Double hoses and trimix?

[Paladin]

They also used double hoses with Heliox (notably on the HMHS Brittanic).

Yeah. The Navy used heliox as far back as 1939 to dive on the Squalus.

 

[captain]

The operation of any type regulator is the same, single or double hose and the compensation of the first and second stage is exactly the same. In the case of the first stage it automatically maintains IP at the IP set pressure, say 135 PSI above the surrounding ambient pressure. The second stage does exactly the same thing except it maintains pressure at exactly surrounding ambient pressure not above or below it.

 

[oldmossback]

The second stage does exactly the same thing except it maintains pressure at exactly surrounding ambient pressure not above or below it.

Captain, how does the 2nd stage on a USD/Voit/etc etc.......compensate for the 6-8 inches of water column between the can and mouth piece......granted it isn't much of a difference, but in the head down position one does notice the extra effort breathing, so is the ambient pressure at the mouthpiece less or the same in the head down position?

Single stage regs can do this as they are in the lower position.......but DHR's are not.....I suspect the through the hose concept can adjust for this with physics, but how does the common DHR?

 

[Paladin]

The pressure in the hoses matches whatever pressure is inside the can. If the mouthpiece is level with the can, then the pressure in the hoses, the pressure at the MP and the pressure in the can are all equal and breathing resistance is normal. If the MP is higher than the can (head up), then the pressure in the mouthpiece is slightly higher than the surrounding water pressure and breathing resistance is reduced. If the MP is lower than the can (head down) then the pressure in the hoses and at the MP is lower than the ambient pressure at the MP and breathing resistance is greater.

Whatever the the pressure is at regulator level, that's what you get at the mouthpiece. There is no compensation other than what the diver does by changing position.

Back when I was diving DH as a kid, I was taught to roll over on my back if I needed to rest and catch my breath after heavy exertion.

 

[captain]

The regulator only cares where the exhaust valve is in relation to the diaphragm and as the two are side by side the difference to the 2nd stage is nil. You notice a difference during inhalation and exhalation because of the difference in water pressure between your lungs and the diaphragm and exhalation valve. The DH inhales easier and exhales harder when the regulator diaphragm and exhalation valve is below the level of the lungs. The opposite occurs when the diaphragm and exhalation valve is above the level of the lungs.
Let compare it to a snorkel. You know that the longer and deeper the snorkel the harder it becomes to inhale because your lung have to act against a higher pressure than they do on the surface. It is virtually impossible to inhale from a snorkel at a depth of 3 feet The same thing would happen if the regulator was raised 3 feet above your lungs.

 

[knowone]

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[Paladin]

Nive visual, Knowone.

 

[knowone]

Pity I keep overheating computers and not reinstalling the scanner

 

[Eric Sedletzky]

OK,
so what happens when the depth pressure exceeds the pressure delivered by the 1st stage set at lets say 135 psi. Then do the hoses begin to collapse. And at what depth would that be.
I remember starting a thread a while back about the depth record for a double hose and 400 or 500 feet was mentioned. I can't remember if the diver came back alive but I take it the reg still worked at that depth. I think Captain figured it was a Navy Approved model?

Not that any of this really means anything, it's just that it's winter and we're all sitting here.

 

[duckbill]

OK,
so what happens when the depth pressure exceeds the pressure delivered by the 1st stage set at lets say 135 psi. Then do the hoses begin to collapse. And at what depth would that be.

That 135psi IP is 135psi above ambient pressure, whatever that happens to be at whatever depth. This is because the back side of the IP (1st stage) diaphragm is exposed to ambient pressure.