PDA

View Full Version : Oxygen regulator still shows pressure after draining torch



taydin
09-28-2010, 06:32 AM
After I finished using my OA set yesterday, I closed the acetylene valve and drained the torch. Both sides of the acetylene regulator showed zero pressure. Then I did the same for the Oxygen side, closed the valve and drained the torch. But the high pressure side of the O2 regulator shows 20bar pressure, while the low pressure side shows 0.

I first thought this is the same issue I had with the acetylene cylinder, where the valve was leaking. But this can't be the case, because then the input pressure would be 150bars. But it is lust 20 bar. Is the regulator dying?

winchman
09-28-2010, 06:56 AM
I've seen that happen, and found I can get the tank side pressure down to zero by turning the regulator handle in while the torch valve is open, then out after the pressure is relieved.

I used to always release the pressure on the valves on my own O/A outfit, but the ones at the school seem to do just fine being left on overnight, or even for days at a time. I always close the tank valves when I'm trough for the day, but it's impossible to get the youngsters to do that all the time.

MuellerNick
09-28-2010, 07:17 AM
I think this is kind of normal.
What I do, is close the tank, (almost never) drain the hose and close the valve behind the regulator*). If the high pressure rises a bit, I'm not concerned that much. Only if the high pressure shows the tank pressure, there is something wrong with the tank valve.

Just my opinion, I might be wrong.

*)
Not all regulators have that feature, my argon regulator (real flow through; the one with the ball) misses it.

Nick

GKman
09-28-2010, 07:32 AM
I've never seen anyone who preforms the ritual described above putting their car on jack stands after driving. Isn't it the same principal?:p

Your Old Dog
09-28-2010, 08:21 AM
I shut down the main tank valves, open the torch head valves until everything relaxes to 0. I then close the regulators down and then back out the screw until I know I've take some of the pressure off the rubber valve seal. My pressure regulators both stick if left fully out for several days. I've never witnessed any residual pressure on my tanks and I am always watching for it. Tanks that bleed are a little scary to me.

Evan
09-28-2010, 09:13 AM
I have a Victor set that is now about 25 years old. Close the tanks, release all pressure and then close the torch valves. If it is to be left for a while then I back off the regulators. Either way there is zero pressure on both gauges and it stays that way.

Boucher
09-28-2010, 09:15 AM
From your description it sounds like the high pressure gauge is not returning to zero. If it were the regulator there wouldn't there be pressure on the low pressure gauge?

taydin
09-28-2010, 10:27 AM
From your description it sounds like the high pressure gauge is not returning to zero. If it were the regulator there wouldn't there be pressure on the low pressure gauge?

When draining the oxygen hoses, I have the cylinder valve shut, the regulator and torch valves wide open. What seemed odd is that it took a very long time for the hissing to stop. Maybe it didn't even stop and maybe it became so slow that it wasn't audible anymore. At this point, the low pressure side showed zero and the high pressure side was at 20 bar.

Another weird observation (didn't happen before) is that when I cranked up the regulator valve, I clicking and rattling sounds from the regulator. Can it be that the high pressure side has lost its sensitivity, where it properly reduces high pressure O2, but stays shut if the pressure drops below a certain threshold?

taydin
09-28-2010, 10:31 AM
I've never seen anyone who preforms the ritual described above putting their car on jack stands after driving. Isn't it the same principal?:p

Not sure I understand this :confused:

Are you saying I shouldn't bother relesing the pressure? Just shut off the tank, the regulator and torch valves and be done with it?

winchman
09-28-2010, 01:40 PM
In my mind, shutting the tank valves is a safety step that should be done whenever the rig won't be used for a while or whenever it'll be unattended.

I used to think relieving the pressure on the regulator and torch would prolong their life, but that appears to be unnecessary based on what I've seen at the school.

The car on jack stands analogy was lost on me, too.

Black_Moons
09-28-2010, 01:47 PM
Random thing iv noticed: While venting the actylene tank, the output pressure of the regulator goes *up* as the input pressure goes down.

Result? If you had it at 10psi, it might go over 15psi before the tank is emptyed. Allways insure your acetylene regulator is set 'low' (5psi or less) before venting!

MuellerNick
09-28-2010, 02:11 PM
The car on jack stands analogy was lost on me, too.

He forgot to say, that he is releasing the tire pressure.


Nick

Evan
09-28-2010, 03:36 PM
Result? If you had it at 10psi, it might go over 15psi before the tank is emptyed. Allways insure your acetylene regulator is set 'low' (5psi or less) before venting!


The critical pressure for self detonation for acetylene is actually about 30 psi. 15 psi is always used to give a safety margin.

