Ominous tanks leak?? Help

[kotik]

Yes it would be.

OMG-- yes, of course it would be, otherwise you'd lose half your gas when shutting down a post.

Sorry folks, it was really late/early when I wrote that....

 

[idive2]

So with the iso valve open air is kept from escaping by the o-rings on the valve. With the iso valve closed air
is being kept on one side by a seat but the o-rings would contain the air from escaping from the other tank ?
Am I close to following this correctly ? Either way seems like the iso valve is in need of repair. It is nice to
to know how one tank could be down and the other one is not if the valve is sealing in a way that is being
discussed.

 

[halocline]

So with the iso valve open air is kept from escaping by the o-rings on the valve. With the iso valve closed air is being kept on one side by a seat but the o-rings would contain the air from escaping from the other tank ?
Am I close to following this correctly ? Either way seems like the iso valve is in need of repair. It is nice to
to know how one tank could be down and the other one is not if the valve is sealing in a way that is being
discussed.

Yes, that's right. Think of it this way, a tank valve stops air from exiting the tank with the seat, and any air downstream of the valve seat is open to ambient pressure via exit hole in the valve. Put a regulator on the valve and open it, and you now have high pressure air downstream of the seat. That's why when there's a leak in the valve stem o-rings there are bubbles coming out the valve handle, but not when the valve is closed.

The iso valve appears to be the same sort of valve, but there is always high pressure air on both sides of the seat. So even with the iso valve closed, HP air can leak out the stem o-ring from one of the tanks. That's what's happening in the video.

In order for the iso valve to seal off both tanks with a high pressure seat, you'd need either two seating surfaces, like a ball valve, or two orifices and maybe a double-sized seat of some sort. I'm actually pretty surprised that they're not designed that way. Plus, a simple ball valve type handle would immediately rid of any confusion about whether the iso valve is open or not, even by feel. My guess is that ball valves must not have the same reliability at high pressures or would be too expensive to design for this application.