Reaching Valves - Performing shutdowns

[MarkP]

Originally Posted by Foggy

Ahh but can you do it at 40mtrs without crushing your vitals???Paul

I thought they always collapsed when their contents were sucked out.

[Brian of Aquanauts]

Originally Posted by Mark Chase

Well one ATM puts a presure on the hose of 14.7lb per square inch

At 6m its 23.5lb /inch/2

so at 60m the hose is under 102.9 lb per square inch. Which should be enough to flatten most things.


The argumnet is that the suposedly ambient gas inside the hose is therefore at a presure of 102.9lb to maintain ambience. You suck on the end of the hose and you will reduce the presure from ambient even fractionaly and equilibrium will be saught and the gas will flow into your mouth.

The los of volume of the gas will be taken up by the crushing of the hose.

I cant see how this is avoidable.


In the scinario of the valve leaking at the surface. The gas is at ambient at 6m and both the first and second stage are off so as the diver decends there is no balance of presure from the tank and no loss of gas via the second stage but the hose crushes anyway as the presure in the hose is below that of the outside presure.

Two totaly diferent ways for a hose to crush.

ATB

Mark

Mark ???? Come on... you must know this stuff.

If you're at depth, it is impossible to breath the reg down to anything less than a fraction below ambient (Which is the ambient pressure at the depth where you are).

For example, at 60m you could breath the hose down to 7 bar, to get it any less than a tiny fraction below this from a very forced suck (which would really hurt your mouth) would require a waterproof vacuum pump.

If the valve was shut and you descended then that is a different matter, and it would have the gas in it from whatever depth it was closed. As you descend the ambient pressure will crush the hose until the gas inside equals ambient pressure (as the gas becomes more dense).

Hope that helped.

Brian

[MarkP]

Originally Posted by Brian of Aquanauts

If you're at depth, it is impossible to breath the reg down to anything less than a fraction below ambient (Which is the ambient pressure at the depth where you are).

I refer the honourable gentleman to post 54 in this thread.

Beat you to it. Nah, nah, na-nah, nah!