Herm Williams
09-28-2010, 04:20 PM
IMHO after twenty years repairing regulators and torches it does not make any difference, close the tank for safety close the valves on the torch for safety and store the torch. if you have a leak the gauges will go to zero, most welding sets have a small leaks somewhere, most of the time where the regulators fasten to the tanks (small nicks,scratches etc on the seats). Find it with soapy water tighten the fitting to stop the leak or just live with a very small leak. my two cents worth.
re

macona
09-28-2010, 04:22 PM
It's a bad gauge. Most weld shops sell replenishes. Usually under $10.

GKman
09-28-2010, 04:57 PM
I've never seen anyone who preforms the ritual described above putting their car on jack stands after driving. Isn't it the same principal?:p

Because all that weight will wear the springs out!

ADGO_Racing
09-28-2010, 06:35 PM
Because all that weight will wear the springs out!

We actually disconnect the shocks and springs on the race cars, and strap them down to blocks in the hauler.

If we didn't we would put more miles on the shocks and springs going to and from the track, than we do at the track.:D

Black_Moons
09-28-2010, 06:42 PM
Spring wear, Fact or fiction?

I know lots of people mention 'replaceing' the shocks in a car after so many miles as the suspension becomes.. 'loose'?.. Poor in any respect.. Not sure if its the springs fault, or the dampeners however..

Toolguy
09-28-2010, 06:47 PM
When springs wear, they sag. The car sits lower. When shocks wear, the car continues to bounce up and down after a bump. It's like riding in a rowboat.

Evan
09-28-2010, 07:53 PM
Springs wear all right. You haven't been over the Yanks Peak 4x4 trail. There is a 15 kilometre section called the twister as it will twist your frame and while it's at it break the springs. It broke one of the front coils on my Ranger about a week after that outing. Spring steel accumulates fatigue damage when it is repeatedly stressed over approximately one half the yield point. Below one half it is considered to not accumulate fatigue at all. The closer to the yield point the faster the fatigue builds up until it fails at some value well below the yield point. As the fatigue accumulates the yield point moves downward.

jdunmyer
09-28-2010, 08:01 PM
Any book I've read on torch use says to shut down a set:
1. Close the tank valves.
2. Open one of the torch valves, vent the pressure, close the valve.
3. Repeat (2) for the other gas.
4. Back out both regulator screws.

Note that torch valves should be left closed, and regulators backed off. Only open/set a regulator AFTER opening the tank valves. Remember also, Oxygen tank valve is to be all the way open, Acetylene should be about 1/2 turn open, almost never more than a turn.

Some regulators will be ruined by having the screw 'in' when opening the tank valve. The fact that many people never back off the regulators doesn't make it right.

See: http://www.cust.educ.ubc.ca/tsed/Students03/corybritton/Web%20Page/Oxy-Acetylene%20Safety.html

macona
09-28-2010, 08:42 PM
Regulators really dont need to be backed off before turning them on. In industrial applications they use identical regulators on fixed systems and instead of a handle they have a screw with a locknut. Nobody goes around and unscrews them when the bottle is changed.

If a regulator is going to fail it wont matter one bit wether the handle is screwed in or not. And if it does fail, like one did here two days ago, there are safety overpressure releases on the LP side either on the diaphragm or the body.

Not standing in front of them is a very good idea, especially if some idiot oiled the threads on the O2 bottle.

Letting the pressure out after you are done is nonsense as well.

wierdscience
09-28-2010, 08:49 PM
Another vote for shutting the valves off and going home.

Boucher
09-28-2010, 09:21 PM
Marcona said: "Not standing in front of them is a very good idea, especially if some idiot oiled the threads on the O2 bottle."
Years ago I was shown the X-Ray of the wound channel and the stem from an Oxygen regulator that went up a guys arm when he turned the bottle valve on. I don't remember why they said this happened but since then I have never opened an Oxygen valve with my arm in front of that stem.

They also showed the aftermath of an explosion that occurred when a new bottle was turned on. Failure Analysis found the wing of a bee between the nut and the stem. The bottle had been hauled standing up and the bee went in the hole in the cap and into the Oxygen valve. Before attaching the regulator it is good procedure to crack the Oxygen valve very carefully and slowly to purge the valve clean if there is anything in there. Amazing failure analysis with the way things looked it is surprising that they found the nut much less the wing of that bee. The back of the building looked like satchel charge exploded there.

macona
09-28-2010, 09:39 PM
Anything organic with high pressure O2 becomes explosive. Always check the openings before installing the regulators. Its not uncommon to see wasps try to set up camp in bottle caps.

I do have some lube that can be used with O2 service. Its called Krytox. Its a Teflon based lube that is speced as O2 compatible. The stuff is something like $100 for a little 2 OZ tube (Krytox 240AC). Its also good for seals in highly corrosive environments like Florine.

I also use Krytox LVP for my vacuum system. Beats the old vacuum greases hands down.

jdunmyer
09-29-2010, 09:01 AM
Years ago, I worked in a plant where we had an explosion of an oxygen regulator upon opening the bottle. The regulator had been laid on top of an oil drum that had a bit of oil on it and had gotten contaminated. Fortunately, the fella knew to not stand in front of the regulator while opening it, he stood to the side. Regulators are designed to blow out either the front or rear, so standing to the side is the safe way.

