Where should the pressure gauge be mounted and what are the advantages of this configuration?

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Wibble

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but it doesn’t?

Tidal volume is NOT the same as vital capacity….
A small breath still is x 5 at 40m/130ft.

A big breath will be 2.5 litres, so I guess I could re-do my calculations...
  • Surface: 0.7litres hose / 2.5 litres lungs = 28% of a full breath.
  • 40m/130ft/5ata: 1.05 litre hose / 12.5 litres lungs = 8.4% of a full breath.
 

PfcAJ

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A small breath still is x 5 at 40m/130ft.

A big breath will be 2.5 litres, so I guess I could re-do my calculations...
  • Surface: 0.7litres hose / 2.5 litres lungs = 28% of a full breath.
  • 40m/130ft/5ata: 1.05 litre hose / 12.5 litres lungs = 8.4% of a full breath.
Ok where are you getting 2.5 liters from?

That’s FIVE TIMES normal tidal volume.
 

tursiops

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Ok where are you getting 2.5 liters from?

That’s FIVE TIMES normal tidal volume.
But the "full lung" "big breath" is not a normal breath at tidal volume. It can be closer to vital capacity.
 

PfcAJ

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But the "full lung" "big breath" is not a normal breath at tidal volume. It can be closer to vital capacity.
Nah, look up reserve inspiratory volume. It’s like 2L.

If you exhaled ALL THE WAY (like uncomfortable coughing feeling kind of all the way) and took a huge forced breath, you’d maybe hit a volume of of like 5. SUPER uncomfortable, and not a thing people are doing.

It takes a few normal breaths to empty a long hose on the surface. Idk why this is magic to anyone. Go put your long hose reg on a tank and try it. It is known.
 

inquisit

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You can even test it. Pressurize your reg, turn it off, and breathe it down. It takes a breath or two to get the IP back down to ambient.

That may be true at the surface but not a 100 ft.
Why not? The density of air in lungs and hose increase by the same factor. I've not noticed a difference in breath-down while doing valve drills at 60 ft vs. 10 ft vs. 0 ft. which matches my expectation.
 

Wibble

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Why not? The density of air in lungs and hose increase by the same factor. I've not noticed a difference in breath-down while doing valve drills at 60 ft vs. 10 ft vs. 0 ft. which matches my expectation.
No.

The hose is pressurised to ambient pressure PLUS the intermediate pressure (approximately 10bar/ata). In the surface it’s 10 bar, at 40m/130ft it is 15bar/ata.

Your lungs are pressurised to ambient pressure, 1bar or 5bar in those examples.

Your breath is much larger than the hose capacity.
 

rjack321

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Depends where you cave dive.

Sump divers use short hoses to minimise the kit they need to carry through the dry chambers, possibly climbing or descending on ropes. Their diving is mostly solo even if caving together — there is no one to donate to.
Are you actually diving sumps? Cause I dive sumps and I still have a long hose - albit stuffed on the right hand cylinder in the quasi standard sidemount way. Sometimes I have a buddy sometimes I don't. I dont go changing my configuration just because I happen to be alone on a particular dive.
 

inquisit

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Your breath is much larger than the hose capacity.
My normal breath isn't (Tidal Volume), which is what I use most of the time while diving, including valve drills, as an example. Yes, I can drain it in one if I want to with a deep breath. My point was that depth does not change these outcomes.
 

BlueTrin

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Are you actually diving sumps? Cause I dive sumps and I still have a long hose - albit stuffed on the right hand cylinder in the quasi standard sidemount way. Sometimes I have a buddy sometimes I don't. I dont go changing my configuration just because I happen to be alone on a particular dive.
I think in the UK cave diving is mostly caving with less diving.
 

Wibble

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Are you actually diving sumps? Cause I dive sumps and I still have a long hose - albit stuffed on the right hand cylinder in the quasi standard sidemount way. Sometimes I have a buddy sometimes I don't. I dont go changing my configuration just because I happen to be alone on a particular dive.
Skirting around a difficult topic…. Sump divers are cave divers too...

Sump divers are frequently "cavers who dive" and only dive to get though a flooded sump to the next chamber. Their kit is minimalist as it needs to be caved through to the sump and beyond through subsequent sumps. They'll frequently be doing SRT (rope work) too. No-mount is common as are small cylinders, anything to keep the load light and compact.

Long hoses and the DIR configuration which originated and evolved in the Florida karst system but also proved useful for general purpose diving.

Other circumstances require different equipment and procedures especially where general purpose equipment won't work. Even sidemount has different styles. Sump divers use the right kit for the particular cave and sump they're working through.
 
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