Intermediate Pressure

[brittlestar]

Going back to regulator design, how was an IP range of approx. 125-145 psi chosen as the optimal range?

 

[michael-fisch]

No.
Michael

 

[tbone1004]

@brittlestar no, the IP is relative. The IP changes with depth so it is always ~135psi over ambient pressure. The first regulators were single-stage and turned tank pressure straight to ambient pressure in the mouthpiece. Then the 2-stage double hoses came out. How they settled on that IP I don't know, but it is a balance of spring pressures, diaphragm sizes etc. and not all regulators use 125-145. The first single hose regulator use/still uses ~165psi for it's IP for example

 

[buddhasummer]

Going back to regulator design, how was an IP range of approx. 125-145 psi chosen as the optimal range?

Michaels reply looks odd now. FWIW I think you should have left your post unedited, it's questions like that that people learn from. Cheers.

 

[Bob DBF]

Probably a function of the components of the second stage. A lot of old regulator design adapted technology and available parts from other uses.

In 1958 Sherwood adapted their piston gas regulator to be used underwater and made the design available to scuba companies. This was not altogether a mangnanamus gesture, as they were, at the time, the primary manufacturer of hp regulator parts and valves for the emerging scuba industry. Because of the common lineage of many regulators, a common IP would not be surprising.

Also there is a balance between a low pressure for ease of second stage operation and higher pressure to give enough volume of air flow to provide enough air at depth.


Of course I could be totally wrong.

Bob

 

[brittlestar]

I accidently erased my original post when editing it...sorry. What I asked was if the current range of approx. 125-145 IP above ambient pressure standard in modern regulators was decided upon because the recreational depth limit of about 130' or 5 ata comes to about 70psi. So at least IP 70 psi would be required to deliver air at 130' and that perhaps it was decided that double 75 psi to 150ish was a safe number. My thought process was after reading an article on constant mass flow:
Understanding Constant Mass Flow • ADVANCED DIVER MAGAZINE • By Paul Raymaekers
I know that the second stage takes the IP and changes it to ambient pressure. In the article cited it shows an example of descending with a regulator that DOES NOT compensate. When the IP is less than 2x the ata the regulator degrades in its ability to deliver air. That number was 330ft/10 ata/150 psi. This is what made me link that formula with today's standard IP's.

 

[tbone1004]

@brittlestar the CMF is pertinent to rebreathers where the ambient pressure chamber for the first stage has been blogged so it maintains a static IP. That is a very special use case and does not apply to any breathing gas regulators, only the O2 supply for CCR's. ALL open circuit first stages have an ambient chamber that is exposed to ambient pressure in some way shape or form and maintain a a constant IP relative to ambient pressure

 

[Luis H]

@brittlestar no, the IP is relative. The IP changes with depth so it is always ~135psi over ambient pressure. The first regulators were single-stage and turned tank pressure straight to ambient pressure in the mouthpiece. Then the 2-stage double hoses came out. How they settled on that IP I don't know, but it is a balance of spring pressures, diaphragm sizes etc. and not all regulators use 125-145. The first single hose regulator use/still uses ~165psi for it's IP for example

I hate to correct you, but not even close in the dive history.


The first single stage regulator came out around 1955, which is fairly late. The US Divers Over-pressure regulator. Which by the way, was the first regulator to incorporate a venturi flow assistance. It was designed by Emile Gagan working in Canada for Air Liquid (Spirotechnique). After the Over-Pressure came the Stream Air, the Jet Air, and finally (in 1958) the Mistral.

All the early double hose regulators were two stage. Starting with the very early prototypes from Gagnan during WWII. I think they were call the Gasone, but I am not sure. It was the automotive demand valve regulator that he adapted for breathing air.

The second demand valve regulator was a rectangular unit with also two stages. I can provide pictures if interested. No, I do not own one. There are very few in existence.

The first production (sold to the public) regulator was the CG45 (Cousteau Gagnan 1945). That regulator resembles all the later double hose regulators and it had two stages. The first stage did not have an adjustment screw like the later US Diver regulators did (Like the Warner Avenue, Aqua Lung Trademark units).

Also the first single hose regulator is not the one you are probably thinking about. The Posidon Cyklon came out around 1957. The Australian Porpoise single hose regulator came out around 1952.


Since the early two stage regulators (the WWII time period Gasone) were trying to use standard pneumatic parts, I am going to guess that the first stage was just set to the high end of a typical LP reducer regulator.

To this day my LP compressor puts out up to about 120 psi. So I am going to guess that the IP is just the high end of typical LP air.

Some of the early single hose regulators, like the Australian Porpoise and the first American made single hose regulator (the Rose Aviation regulator), both used what looked to be of the shelf pressure reducing first stages.

 

[Luis H]

I accidently erased my original post when editing it...sorry. What I asked was if the current range of approx. 125-145 IP above ambient pressure standard in modern regulators was decided upon because the recreational depth limit of about 130' or 5 ata comes to about 70psi. So at least IP 70 psi would be required to deliver air at 130' and that perhaps it was decided that double 75 psi to 150ish was a safe number. My thought process was after reading an article on constant mass flow:
Understanding Constant Mass Flow • ADVANCED DIVER MAGAZINE • By Paul Raymaekers
I know that the second stage takes the IP and changes it to ambient pressure. In the article cited it shows an example of descending with a regulator that DOES NOT compensate. When the IP is less than 2x the ata the regulator degrades in its ability to deliver air. That number was 330ft/10 ata/150 psi. This is what made me link that formula with today's standard IP's.

The "recreational depth limit" is a relatively new concept that just came out relatively recently in the history of diving. It has nothing to do with the history of diving equipment.

I don't think Emile Ganan gave the IP that much thought other than 125 to 145 psi just looks like the LP air in many industrial plants. So I am going to guess that the two are related.

The IP in open circuit demand regulators have always been depth compensated (unless you are talking about malfunctioning Sherwood with the dry-bleed, but that is a very recent regulator).

 

[tbone1004]

@Luis H thanks for the history lesson. I knew about the Porpoise but thought the Cyklon still had it beat by a few years, apparently not