Double hoses and trimix?

[knowone]

There is no pressure in the hoses and minimal air between cycles.

The pressure is in the tank and the air is in your lungs.

One end of the hoses is always available to be open if there is external pressure
so it is the structure of the hose that keeps its shape. There may be some water.

WHAT F****** PRESSURE. I ran out of bricks.

Get some thumb cuffs for your fingers.

The attractive assistant contortionist girl in the shiny tight costume is in a box under the table poking her finger through the umbrella hole in the middle.

Can you see it?

Very good.

 

[Double Diver]

Knowone what book is that? And please get that scanner working that's a great diagram.

 

[duckbill]

Knowone, no one was ever worried about the hoses collapsing. The corrugations are there to keep the hoses from kinking, while still retaining flexibility.

 

[Eric Sedletzky]

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.

Thank you now I understand. So theoretically the reg could be taken down to any depth imaginable (provided the diver could survive on whatever gas delivered) and the hoses will never collapse. The 1st stage IP will continue to sit right above ambient pressure that is inside the can because the pressure will push in on the diaphram holding a constant internal pressure of the pre set.
I could see the other problem with air at an extreme depth in that it becomes like syrup trying to breath it.
That was the point of the original question of running trimix through a DH. Helium being a very light and fast gas it must make a DH breath really nice when you're really deep.

 

[knowone]

What are all those words in posts 1 thru 6 and 19 duckbill.

I think D A. Aquamaster or Thalassamania or one of those, has a good scan.

I've been a bit busy looking for bricks.

LET'S GO DIVING published by U.S.DIVERS 60s.

Pretty much all you need to know about the stuff you need, how to use it
and then GO.

Before you get a copy of the U.S.N. Manual

Without having to mortgage your house or never own one because
you spent the deposit on all the unnecessary stuff recommended today.




But there is NEVER 135 pounds per square inch in the hose.

Syrup sounds right. The air oozes or rolls in rather than blows.

 

[duckbill]

What are all those words in posts 1 thru 6 and 19 duckbill........

But there is NEVER 135 pounds per square inch in the hose.

I meant no one who was involved in designing or manufacturing double hose regulators was ever worried about the hoses collapsing, so that is NOT why the hoses have corrugations.

The hoses will have at least 135 pounds per square inch in them anywhere deeper than 270 feet in sea water.

 

[John C. Ratliff]

What Captain described in Post #15 is the basis of the Cousteau-Gagnan patent for the Aqualung. But concerning the pressure in the hoses, what Duckbill is describing is that the ambient pressure at 270 feet of sea water is at least 135 psi. 270 feet divided by 33 feet per atmosphere is 8.18 atmospheres (gauge; it is actually 9.18 atmospheres absolute--with the atmosphere itself counted). If you then multiply that 9.18 atmospheres absolute by 14.7 psi per atmosphere, you get 134.946 psi absolute, or 135 psi absolute.

But, and this is significant, there is not 135 psi difference between the inside hose pressure and the outside ambient water pressure, as both sides of the hose experience approximately the same pressure. There is at most about 12 inches of water pressure difference due to positional differences between the mouthpiece and the LP diaphragm of the regulator. I was taught that there is a difference in water pressure for salt water (it's slightly less for fresh water) of 0.445 psig per vertical foot. So the difference between the ambient water pressure and the mouthpiece is probably at most 0.445 psig. Therefore, the greatest pressure which would be on a double hose regulator would most likely be about half a psi (0.5 psig). By the way, there is a slight difference between the exhaust mushroom of most single hose regulators and the center of the diaphragm, which in some positions can cause a single hose regulator to leak air if it is extremely well tuned--has less than about 3/4 inch breaking pressure.

The diagram in Let's Go Diving by Bill Barada is a little different, in that it shows the difference between the demand second stage diaphragm and the center of the lungs. This is how we as divers sense ease of breathing--the difference between the lung pressure and the regulator's LP diaphragm placement in the water column. This diagram is meant to show the difference between the single hose and the double hose for different positions. In a "normal" swimming position, the double hose regulator has "negative pressure, two hose--equals hard inhalation, easy exhalation." For a single hose regulator, "positive single-hose equals easy inhalation, hard exhalation." It was the hard exhalation which kept the single hose regulator from being accepted by the U.S. Navy for many years--not until the AMF Voit MR-12 came along did the U.S. Navy accept a single hose regulator; it had a larger exhaust than its competitors, and forced U.S. Divers to come up with a modified Conshelf and the third generation of the Calypso.

SeaRat

 

[duckbill]

But, and this is significant, there is not 135 psi difference between the inside hose pressure and the outside ambient water pressure, as both sides of the hose experience approximately the same pressure.

Exactly. Thankyou, John. That is what I was getting at. The hoses have no significant pressure differential between the inside and the outside, and the designers never expected that there would be.

 

[knowone]

I meant no one who was involved in designing or manufacturing double hose regulators was ever worried about the hoses collapsing, so that is NOT why the hoses have corrugations.

The hoses will have at least 135 pounds per square inch in them anywhere deeper than 270 feet in sea water.

So tell them, those that are theorising and not me.

So if you could put John C's formulae away and use your practical brain,
I'm still wondering of what these hoses will have in them that is 135psi,
when it takes a puff of breath at any depth to open the non return valves
despite the fact that even if sealed these hoses cannot handle that pressure?

 

[herman]

Thank you now I understand. So theoretically the reg could be taken down to any depth imaginable (provided the diver could survive on whatever gas delivered) and the hoses will never collapse. .................................

Nope, trick question. At a around 6000 ft the ambient pressure would equal that of a full (3000psi tank). That depth, the internal pressure and extrenal pressure of the tank are the same so no gas would flow into the reg and the hoses would start to collapse. If however, the reg was being supplied from a pressure source that was capable of keeping at least a few psi over ambient going into the reg then you are correct, the hoses would never collapse.

..................................The 1st stage IP will continue to sit right above ambient pressure that is inside the can because the pressure will push in on the diaphram holding a constant internal pressure of the pre set.

Not exactly, there are 2 diaphrams and pressures to deal with. The pressure in the cans will remain equal to the water pressure around it, the IP will remain at it's setpoint (usually around 135psi) + can pressure. As you decent, the second stage diaphram will flex to control pressure in the cans, keeping it equal to ambient pressure and the first stage diaphram will flex to keep the IP at it's setpoint above the can pressure (which is equal to ambient if all is going well).