Questions about pressure of regulator

[Dr. Lecter]

With a final stage at the diver's mouth the ambient pressure is measured at the diver's mouth (give or take and inch) and there is less work of breathing.

Not quite. The first stage is still doing the work of sensing ambient pressure, and delivering intermediate pressure at ambient + X psi. What's happening in closer proximity to the diver's air hole is cracking pressure, thereby lowering WOB.

 

[tbone1004]

dfx, you're right. I'm all sorts of mucked up today. The unbalanced is on the back side with tank pressure. this is why you don't post on little sleep after stressful work weeks with technical stuff.

 

[raftingtigger]

Originally Posted by raftingtigger
With a final stage at the diver's mouth the ambient pressure is AGAIN measured at the diver's mouth (give or take and inch) and there is less work of breathing.

Not quite. The first stage is still doing the work of sensing ambient pressure, and delivering intermediate pressure at ambient + X psi. What's happening in closer proximity to the diver's air hole is cracking pressure, thereby lowering WOB.

Guess I wasn't clear, see the addition above. Both the 1st stage AND the 2nd stage independently sense ambient pressure. Cracking pressure is essentially the amount of pressure below ambient (inside the 2nd stage case) that is needed to open the valve (in the 2nd stage) and deliver gas to the diver.

 

[Couv]

Great post in this thread so far. However, I call on my friend Luis H to provide a bit of "scuba regulator history" in order to set the record straight. The original Cousteau/Gagnon regulators were two stage models.

Actually the original Cousteau / Gagnan prototype regulator, the Gasone (sp?) was a two stage regulator, so was their first production rectangular bakelite regulator and probably their most important the CG45 (the first to have the same looks as most double hose introduced in 1945) was also a two stage regulator.

The Gasone originally did not have the exhaust hose and therefore it did free flow when the exhaust (at the mouthpiece) was higher than the demand valve diaphragm (mounted on the tank valve). The actual Cousteau Gagnan patent was related to the exhaust location and the exhaust duckbill.

The first single stage regulator was the Over-Pressure DX regulator also design by Gagnan and was introduced around 1955. The single stage regulators (first the Over Pressure DX, then the Stream Air DW, and then the Mistral DW) were the very first regulators to incorporate a venturi flow assist and therefore they actually breathed better than the two stage regulator of the time.

The early two stage regulators (such as the CG45, the original Aqua Lung, the Navy type DA, the Navy Approved DA, etc.) did not have any venturi flow assistance. My understanding is that the DA Aqua Master was the first two stage regulator to incorporate the venturi flow assistance (in 1958).


BTW the first stage in the Gasone looked just like an oxygen welding regulator and Gagnan just attached to it the demand valve second stage. It wasn’t until the CG45 that the two stages where integrated into the single housing we are familiar on vintage double hose.

It is kind of interesting that the latest double hose, the new Mistral actually looks more like the very early Cousteau/ Gagnan regulators and it also basically lacks any significant venturi assistance.

If you've enjoyed reading this thread as I have, you will very much enjoy reading the thread where I plucked the above post.

http://www.scubaboard.com/forums/regulators/236067-why-two-stages.html#post3596381

 

[captain]

There was a single stage regulator that was very much like a single hose. The US Divers DX Overpressure. It looked like a normal two hose regulator but had a smaller hose inside the the large corrugated hose that connected to a special mouthpiece with a diverter that directed the air from the small hose directly into the mouth.

http://vintagedoublehose.com/vdh-manuals/mistral.pdf

 

[DogDiver]

This issue was tried and used extensively in the 60's by the dive industry. They were called a two stage double hose regulator. And prior to that, a single stage double hose regulator. I took one of mine to Roatan a few years ago. Well..... It breathed just as bad at 100 feet as it did at 30 feet.

 

[NAM001]

With the one stage or 2 stage double hoses, the delivery pressure was referenced from behind you and at a shallower depth. Then the single hose arrived and the first and second stages were seperated. Now the hasmat part of the reg (first stage ) is only an inch or so in size, and the 10 bar (non hasmat) section is now present at the mouth where the breathing is done. Much smoother and eassier breathing, especially in horizontal trim. no more free flows when the reg comes out of your mouth. If ou get the chance some time try an old single stage double hose and roll on your back and notice the forced air delivery. 2 stage single hose fixed that.

I'm going to sound incredibly stupid, but I have wondered the same thing, about why this has to be done in two stages. Is weight really the only answer?