Why two stages?

[oxyhacker]

Intersting, that they went from a two stage to a single stage.

There was one other candidate for single-hose single stage, the Normalair, which had just a valve on the tank, and a high pressure hose going to the tilt valve regulator on the full face mask.

Early single hosers often showed their industrial roots in their 1st stages. The Rose and the Northhill, for example, look as if their first stages came straight out of an industrial supply catalog.

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.

 

[Luis H]

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.

I agree, but I would like to expand a bit.

The Mistral DW (also the Over-Pressure DX, then Stream Air DW, and several others) used a single stage upstream unbalanced demand valve. But, there was at least one regulator (it was made by Voit) that used a single stage down stream demand valve. I can’t remember the model, maybe Captain can add to this.

As expected the down stream single stage demand valve regulator breathes easier with a full tank and gets harder towards the end of the dive.

An interesting side note, that upstream single stage demand valve regulator was the only design from Emile Gagnan that was only produced by Voit and US Divers never made a version of it.

There was also at least one attempt at making a balanced single stage demand valve. I am referring at the US Divers Royal Mistral (I don’t believe any of the Spirotechnique Royal Mistrals were ever balanced). The concept of a balanced single stage regulator is very interesting and perhaps it could have been very promising, but the implementation in the USD Royal Mistral was in my understanding a failure. They were only around for maybe two years and my understanding is that they all leak. US Divers used a unique cone seat in that regulator.


Unbalanced diaphragm or unbalanced piston first stage is not really the determining factor whether the IP rises or drops with tank pressure. The important factor is if the valve motion is upstream or down stream. We always think of unbalanced piston as down stream and unbalanced diaphragm as upstream, but that is just a design coincidence since it has been convenient to design it that way…and most designs are just copies of previous design (you could almost say that most regulators are just modified copies of Emile Gagnan designs…the only exception may be the use of a the piston).

It is very possible to design a diaphragm or piston first stage with a reversed motion valve, but what would be the point?

 

[Nemrod]

And it would be possible to design a single hose and single stage but again, why would anyone do it? The mechanism would be contained fully in the mouthpiece section, a HP hose would deliever the air. The housing would be rather large I imagine and some elasticity would have to be provided in the system to prevent embolisms as would ocurr if breathing directly fromthe horn on a Mistral.

N

 

[Luis H]

Intersting, that they went from a two stage to a single stage.

There was one other candidate for single-hose single stage, the Normalair, which had just a valve on the tank, and a high pressure hose going to the tilt valve regulator on the full face mask.

Early single hosers often showed their industrial roots in their 1st stages. The Rose and the Northhill, for example, look as if their first stages came straight out of an industrial supply catalog.

Yes, it is very interesting that most single stage regulators didn’t show up until a few years after the introduction of the CG45 (name stood for Cousteau / Gagnan 1945).


If you are looking for single stage single hose... well how about the Dräger Delphin II.
Here are some pictures from: Delphin II

You can see that it exhaled into the same inhalation hose.
Some Specs:

Manufacturer: Dräger
Name: Delphin II
gebaut / built: 1951 - 1966
max. Luftlieferleistung / max.air delivery: no Information by now
Stages: 1
Stage 1: Upstream
Balanced?: no
Type: membrangesteuert / Diaphragm activated
Mitteldruck / IP: keiner / none
HP-Port: no
Stage 2: no
LP-Port: no
Gehäuse/Housing: Metal
Membrane Ø / Diaphragm: Ø 12 cm
max Druck / Pressure: 200 bar / 3500 psi
Anschluss/Fitting: DIN


See his full web site for many interesting regulators:
Scubacollector

 

[pescador775]

The Northhill was a two hose, single stage regulator produced in the 1950's. The mechanism appears to be balanced. According to my interpretation, the comprensatory mechanism is the floating valve seat which increased or decreased the leverage in accordance with the supply pressure. In the 1960's a balanced version of the single stage, Mistral double hose was offered by US Divers. This was done using the engineering principle often described as balanced poppet design.

In the 1950's, few people were able to afford a diving set so the single hose regulator and the single stage regulator were designed as entry level, cheaper to purchase products. I think that this has been mentioned. Although the original single hose was of the theoretically expensive, two stage design, it encorporated existing hardware for the first stage which was already being sold in volume for other purposes. The second stages used very simple, plastic components, also cheaper to produce than the expensive, chrome castings of the double hose, single or double stage.

