Tank Valve Question

[Ulfhedinn]

I have a set of Thermo modular valves attached to my cylinders. The cylinders are filled with air. I want to unscrew the modular valve plugs on them and install a crossbar essentially making them a set of doubles.

When the valve is turned off is there pressure against that valve plug? I would rather not waste the air and then have to get them refilled. Was hoping to just remove plug, attach crossbar and be on my way.

I am thinking there is no issue but would rather be safe and not have that come off there at 3500PSI

 

[ddmattos]

Yes hence the function of an isolator/crossover bar.

 

[Ulfhedinn]

I'm thinking your meaning is that it is under pressure. So best I use the air first...

 

[ddmattos]

If there is pressure in the tank, there will be pressure against the plug. The crossover bar with isolator allows you to have access to gas in both tank even upon a first stage shutdown. The isolator valve is used when you blow a burst disk or leak from the base of the valve where you need to shutdown a tank in order not to loose gas in both tanks.

 

[Ulfhedinn]

Thanks! Seems that I could use a refresher for that Tech 1 class I started a while back. From the beginning...

 

[BRT]

If you are talking about the yoke to DIN adapters with the allen head center there is no pressure against those.

 

[tbone1004]

what they said, it is the design and one of the only added potential failure point that would cause catastrophic gas loss when diving manifolded doubles. They have to get drained down to absolutely nothing to put that crossbar in. Breathe them all the way down, and hopefully you have a nice dive shop or a buddy that has a transfill whip so you won't have to get them revipped. Try to breathe them down as far as possible because quickly emptying them can cause what little moisture is in that air to condense and that would be bad. Not normally an issue, but something to think about

 

[Akimbo]

Here is a sectional view of a doubles manifold. As you can see, there is always cylinder pressure on the plugs or crossbar regardless of the valve position. The "post" valves only control flow to the regulator ports.

http://www.xsscuba.com/graphics/valves/manifold_lg.jpg