Second stage pressure...

[scubajb]

What pressure does the second stage deliver air to the diver after being staged down from the tank? Just looking for general area i.e. 3000 psi down to breathing pressure and I know ambient pressure plays a big role??? Just wondering about delivery force from the tank through the first and second stages and the ballpark amount that is supplied when we actually take that breath...

My kid asked me this morning before his science project presentation? I could look it up but I'm lazy on this Friday morning!

jim

 

[SteveAD]

The first stage steps the pressure down from tank pressure ~3000+psi to intermediate pressure,
usually about 130 to 150 psi in the LP hoses. The second stage is designed as a demand valve which delivers at ambient pressure there is NO "delivery force" you do after all have to suck to get the air.

 

[Hank49]

Here's a pretty good description. Howstuffworks "Regulators and Scuba Breathing Apparatus"

 

[fppf]

cracking pressure is normally about 1 inch of water colume above ambient pressure.

 

[scubajb]

The air is under pressure to the second stage - that is released when "sucking down" and delivered at or around ambient pressure and that changes depending on depth. That's the question I guess, He was looking for a ballpark range that the kids will understand (tank filled from 2800 to 3000 pounds on the surface) and I normally breathe it at ? (range depending on depth)...

 

[Hank49]

The air isn't delivered through the second stage under pressure. You have to draw it through with resistance being caused by depressing the spring with the diaphram. Some regs are easier to breath than others due to design.
The volume of air you breath will remain the same at different depths but the density will double at 10 meters triple at 20, times 4 at 30 etc etc. due to the ambient pressure increase.

 

[fppf]

1 Atm is about 14.7 psi
Every 33 feet of water adds another Atm.

Your regulator will always crack at about 1 inch of water higher than ambient pressure.
The pressure from the first stage will always be about 150 PSI above ambient pressure.

 

[scubajb]

Exactly, I thought that is what I had said... It's Friday morning and I must be communicating as usual... what is the range of ambient pressure that would be "breathed in" or "delivered" at the second stage say from the surface to a depth of 40 feet - slightly over 2 bar... I'm not saying that when I take a breath that a high pressure volume of air blows into the mouth... I was just wondering a range that the ambient pressure would be at time of delivery - or as you say breathing in. I appreciate your patience...

 

[scubajb]

That's the number I was looking for... Thank all of you, I'm not the worlds best communicator!

1 Atm is about 14.7 psi
Every 33 feet of water adds another Atm.

Your regulator will always crack at about 1 inch of water higher than ambient pressure.
The pressure from the first stage will always be about 150 PSI above ambient pressure.

 

[redacted]

Ambient pressure plus or minus a tad. Some regulator may feel like they are forcing gas into you (freeflowing) as you breath. This is know as positive pressure breathing which some find uncomfortable. You can see here (http://www.oceanicworldwide.com/img/p_regulators_zeta_wob1.gif) where the inhalation cycle involves both positive and negative pressure about the zero (ambient) line.