Any written procedures that I've ever seen tell you to back off the regulators after purging the hoses. Regulators should always be backed off when opening the cylinder valves. Here's a procedure from the Victor torch people:
http://www.thermadyne.com/IM_Uploads/DocLib_2879_56-0114%20guide_lo.pdf
They recommend backing off regulators when the torch isn't being used. They also recommend opening the Acetylene valve no more than 1 1/2 turns. I've seen "Internet Experts" recommend opening the Acetylene valve wide-open, same as the Oxygen. Victor's recommendations are probably better than the I.E.'s.

taydin
09-29-2010, 10:21 AM
When I exchanged my acet cylinder, the guy told me about an incident where he took an O2 bottle to a shipyard. They placed the O2 bottle, standing, near a railway track. The bottle fell over, the valve hit the rails and was knocked off. The O2 bottle became "mobile" and traveled a few 100 meters until it ended up in the sea, not to be recovered. Could have been worse :eek:

Fortunately, my O2 bottle has a thick ring around the valve and the ring is welded with several rods to the bottle. So in an event of a fall, the valve should be protected.

Evan
09-29-2010, 01:25 PM
The reason for not opening the acetylene valve very far is to limit the escape rate of the acetone in the event of a regulator failure or other similar accident. Acetylene is stored in the bottle dissolved in acetone just like CO2 dissolves in water to make soda pop. Also just like soda pop if you suddenly crack the cap off the dissolved gas will come out of solution in a big hurry.

In an acetylene bottle if the gas begins to escape too quickly the acetone will start to boil but when it gets to the very slightly open valve it acts as a restriction to maintain the pressure in the bottle since it won't pass fluid near as fast as gas. It doesn't take a catastrophic failure for this to happen. If you are using a large rosebud or other tip that uses a lot of fuel gas it is possible to exceed the maximum withdrawl rate of acetylene from the tank. The maximum rate of use should not exceed 1/7th of the tank capacity per hour. Obviously, the smaller the tank the smaller the flow rate allowed.

EddyCurr
09-29-2010, 01:48 PM
... the guy told me about an incident where he took an O2 bottle to a
shipyard. They placed the O2 bottle, standing, near a railway track. The
bottle fell over, the valve hit the rails and was knocked off. The O2 bottle
became "mobile" and traveled a few 100 meters until it ended up in the sea,
not to be recovered.A video demonstrating what happens when valves are broken
off different styles of oxygen cylinders.


Scuba Tank - Valve Cut (http://www.youtube.com/watch?v=tyINNUaXa8Q)

.

jdunmyer
09-29-2010, 03:14 PM
The reason for not opening the acetylene valve very far is to limit the escape rate of the acetone in the event of a regulator failure or other similar accident. Acetylene is stored in the bottle dissolved in acetone just like CO2 dissolves in water to make soda pop. Also just like soda pop if you suddenly crack the cap off the dissolved gas will come out of solution in a big hurry.


The reason I've always heard as to why "only a turn or so open" on the Acetylene cylinder is in case of a fire in the hose. You can get the tank valve closed in a hurry, instead of having to wind & wind on a wide-open valve.

The Oxygen cylinder is always opened fully so as to seal on the outward seat. This prevents packing leakage due to the extremely high pressure.

Evan
09-29-2010, 05:00 PM
You won't get a fire in the hose but if you did the flame speed will be about 5 feet per second. There isn't much chance of getting to the valve to close it in time. It doesn't matter though. It won't simply burn without oxygen. The entire acetylene storage and distribution system is very carefully designed to prevent detonation of the gas. Acetylene is unique from other common flammable gases in that it is inherently an unstable chemical a lot like nitroglycerine. If it is subjected to a compression shock wave it will explode in a detonation reaction, not burning. The ability to detonate is dependent on the amount of free space available for the gas to form at least one detonation cell. Every explosive gas has a characteristic detonation cell size that is dependent on the chemical makeup of the gas. The cell size is pressure and temperature dependent. By limiting the free space available for the gas to occupy at the planned working pressure to less than 50% of that cell size it cannot be detonated unless the pressure exceeds a particular value.

Instead of a fire if a flashback occurs and creates a strong enough pressure wave it will travel up the hose as a detonation shock wave at about 3000 metres per second. When it gets to the regulator it will blow it apart which is why flashback arrestors are a very good idea. Because the acetylene is stored dissolved in a solvent it will not detonate in the tank unless the tank has been run low on solvent.

If the flashback blows the regulator off the tank that is when the slightly open valve helps to limit the ensuing fire. If the valve is wide open enough acetylene may escape to create a secondary detonation of far larger proportions.

BTW, I am trained on industrial gas handling so I can fill in for my wife if necessary at her place of work. She sells industrial gases.