The two stage, two hose, Aquamaster regulator was first produced in 1958, I think, and incorporated a low pressure fitting (1/4 inch oxygen nut). This was supposed to be used for various purposes, surface supplied air and pneumatic tools. In practice, nobody used them and other two hose mfgrs did not install LP ports for a long time. The BCD had not yet been invented although life jackets were used, rarely. The concept of buoyancy control by injecting air into the BCD was unknown. Things changed when BCD's, dry suits, lift bags, octopus regs and other stuff began to sell.

When these products surfaced (so to speak) in the 1970's, a cottage industry grew up supplying adapters for single hose, first stages. These allowed multiple take off ports for LP air hoses. Later, the regulator designs incorporated these ports eliminating the need for adapters. This is what Thallasamania was talking about. So, generally, the LP port appeared very early but nobody knew what to do with it, not for almost 15 years.

 

[Thalassamania]

Was there not, at one time, a three stage double hose? I seem to recall something about that from my childhood.

 

[Luis H]

Was there not, at one time, a three stage double hose? I seem to recall something about that from my childhood.

The Nemrod Snark II and Snark II Silver (and maybe others) were advertised as a three stage regulators, but the third stage was just a relieve valve. The demand valve in the second stage were upstream needle style valve which required the overpressure relive valve.

 

[captain]

I think that you may be thinking of a Dacor R4 duel diaphragm regulator that was sometimes referred to as 3 stage but actually was 2 stage.

 

[Thalassamania]

The Nemrod Snark II and Snark II Silver (and maybe others) were advertised as a three stage regulators, but the third stage was just a relieve valve. The demand valve in the second stage were upstream needle style valve which required the overpressure relive valve.

I know the Snark, I've got one kicking about ... but that's a single hose.

I think that you may be thinking of a Dacor R4 duel diaphragm regulator that was sometimes referred to as 3 stage but actually was 2 stage.

Was that a double hose made in the late 50s early 60s? My memory (and we all know that's the first thing to go) is of a rather conventional looking two hose reg that someone said (who knows what that someone actually knew ... I was a kid and was brought up to believe adults - STUPID!) was three stage.

 

[vicdiver656]

I've been diving for about a year now, and right now I am try to get a deeper understanding how my equipment works.

I've been researching regulators, and I have a decent grasp on how they work, but one thing has always escaped me...why two stages?

I know a SpareAir type systems use a single stage, so it is not impossible to do. Why are two stages better? I have some guesses, but I am not sure:

• Safety - two points of failure between your lungs and 3000 psi
• Engineering - two smaller pressure drops might be easier to engineer than one big one
• Flexibility - both divers and manufacturers can mix and match stages for their own purposes
• Reliability - a single stage is ok for a rescue bottle, but will not hold up to regular use
• Performance - you just can't get easy breathing across different depths from a single stage

All of these sound somewhat plausible, but I have not been able to find much to back them up.

Any ideas?

Why two stages? Here's a simple answer. Ever tried breathing air at 3000 PSI? It's impossible, and don't try it. It is estimated that an AL80 filled to 3000 PSI has enough pressure to lift a US destroyer 3 feet out the water if an inflatible bag was placed under it. There is one stage to reduce 3000 PSI down to 450 PSI (is that right techies? I'm not quite sure) and then another to reduce 450 PSI down to ambient, or breatheable pressure. As to the engineering, if you were to have one big pressure drop, the size of the regulator in your mouth would be huge, as materials would have to be reinforced to sustain pressure. The flexibility? Many divers mix and match their regs, choosing different performance regs according to their preferences. The cost also places a larger factor. What if one reg breaks, you would have to buy another whole new reg system to replace it....too expensive. The reliability? Most spare air or rescue bottles only provide a few breaths, and are not designed to be breathed on for a long time. The pressure in the bottles is not high enough to require a second stage to drop pressure. The performance? I think you are partly right there. Air shrinks at depth, and all regs breath harder as you get deeper. If you were to have a single stage, I think that the change in breathability would be dramatic, and almost impossible to adapt to.

Saying this, I am no expert. I also have been diving for a year. My teacher just took the time to instruct me on exactly how regulators work! My comments definitely will not be the best. You might look at articles by DA Aquamaster. He is a reg technician, and very informative.

Hope that helps,
Taylor
Vicdiver656