Double hoses and trimix?

[Eric Sedletzky]

How many of you have run any sort mixture of trimix though your double hose.
Did you find that the gas made the reg perform any different or better than plain air?

Has anybody here used a heavy mixture of tri for a really deep dive with a double hose, let's say 250 to 300 feet?

And how come the hoses on DH regs don't collapse under deep water pressure?

It's winter and I'm bored, so that's why the topics.

 

[Paladin]

How many of you have run any sort mixture of trimix though your double hose.
Did you find that the gas made the reg perform any different or better than plain air?

Has anybody here used a heavy mixture of tri for a really deep dive with a double hose, let's say 250 to 300 feet?

And how come the hoses on DH regs don't collapse under deep water pressure?

It's winter and I'm bored, so that's why the topics.

Cousteau's crew used to dive that deep with double hose regs on air.

The hoses don't collapse because the pressure in the hoses match the water pressure. Think about it.

 

[Gombessa]

The hoses don't collapse because the pressure in the hoses match the water pressure. Think about it.

That's what I would think; the physical ribbing of the hoses isn't what's preventing them from collapsing even at recreational depths. As long as the regulator is capable of moving the volume of compressed air at the given depth required to replace the amount you inspire, the hoses don't collapse.

A somewhat-related question, and from a completely vintage-ignorant perspective, I'm guessing if you never take a breath from the reg while dropping from the surface, the increasing pressure from the water would start to work on the inlet side of the hose until the cracking pressure from the diaphragm is reached and it opens to equalize?

 

[Paladin]

That's what I would think; the physical ribbing of the hoses isn't what's preventing them from collapsing even at recreational depths. As long as the regulator is capable of moving the volume of compressed air at the given depth required to replace the amount you inspire, the hoses don't collapse.

A somewhat-related question, and from a completely vintage-ignorant perspective, I'm guessing if you never take a breath from the reg while dropping from the surface, the increasing pressure from the water would start to work on the inlet side of the hose until the cracking pressure from the diaphragm is reached and it opens to equalize?[/QUOTE]

Actually, as you descend, the water pressure acts upon the big diaphragm in the regulator housing and pushes it in, opening the valves until the air pressure in the regulator housing and hoses matches the ambient water pressure.

 

[Gombessa]

Actually, as you descend, the water pressure acts upon the big diaphragm in the regulator housing and pushes it in, opening the valves until the air pressure in the regulator housing and hoses matches the ambient water pressure.

Ah. Sorry, I think that's (almost?) what I was trying to get at: increasing pressure opens the diaphragm to equalize pressure before the hose shows any physical signs of compression.

 

[Paladin]

Ah. Sorry, I think that's (almost?) what I was trying to get at: increasing pressure opens the diaphragm to equalize pressure before the hose shows any physical signs of compression.

Yup.

 

[knowone]

My take is that ambient acting on the diaphragm(s) is there for assistance.
If water pressure acted to release tank air without inhalation, this would
create a constant flow system constantly flowing past the one way button
valves in the mouthpiece bypassing the lungs and out the valve in the can.

The pressure in the hoses is only ever as much, less, as in a second stage of a
single hose reg when inhaling and exhaling. The 100 plus psi or whatever it is
is held in and released from the metal box hooked to the tank behind your head.

When you take the mouthpiece out and start a freeflow, there is no pressure
in the inhalation hose just flowing air and if the pressure on the exhalation
hose were so great, the air would be squeezed out the valve in the can.

I think problems with oxygen rich mixtures occur in the tank valve from
grease or quick cracking and not from rubber or titanium or unobtanium.

My favorite reg has parts of neoprene nitrile silicone with an epdm diaphragm,
I think and has been down to nitrox depths with nitrox and deep with air.

I have no idea about performance differences and depths and can't remember.

It's a very good Drager double hose reg and it does double hose reg things.

Breathes good, whatever that means. :scubadive:

 

[herman]

Off hand I don't see any reason trimix could not be used. I am not a techie but if I remember PO2s right, the percentage of O2 in deep mixes is less which would make any kind of reaction problem less. I know for fact some DH regs see a lot of nitrox, mine has had hundreds of tank through it. The 2 stage regs (DA'a andRAMs) are for all intents and purposes the same internally as a modern reg, just packaged different. The one thing that does come to mind is air density at very deep depths. Since you have to move the air farther and through the hoses, considerably denser air might make WOB higher.

The pressure in the hoses never gets more than a little below ambient. As you decend the increasing ambient pressure will push the diaphram in, starting air flow and equalizing the internal pressure.

 

[Gilldiver]

I have run mix a few times, mostly 21/30 or 21/35. The major problem is lack of back gas tank size as all of my large tanks have DIN tank mounted valves, which pulls the cans to one side so you need a hose set with two lengths, so I have to run my 72's which is not enough for me past 140 or so. The other problem is parking the mouth piece out of the way for using any deco gasses in such a way as not to get freeflows.

Louis has a mouth piece design that should work to close off the mouth piece for deco parking but I haven't seen Bryan bring it out yet.

 

[Rhone Man]

Cousteau's crew used to dive that deep with double hose regs on air.

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