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

[inquis]

But...a 5 litre lungful on the surface is 25 litres at 40m/130ft/5ATA.

The IP is 140 psi over ambient, so there's also more in the hose at 40m.

 

[Wibble]

The IP is 140 psi over ambient, so there's also more in the hose at 40m.

OK.

Hose contains 0.07 litres on the surface, multiplied by the intermediate pressure of ~10bar/ata = 0.7 litres.
At 40m/130ft/5ata the hose contains intermediate pressure plus 5 bar ambient pressure, i.e. 10+5 = 15bar/ata, so 0.07 x 15 = 1.05 litres.

The lungs will do circa 5 litres as a deep breath at surface pressure.
That same deep breath at 40m/130ft/5ata the lungs will be 5 litres x 5 bar = 25 litres.

Ratios:
surface: 0.7litres hose / 5 litres lungs = 14% of a full breath.
40m/130ft/5ata: 1.05 litre hose / 25 litres lungs = 4.2% of a full breath.

 

[PfcAJ]

OK.

Hose contains 0.07 litres on the surface, multiplied by the intermediate pressure of ~10bar/ata = 0.7 litres.
At 40m/130ft/5ata the hose contains intermediate pressure plus 5 bar ambient pressure, i.e. 10+5 = 15bar/ata, so 0.07 x 15 = 1.05 litres.

The lungs will do circa 5 litres as a deep breath at surface pressure.
That same deep breath at 40m/130ft/5ata the lungs will be 5 litres x 5 bar = 25 litres.

Ratios:
surface: 0.7litres hose / 5 litres lungs = 14% of a full breath.
40m/130ft/5ata: 1.05 litre hose / 25 litres lungs = 4.2% of a full breath.

Vital capacity is not the same as tidal volume.

You aren’t moving 5L in a breath.

 

[tursiops]

Vital capacity is not the same as tidal volume.

You aren’t moving 5L in a breath.

I have one extremely large lung full off air,

This sounds more like Vital capacity than tidal volume.....he is not talking about just taking a breath.

Exactly, thats pretty apparent for those who practice valve drills. It takes a couple of shallow breaths to breathe the hose dry after shutting down the post.

Also not what Rol diy is talking about; "large lung full of air" is not the same as "a couple of shallow breaths." In any case, valve drills are done near the surface, so the ATA is approx 1.

But...a 5 litre lungful on the surface is 25 litres at 40m/130ft/5ATA.

Not enough for a deep breath in a long hose, although just enough for a shallow breath to let you realise the valve's switched off.

Exactly.

 

[Wibble]

Point is that there’s not much gas in a hose, certainly nowhere near enough for a lungful

 

[PfcAJ]

Point is that there’s not much gas in a hose, certainly nowhere near enough for a lungful

But… there is? We just calculated it…. Your lungs are never completely empty. And you never top out their capacity during a normal breath. The tidal volume is less than what’s in the hose when you factor in the increased pressure inside the hose.

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.

 

[grf88]

But… there is? We just calculated it…. Your lungs are never completely empty. And you never top out their capacity during a normal breath. The tidal volume is less than what’s in the hose when you factor in the increased pressure inside the hose.

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.

 

[grf88]

The IP is 140 psi over ambient, so there's also more in the hose at 40m.

At 100 ft. the pressure in the hose will increase about 30% but air requirement will increase by a factor of about 4.

 

[Wibble]

But… there is? We just calculated it…. Your lungs are never completely empty. And you never top out their capacity during a normal breath. The tidal volume is less than what’s in the hose when you factor in the increased pressure inside the hose.

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.

One full breath will empty the hose on the surface. It will be less than that at depth.

Anyway, how did we get here... I'm lost!

 

[PfcAJ]

One full breath will empty the hose on the surface. It will be less than that at depth.

Anyway, how did we get here... I'm lost!

but it doesn’t?

Tidal volume is NOT the same as vital capacity….