Valve leak question

[Splitlip]

I have modular thermo Valves on my steel tanks.

This past weekend while gearing up I had an explosive rush of gas coming out of the hand wheel in one of the bottles. In the couple of seconds it took to shut it down I lost about 300psi.

I played around with it for a minute or two and all I could find was the thermo nut was loose. I tightened it down, opened the valve and no more leak.

I thought the thremo nut was only there to retain the hand/thumb wheel. If that were the case, why did it seem to cause the leak? Or why did snugging it down seem to solve the problem?

I was under the impression I could remove the nut and hand wheel with no adverse effect other than difficulty opening and closing.

I would think rather the bonnet nut could cause the problem.

Is it possible the loose thermo nut allowed the bonnet nut to back out? Or is the bonnet not tight but being held by the thermo nut and spring?

I am thinking I need to pull the wheel and tighten the bonnet.

Or am I off the mark?

Thanks.

[CompuDude]

I read about a few failures like that in this thread on TDS: The Deco Stop

So I don't think you're alone. It's not common, though.

[jbres1]

The valve has a few seating surfaces that hold the pressure inside the tank.
1- the valve seat. When the seat is against the valve body it seals off the flow.
2- the stem to bonnet nut surface. There is an o-ring and a teflon ring that seal the stem area. The pressure inside the tank helps to push the stem shoulder up to the bonnet that forces the o-ring and teflon stem seal to seal the mating surface. If for some reason the stem gets pushed in, the seal is broken and the pressure can blow past the seal.
If you regain the seal, the flow stops. These seals are dynamic seals.
3- The copper crush washer is a static seal between the body and the bonnet nut.

So in your case you were able to regain a seal when you turned the valve off and tightened up the handle nut, thus putting the seals in contact withthe shoulder of the stem and bonnet nut.

Hope this helps, Jim .

[Splitlip]

Thanks guys

[captain]

If the bonnet nut is loose it will leak but only when the valve is open. When the valve is closed there is no pressure under the bonnet nut.

[Splitlip]

Originally Posted by captain

If the bonnet nut is loose it will leak but only when the valve is open. When the valve is closed there is no pressure under the bonnet nut.

It only leaked when the valve was open. Just funny that it stopped leaking when I tightened the retaining screw. In the DS link compudude posted, one of the guys described an issue with a loose bonnet nut. I am thinking that when pressurized all the other "seals" in the system made it tight.

The other tank and valve I purchased at the same time also had a loose retaining nut.

Tomorrow, I am pulling both wheels to get to the bonnets. I could only get the retaining screws so tight without borrowing a notched flat head driver. Now I cannot get them loose. A buddy has a spanner that works. Bringing it by.

[cummings66]

I had a buddy have that happen to him too, so it's not exactly uncommon and it's usually an easy fix.

[jbres1]

Will you be working on the handle only or the bonnet nut ?
I ask because , the bonnet nut may be under pressure so be carefull. No volume to speak of, but the bonnet nut also is there to keep the seat from un-screwing too far.
Also be aware that the o-ring in the stem area may have extruded when the pressure rushed past it during the blow by. If you are going to work on the valve without pressure in the cylinder, you may want to remove the bonnet nut and chect out the o-ring.
Here is a link to a blown up view of the typical valve assembly.
Thermo Valve Parts @ DiveSports.com

The handle nut has a spring below it that pulls the stem shoulder up in contact with the seating surface of the bonnet nut.
For the screw driver with the slot, I went to my local Sears hardwarestore and purchased a short wide screw driver and then filed a slot in the center to allow the stem threads to go into the slot.

Jim breslin

[Splitlip]

Thanks Jim.

I will be careful. I plan to make myself a driver this weekend.

Will probably end up dumping gas to inspect too.

[awap]

With the valve closed, I have disassembled everything up to the seat. Your leak is probably some corrosion on the stem. Your tightening of the spring retainer probably repositioned the seating surface just enough to restore the seal, for a while anyway. When you remove the packing nut (aka bonnet nut) it is best to have a new copper crush washer on hand, although I have had some luck reusing them as some brands require torque in the 25 - 30 ft-lb range. I expect you will need to clean the stem and replace the stem o-ring. Best to replace the plastic washer and copper washer while you are at it. Of course, if you drain the tank, you can inspect/replace the seat while you are at it.