Downstream vs. Upstream Regulator Design

[CharlieDontDive]

Are there any downstream 2nd stages on the market? If so, what's the advantage?

 

[Ayisha]

Most regs are downstream, which means that the seating mechanism sits downstream of the orifice. If the reg fails, it will fail open, causing it to freeflow.

If upstream regs fail, the seat would be pushed closed against the orifice, so it fails closed. As in, no gas.

There's a reason almost all regs currently manufactured have downstream second stages. We should all have learned to deal with a freeflow in o/w. So the advantage is that if the downstream reg fails, it fails open and still gives you air - it still supports life.

 

[Eric Sedletzky]

The only advantage to an upstream second stage that I can imagine is that in the event of a second stage failure it fails shut and you don’t lose a bunch of critically needed gas. Other than that I think they seem creepy.

 

[happy-diver]

Yeah you're right Eric, creepy

 

[rsingler]

If there was perhaps some confusion about upstream versus downstream, there are two excellent upstream regulators currently being sold : the Poseidon Jetstream and the Hollis 500se.
The manufacturers largely pooh-pooh the fail closed argument, and the robust Jetstream has been tested by the U.S. Navy to over 600 feet. It is approved in the EU for a similar depth, which speaks to its quality.
The Hollis has an even better servo design, in that the servo valve is a downstream valve which will not fail closed even if the main valve is an upstream valve. I dived the 500se in the Cayman Islands last year and absolutely loved it. Unfortunately, support for these Hollis products is dwindling rapidly after the sale of the company to Huish.
The breathing characteristics of these two regulators is different, in that you don't "sip" from the valve. It opens briskly and gives a significant amount of air, especially at depth. That is one reason it is favored by some groups for technical diving. But consequently, the way it delivers air yields two camps: fanboys and haters. But it's not "better or worse". It's "different".

 

[Eric Sedletzky]

If there was perhaps some confusion about upstream versus downstream, there are two excellent upstream regulators currently being sold : the Poseidon Jetstream and the Hollis 500se.
The manufacturers largely pooh-pooh the fail closed argument, and the robust Jetstream has been tested by the U.S. Navy to over 600 feet. It is approved in the EU for a similar depth, which speaks to its quality.
The Hollis has an even better servo design, in that the servo valve is a downstream valve which will not fail closed even if the main valve is an upstream valve. I dived the 500se in the Cayman Islands last year and absolutely loved it. Unfortunately, support for these Hollis products is dwindling rapidly after the sale of the company to Huish.
The breathing characteristics of these two regulators is different, in that you don't "sip" from the valve. It opens briskly and gives a significant amount of air, especially at depth. That is one reason it is favored by some groups for technical diving. But consequently, the way it delivers air yields two camps: fanboys and haters. But it's not "better or worse". It's "different".

I think @tbone1004 mentioned he has a dive buddy that said something to the effect of he would “rather drown” than have to breath off one of those servo type regs. In tbone’s case I think he’s talking about Poseidon’s.

 

[rsingler]

Ah, haters!

 

[happy-diver]

Yeah like these ones too been sitting around just plugged them in

You take a breath then pause your lungs have collapsed waiting waiting then the Poseidon reg activates
slams air down into your lungs like something pneumatic pause waiting waiting and then you start again.

Ha perhaps up around the Baltic States in freezing conditions they behave differently or for the Services

 

[Bob DBF]

The upstream seconds are usually used with an over pressure relief, in case the first fails with a high IP. In the case of the old Poseidon Cyklon I picked up, it had a downstream second, a 109 as the alternate. I heard Posiedon's don't play well with others, however it seems to have made friends with the 109.

I am not a hater, but my loyalty is to Sherwood.


Bob

 

[rsingler]

Yeah like these ones too been sitting around just plugged them in...
You take a breath then pause your lungs have collapsed waiting waiting then the Poseidon reg activates
slams air down into your lungs like something pneumatic

Sigh. Where have I heard that before? Some "diver" takes his gear out of a closet where it's been sitting (a discontinued model, no less), tries it out for the first time in years, and then complains that it breathes like a pig. Yeah...must be the regulator.