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

[BlueTrin]

This is a somewhat off topic newbie question, but how is the pressure to the SPG, or to a shorty hose connected transmitter, released after a day of diving? It's obvious how to release the wing and the regulator hose pressure. How is HP air hose pressure released?

It is connected to the first stage (to the high pressure chamber)

When the pressure drops and when you close the cylinder valve and purge before to disconnect, then it will drop.

It is by definition at the same pressure than the first stage (high pressure chamber). If it wasn’t then it would not be able to measure the cylinder pressure when the valve is opened?

 

[tursiops]

Also a longhouse should be less likely to freeze up because the hose stores more LP air,

Can you explain the physics of this?

 

[Gone for diving]

Can you explain the physics of this?

If I turn on my RH post, then shut it off with no pressure gauge hooked up,
And only 1 bcd hose, I have one extremely large lung full off air,
That lung full sits there stored ready for my next breath, warming up from the surrounding water. The first stage pressure drop makes the air extremely cold,
With a short hose no other hoses hooked up, most of the air is coming through the first stage, and will be colder air and be more likely to freeze at the second stage seat, because of another pressure drop,
Some point I think there was a debate that a long hose decreased second stage performance, don't know if it's still a thing, but a long hose acts as a reservoir,
And should make a second stage breath the same or better,
My long hose is 3/8 ID,

FYI double hose regulators are known to be nicer for ice diving, but I think it's because the exhaust warms the can and the inhale hose warms the air,

 

[tursiops]

If I turn on my RH post, then shut it off with no pressure gauge hooked up,
And only 1 bcd hose, I have one extremely large lung full off air,
That lung full sits there stored ready for my next breath, warming up from the surrounding water. The first stage pressure drop makes the air extremely cold,
With a short hose no other hoses hooked up, most of the air is coming through the first stage, and will be colder air and be more likely to freeze at the second stage seat, because of another pressure drop,
Some point I think there was a debate that a long hose decreased second stage performance, don't know if it's still a thing, but a long hose acts as a reservoir,
And should make a second stage breath the same or better,
My long hose is 3/8 ID,

FYI double hose regulators are known to be nicer for ice diving, but I think it's because the exhaust warms the can and the inhale hose warms the air,

OK, I understand the principle, but I doubt the significance. What is primarily missing is the very slow transfer of heat from the water to the air in the hose, through the thick rubber hose. What is also missing is that there is not that much air in the hose. I don't think you mean 3/8 ID; 1/4" would be more common. At 1/4 inch diameter, the volume of a 7 ft hose is about 0.0024 cuft or about 0.07 liters. When you take a really deep breath, your lungs hold about 6 liters. So when you turn the RH post back on and take a breath, you ar getting a LOT more air through the hose than was in it, so the dilution factor of maybe slight warmer air to a lot of very cold air is going to keep the air nearly as cold. And how long does it take for the heat to pass through the rubber hose and warm up the air? Rubber is a pretty good insulator....

Combine these two effects -- not much air in the hose to warm up, and not much warming up -- and I don't think it is worth hoping for.

Hey, I may have calculated something wrong... let me know!

 

[PfcAJ]

OK, I understand the principle, but I doubt the significance. What is primarily missing is the very slow transfer of heat from the water to the air in the hose, through the thick rubber hose. What is also missing is that there is not that much air in the hose. I don't think you mean 3/8 ID; 1/4" would be more common. At 1/4 inch diameter, the volume of a 7 ft hose is about 0.0024 cuft or about 0.07 liters. When you take a really deep breath, your lungs hold about 6 liters. So when you turn the RH post back on and take a breath, you ar getting a LOT more air through the hose than was in it, so the dilution factor of maybe slight warmer air to a lot of very cold air is going to keep the air nearly as cold. And how long does it take for the heat to pass through the rubber hose and warm up the air? Rubber is a pretty good insulator....

Combine these two effects -- not much air in the hose to warm up, and not much warming up -- and I don't think it is worth hoping for.

Hey, I may have calculated something wrong... let me know!

I think the missing variable is the IP.

IP would be like 140psi, or 9.5 atmospheres.

.07L x 9.5 atmospheres is 0.66L. Average tidal volume is 500mL. So there's a breath plus a bit in a long hose.

Right?

 

[Gone for diving]

At 1/4 inch diameter, the volume of a 7 ft hose is about 0.0024 cuft or about 0.07 liters.

Don't forget 150 psi =10.2 atm,
So basically .7liters,

Turning off the valve there is still hp in the DIN fitting plus the bcd hose, to add in my quick and dirt test,

I will grant it's not a huge difference,

Your right my normal rig is 1/4'' actually it measures .27'' ID and my hose length is 92" made it custom for me,

Mixed up my other long hose that's on a test design, which I better not show on scubaboard

https://www.google.com/url?sa=t&source=web&rct=j&url=https://divelab.com/download/procedures-and-guidelines/ScubaRegulatorFreezing-ChillingFacts-4-9-14.pdf&ved=2ahUKEwiVocS138b0AhXQGs0KHSboDlkQFnoECAMQAQ&usg=AOvVaw182pnMRCClrMjLYyGbFiCb

 

[elan]

I think the missing variable is the IP.

IP would be like 140psi, or 9.5 atmospheres.

.07L x 9.5 atmospheres is 0.66L. Average tidal volume is 500mL. So there's a breath plus a bit in a long hose.

Right?

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.

 

[crofrog]

@Kofferfisch
It's a pity that your club doesn't like it; seems like an old-school attitude (or they're avid cave divers).

why would cave divers be against long hose?

 

[Wibble]

why would cave divers be against long hose?

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.

 

[Wibble]

I think the missing variable is the IP.

IP would be like 140psi, or 9.5 atmospheres.

.07L x 9.5 atmospheres is 0.66L. Average tidal volume is 500mL. So there's a breath plus a bit in a long hose.

Right?

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.