1_T_Submariner
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Very interesting Info. Thanks for starting the thread.
Why two stages?
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Just a nit, but isn't the intermediate pressure coming out of an LP port more like 130-140psi?
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Let's keep the horse before the cart. Two stage regulators, single and double hose, existed long before BC inflators, dry suit inflators, auxiliary second stages, etc. All these devices came about because intermediate pressure was available, intermediate pressure was not invented to make these devices possible.
In a nutshell two stage regulators exist because it is far easier to precisely turn an intermediate pressure stream of air on and off than it is a high pressure stream. You could do even better with a three or four or five stage regulator but the gain would not be worth the pain.
In a nutshell two stage regulators exist because it is far easier to precisely turn an intermediate pressure stream of air on and off than it is a high pressure stream. You could do even better with a three or four or five stage regulator but the gain would not be worth the pain.
mike_s
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Intermediate pressure specifications are quite variable. The lowest I know of is the second stage in the Aquadyne hat (Mark 1 - Mod 0) at 60 psi over ambient and the highest I know is the Poseidon Cyclon 300 at 190 PSI over ambient.
oxyhacker
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Spare Airs are single stage, best I can recall. The use a compound valve system to operate a upstream poppet, actually very similar to the old Mistrals, reducing pressure from tank to ambient in one step. Who cares about cracking pressure? If you need air badly enough, you'll pull howeve hard it takes to get it!
No way one could make a single hose single stage. Cousteau and Gagnan tried to, with the prototype Aqualung, but it didn't work. It was a standard double-hoser only without the return hose, and predictably, freeflowed terribly until the return hose was added.
And someone - Demone? - made a two hose single-hose-style two stage. Basically two single hosers combined, so you had two demand valves in a single mouthpiece/2nd stage and one hose going around to the 1st on each side of the head (it also had corrugated exhaust hoses over the small intermediate pressure hoses, just to confuse things!). This was supposed to double the air supply but was almost useless as there was no way to tune it so perfectly that both demand valves would open at the same time, so one ended up doing all the work.
It's easy to forget now that you can drop $1000 on a new single hose reg, but one of the main reasons for coming out with them was economy - they could be manufactured much more cheaply that a double hoser. They were also a little easier to teach beginners on since they were easier to clear. The idea was originally that any serious diver would move up to a double-hoser, and most of the early single hosers were terribly cheap devices. Then, as their advantages began to make themselves known, and better ones appeared, they took over.
Oh lowest IP is probably Stig Insulins Sitech "Forever" Reg, generally considered the ultimate cold water reg. IP is only 50-70 psi or so.
No way one could make a single hose single stage. Cousteau and Gagnan tried to, with the prototype Aqualung, but it didn't work. It was a standard double-hoser only without the return hose, and predictably, freeflowed terribly until the return hose was added.
And someone - Demone? - made a two hose single-hose-style two stage. Basically two single hosers combined, so you had two demand valves in a single mouthpiece/2nd stage and one hose going around to the 1st on each side of the head (it also had corrugated exhaust hoses over the small intermediate pressure hoses, just to confuse things!). This was supposed to double the air supply but was almost useless as there was no way to tune it so perfectly that both demand valves would open at the same time, so one ended up doing all the work.
It's easy to forget now that you can drop $1000 on a new single hose reg, but one of the main reasons for coming out with them was economy - they could be manufactured much more cheaply that a double hoser. They were also a little easier to teach beginners on since they were easier to clear. The idea was originally that any serious diver would move up to a double-hoser, and most of the early single hosers were terribly cheap devices. Then, as their advantages began to make themselves known, and better ones appeared, they took over.
Oh lowest IP is probably Stig Insulins Sitech "Forever" Reg, generally considered the ultimate cold water reg. IP is only 50-70 psi or so.
Thanks for the info on the Spare Air, I have never taken mine apart before getting rid of it. A shop in Tampa made me buy one before they would take me to the Middle Grounds! It looked like it had two stages but if you say so, that is good enough for me. I don't think I would really car for HP air being that close to my lungs with out the springy hoses and "bypass" capability built into a real single stage double hose.
JFYI--WARNING---WARNING--DANGER--never ever ever breath directly from the horn on a double hose regulator, especially a single stage Mistral, it just might kill you.
The venturi tube on the Mistral shoots air right into the horn and remember, that woosh, woosh that a Mistral makes when you breath is HP air being regulated by a compound lever and entering the can via a venturi tube similar to what you see on old fashioned air nozzles in a garage and it is directed directly into the horn.The Demone was a strange and not very successful hybrid, sort of like a missing link in the evolutionary movement from double to single hose, a dead end. Occasionally they pop up on ebay but I have never been motivated to spend the dollars for something that never really worked well to begin with.
N
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 wasnt 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.
It's true the Mistal is an unbalanced diaphragm design that will breathe easier as tank pressure falls. But that has more to do with being an unbalanced diaphragm design than due to being single stage. You get the same effect with an unbalanced single hose/two stage regulator as the seat carrier is located upstream of the orifice. In an unbalanced piston reg you get the reverse effect (breathes harder as tank pressure drops) as the seat is located on the downstream side of the orifice.
In either case with a balanced second stage the effect of an unbalaced first stage can be virtually eliminated, and conversely with a balanced first stage producing a stable IP, the benefits of a balanced second stage are greatly reduced.
I agree however that adding a second stage increases the number of design options and makes creating a "balanced" reg much easier.
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