Why two stages?

[Luis H]

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

Well, I guess I am not sure about the Snark and some of the other Nemrod designations.

Here is the Snark III Silver that I was thinking of.
Snark III Silver

Sorry, I could not find larger pictures.

This regulator was always advertised as having three stages.

Here are some specs:


Hersteller / Manufacturer: Nemrod
Name: Snark III Silver
gebaut / built: unknown
max. Luftlieferleistung / max.air delivery: > 400 l /min.
Stages: 2 (3)

Stage 1: Upstream
Balanced?: no
Type: membrangesteuert / Diaphragm activated
Mitteldruck / IP: 7,5 bar
HP-Port: no (early), 1 (newer)
Stage 2: Upstream
LP-Port: 1 (later)
Gehäuse/Housing Messing verchromt
Membrane Ø / Diaphragm Ø: 11,5 cm
max Druck / Pressure: 200 bar
Anschluss/Fitting: DIN / INT
Luftauslass/ Air outtake: Runddichtung Gummi / Mushroom rubber
Mundstück/Mouthpiece: Einwegeventil Gummi / non-return rubber
Special notice: The engraved model had no HP-Port, the later ones had - the LP-Port was added on the last regs (optional to the older ones) Hose length 550 mm, weight 2044 gr.

 

[pescador775]

Taylor, you might wish to read some of the other posts before jumping in.

Thalassamania, the Snark III was indeed a dual hose, two stage regulator manufactured by NEMROD, SPAIN. The body and hoses were extremely rugged. Invented in 1946 and using a primitive design, the regulator was, nevertheless, very reliable. Unique among two stage regs, it employed compound levers and a strong venturi jet to blast by the rather small non-return valves and create easy inhalation. Dive shops were still selling new Snark III regs as late as 1976. Later models of this reg included a high pressure port for installation of an SPG.

 

[scubafanatic]

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.

....that would be pretty neat, eagerly awaiting 'the three stages', definitely MOE for your money!

 

[captain]

The Nemrod Snark III was in use by the US Navy into the 1990's for preparing SEAL's for rebreather training. With production and support of the Snark III coming to an end in the early 90's the Navy comissioned U S Diver or AquaLung, what ever they were call at the time, to developed a two hose regulator to replace the Nemrod Snark III. The result was the two hose Mentor which was produced in limited quanties for the Navy and was never available on the civillian market.
Aqua Lung may have been more sucessful at reintroducing the two hose regulator by making the Mentor available on the civillian market rather than the cobbeled together Mistral that was the worst of both single and double hose regulators.

 

[kouhoutek]

Wow!

I had no idea my post would generate this much interest.

Thanks for all the answers, especially the insights into the earlier days of scuba.

From the responses I read, it seems that safety and reliability are pretty much a wash between two. The real driving factor is the engineering. It is just easier to design a good performing demand valve from 150 psi than from 3000, and this outweighs the simplicity of a one stage design.

 

[Nemrod]

What year was that comet and when is it expected back? I don't recall.

N