Spare Air on deep but no deco dives??

[doctormike]

This looks like a great set-up, but frankly I can't see traveling with and packing that, especially since I am able with my current set of equipment to do a 5-day (warm water/weather) trip with carry-on only luggage.

Another option is that many dive resorts have pony bottles for rent. If there are any tech divers there, they are used as deco bottles. Of course then you would probably be using an AL40.

 

[wetb4igetinthewater]

EWe are talking about safe diving practices. The fact that many divers think that this is a safe diving practice doesn't carry much weight in that discussion.

^^^^ THIS!!!!!

 

[scubadada]

Nothing like a good old Spare Air thread to get SB going

 

[ReadyDiverOne]

Nothing like a good old Spare Air thread to get SB going

Yeah man

 

[BDSC]

Nothing like a good old Spare Air thread to get SB going

Yep. Same old tired comments by those who want to let us all know that a 19cf pony has more air than the 3cf Spare Air. Brilliant!

 

[johndiver999]

Time to work the numbers. 100 ft is 4 atm. A unstressed breathing rate is typically 0.7 cuft.min; stressed will double or triple. The Spare Air has 3 cuft, not all of which is available (you can't breath a tank down below the regulator's intermediate pressure). So, how long will the Spare Air last at 100 ft while one is sorting out or looking for a buddy?

The whole discussion reminds me of the guy who was arguing how many jumps it would take to get across the chasm. The argument that a few extra breaths is better than none is like trying to jump the chasm in several jumps.

Can you explain more about the idea that a regulator does not work below the intermediate pressure? I'm not sure I understand what you mean?

 

[rsingler]

Can you explain more about the idea that a regulator does not work below the intermediate pressure?

An unbalanced second stage regulator is basically like a flap held closed by a spring. The force that opens the flap held closed by the spring is a combination of you sucking with a breath plus the intermediate pressure of the first stage, which is trying to push the flap open.

The lower the intermediate pressure, the less force there is opposing that spring , so you have to suck harder to open the flap.

Tank pressures higher than intermediate pressure don't matter to the second stage. The first stage regulates tank pressure down to intermediate pressure, which stays fairly constant as the tank empties (with some exceptions).

As tank pressure gets lower than the intermediate pressure, the valve opening "assist" supplied by the first stage gets less and less until, at some point, the valve won't open despite all the suck you can generate, due to the spring pressure.

A balanced second stage works much better. They often don't show signs of hard breathing until the intermediate pressure has dropped from 130 PSI to 50 psi.

But either way, you can't use the last fifty to one hundred or so psi in an empty tank.

 

[A.S.H.]

Hello,

Carry a spare tank, 19, 30 or 40 it's really up to you and the depth your planning to do.
I carry a 30, that's good for me to 130 ft.

A good pony (al19) and average 1st stage and 2nd, botton gauge, rigging, will cost as much as that spare air and be much more versatile.

 

[Tom N.]

I'll be brief. CESA only reliable for about 30 feet. Buddies are inherently unreliable. They are not looking at you all the time, so on a deep dive you might waste time and air chasing them to get their attention. Then what if they panic or think you are panicking , or for whatever reason don't provide the help you need ? You watch your gauge, but what if you blow a hose or an o-ring ? Bottom line , best to have a pony with high quality separate reg with enough gas to get you safely to the surface without help.

 

[wetb4igetinthewater]

An unbalanced second stage regulator is basically a flap held closed by a spring. The force that opens the flap held closed by the spring is a combination of you sucking with a breath plus the intermediate pressure of the first stage, which is trying to push the flap open.

The lower the intermediate pressure, the less force there is opposing that spring , so you have to suck harder to open the flap.

Tank pressures higher than intermediate pressure don't matter to the second stage. The first stage regulates tank pressure down to intermediate pressure, which stays fairly constant as the tank empties (with some exceptions).

As tank pressure gets lower than the intermediate pressure, the valve opening "assist" supplied by the first stage gets less and less until, at some point, the valve won't open despite all the suck you can generate, due to the spring pressure.

A balanced second stage works much better. They often don't show signs of hard breathing until the intermediate pressure has dropped from 130 PSI to 50 psi.

But either way, you can't use the last fifty to one hundred or so psi in an empty tank.

@LandonL

Care to chime in?