Unable to Remove Valve From Tank

[maxdeeep]

Its been a year and we need to VIP some of our cylinders. One so far has resisted all of our efforts to unscrew the Valve from the Cylinder. Yes, ALL the air has been vented from the cylinder! We are talking about a new aluminum 80 with a thermovalve 200bar Din/Yoke convertible valve with a viton tank o-ring used in salty ocean waters. Soaking the tank in hot fresh water and applying some serious force with an appropriate sized wrench (spanner ot some) has left us pretty frustrated.

Any Ideas? This valve has got to come off or the cylinder is toast.

Curt

 

[tc]

Rubber mallet.

 

[Scared Silly]

Good chance there is galling. Have you clamped the cylinder and tried a cheater bar on the valve?

 

[Scott]

Tank vise, rubber mallet and remember righty tighty, lefty loosey

 

[tfsails]

Sometimes a reluctant valve is an indication of a tank that still has air in it. This can be VERY DANGEROUS OR EVEN FATAL if you try to remove the valve. Try removing the burst disc to make absolutely sure that the tank is empty. It's possible (but not very likely) the tank valve may not allow the air in the tank to all drain out. Removing the burst disc bypasses the valve and removes it from the equation.

Another idea: to insure that no foreign object is blocking the valve assembly inlet inside the tank, try putting another 100psi back into the tank to blow any FOs from the valve. I would think this action would take care of that possibility.

Most likely, though, the threads are galled and therefore almost impossible to turn. If this has happend, I'd suggest junking the tank.

 

[Stu S.]

If the viton o-ring is intact, then it is doubtful that corrosive sea water got into those threads.

Here is a last-ditch idea. Remove the burst assembly and squirt in about a third of a can of WD-40, or similar. Put the burst assembly back in and close the valve. Turn the tank upside down so that the WD can penetrate the threads. Wait two days and put a wrench on that valve and hit it with a mallet.

If that works, you'll have some cleaning to do, and need a valve rebuild. If it is headed for the trash anyway, why not?

 

[rcs9250]

If you never saw air bubbles coming out of the valve/tank interface chances are it is not stuck as a result of water going in to the cylinder. Most times it is the tank/valve surfaces in contact with each other that are the problem. If you do not have the means of locking the tank so it absolutely doesn't move while wrenching take it to a hydro facility that does larger cylinders with tapered threads. They will have a tank vise that will hold it still. They will also have the appropriate wrench for the job. It may even be mechanized.
If the hydro facility isn't an option people have strapped them to telephone poles etc.
I have heard of people jacking up a tandem axle trailer and then putting the cylinder between the two tires and then lowering the trailer to lock it. Obviously don't do it with a Terex off road dump truck or the tank will be compromised(flat). Typically a boat trailer will do. You most likely will have to apply the brakes to keep the cylinder from driving the tire.
Good luck. Let us know what worked.

 

[James Bond boat entry]

Fill the tank, then open the valve wide open to cool the metal (metal shrinks when frozen) then unscrew it while it's still cold.

 

[rjack321]

Dribble some penetrating oil into the gap between the valve and tank. AL80s like to corrode in this space outside the Oring. Might take a couple applications but it will loosened the corroded bond.

Its highly unlikely that moisture penetrated the oring seal and got into the actual threads.

 

[Davidstealey3]

Sometimes a reluctant valve is an indication of a tank that still has air in it. This can be VERY DANGEROUS OR EVEN FATAL if you try to remove the valve. Try removing the burst disc to make absolutely sure that the tank is empty. It's possible (but not very likely) the tank valve may not allow the air in the tank to all drain out. Removing the burst disc bypasses the valve and removes it from the equation.

Another idea: to insure that no foreign object is blocking the valve assembly inlet inside the tank, try putting another 100psi back into the tank to blow any FOs from the valve. I would think this action would take care of that possibility.

Most likely, though, the threads are galled and therefore almost impossible to turn. If this has happend, I'd suggest junking the tank.

this is probally the best thing you can do. the only things i can add is removing the knob from the valve and removing the plug from the inside the opens and closes the valve. next you can get a wrench and put a wrap or two of tape on it to protect the valve and put the tank in a vise of some sort. then gently hit the end of the wrench with a rubber mallet to try to loosen the valve. if this does not work i wouldnt try anything else.
we had a tank come into the shop from a hydro and the valve was so tight we were spining it in a makeshift vise to get the valve out. they had to take it back to the people that did the hydro to remove the valve. i think it was the biggest guy at the place that put the valve on and used his body weight to do it.