Acetylene tank turn it about half a turn, be sure you are not facing the valve, oxy/ tank all the way.

 

I never have any valve all the way open to the stop. 1/4 turn off or more for me. I've seen people come to a fully open valve and thinking it was closed tightly, crank it counter clockwise trying to get it 'open', messing up the valve and never getting it to seal again. I've seen this cost replacement of oxygen valves costing several thousand dollars more than once.
If it's 1/4 turn off from full open, the attempt to open is going to get some motion before hitting the stop.
The flow rates you're going to demand from a high pressure tank are not going to require every last bit of valve opening.
There may be some worn valves that leak through the stem from loose threads but that's a whole different thing.

 

From my other thread:

 

From my other thread:

View attachment 1613411

The next question is how do you know if it's an O-ring valve?

 

The way I was taught was
Open the oxygen valve SLOW or you can get a "blowback" fire or something like that if you left oxygen pressure in the regulator (I heard), then open the oxygen all the way open and snug it to seat the seal at the "open" end.
Argon, CO2, etc. should also be snugged "open" to prevent leakage.
Acetylene open just enough to get flow. You want to be able to close it in a hurry if need be.

 

A much forgotten safety tip is to, with your safety glasses on and not reaching over the gage, stand beside or behind, and not in front of the gage when opening the valve slowly as when a gage fails the glass and brass fly out the front.

 

Opening pure oxygen slowly, what I've been taught and it kind of makes sense is that in the three sides of the combustion triangle, you already have Oxygen. Opening the valve quickly may create friction within the valve, or a temperature rise from the rapid flow of Oxygen through the valve as it fills the dead space within the lines, giving you the second of the sides of the triangle. Possibly the tiniest bit of contamination, or the rubber line, o rings, themselves could give you the fuel that might otherwise not be a problem.

 

It's called adiabatic compression heating. Modern valves are designed to tolerate this so opening slowly is not needed, but doesn't hurt anything. It's part of the standards that manufacturers of valves must comply with.

This is how they test it:
http://www.wha-international.com/adiabatic_compression.php