Isolation Manifold Question

[mahjong]

If there is a failure anywhere at or past (hose, 2nd stage, gauge, etc.) either one of the first-stages, will closing that valve only, without closing the isolation valve, prevent air from the 'other' tank from escaping through that failure point? Or do you absolutely need to isolate the tank with the failure? Here I'm assuming all valves/knobs are in working order and that the failure is at some point in one of the regulators.

Thanks.

 

[T. Bix]

Think of it this way: the isolator keeps the two tanks joined or seperated when opened or closed. The posts control air to the regulators only. so the answer to your question is: the appropriate response to a free flowing reg or blown hose would be to shut down that post and breath from the reg on the operable post..... now if you blow a burst disk or the tank to valve o-ring (not the din or yoke o-ring) you would shut the isolator to preserve half of your breathing gas.

 

[MRTdiver]

Hi mahjong,

cavediving.com has a good diagram and explanation...
Manifold Operation

 

[mahjong]

Thanks Bix and MRT.

According to the diagram and explanation at cavediving.com, if there is a free flow/leak in (say) the primary 2nd stage, you close the right post/valve--presumably air stops leaking from the primary. This would suggest that air from the other tank is not traveling through the closed right valve and out the leaking primary. However, the explanation states that: "When one of the regulator valves is turned off (such as would be necessary in the case of a free flow), gas continues to flow from both tanks to the remaining regulator." (I'm assuming "regulator valve" means tank valve?) Air continues to flow from BOTH tanks? If so, this would suggest that, with the valve to the right/primary tank closed, gas from the other/left tank cannot enter through that closed right valve, but gas from the right/primary tank CAN leave through that closed right valve. Is this the case?

 

[techintime]

closing that valve (with a freeflowing component in the first stage or second stage) will prevent the loss of gas from either tank

 

[mahjong]

Thanks. And now breathing from the backup regulator, would the air from the primary/right tank (the tank whose valve we just closed) still be available to the backup regulator?

closing that valve (with a freeflowing component in the first stage or second stage) will prevent the loss of gas from either tank

 

[T. Bix]

Thanks. And now breathing from the backup regulator, would the air from the primary/right tank (the tank whose valve we just closed) still be available to the backup regulator?

Yes.... Don't overthink it! The isolator only "Isolates" the tanks from each other. The posts control only the first stages attached to them. If you don't close the isolator and switch regulators for a failure or "S" drill you will have access to all of your breathing gas. There are only a few reasons to touch the isolator one is during valve drills and the other that comes to mind is a blown/leaking burst disk in which case you'd need to isolate your tanks to preserve half of your breathing gas. You'd only have access to breathing gas from the tank and regulator that is obviously on the tank without the blown disk.

 

[mahjong]

Thanks Bix.

Good to have it clear. I still don't understand how a closed tank valve/post can allow air to flow out through the manifold, while not allowing air to flow in from the manifold? But I'll take your word for it.

Yes.... Don't overthink it! The isolator only "Isolates" the tanks from each other. The posts control only the first stages attached to them. If you don't close the isolator and switch regulators for a failure or "S" drill you will have access to all of your breathing gas. There are only a few reasons to touch the isolator one is during valve drills and the other that comes to mind is a blown/leaking burst disk in which case you'd need to isolate your tanks to preserve half of your breathing gas. You'd only have access to breathing gas from the tank and regulator that is obviously on the tank without the blown disk.

 

[Akimbo]

Attached is a schematic diagram for those who are more inclined to understand them. The objective is you can save about half or more of your remaining gas for any single failure. For example:

• Leak anywhere past the post/regulator valve seat including the regulator and valve stem itself: Close post valve for offending regulator/valve, isolation can be open.
• Cylinder O-ring, burst disk, or isolation valve O-ring(s) connecting post/regulator valves; leak or catastrophic failure: Close isolation valve and use regulator on the good side of the isolation valve. Closing a post/regulator valve serves no purpose.

 

[Thalassamania]

There are three valves, each with a separate and independent function. If we keep the isolator valve closed, then each "tank" valve (or "regulator" valve, or "post" if you will) controls just the flow to the regulator that is mounted on that valve (post). If you shut a post, gas stops flowing to that regulator. The isolator valve just interconnects the two cylinder. If the isolator valve is open you have one big gas supply, that can be accessed by either regulator assuming that the regulator's post is open. If it is closed you have two separate gas supplies, each only accessible by one or the other regulator, again, assuming that the regulator's post is open.