What are 1st and 2nd stage pressure drops?

What psi's do the 1st and 2nd stage regs drop tank pressure to?

Is it a industry standard that all 1st and 2nd's drop to the same psi's?

First stage drops the pressure from tank pressure to intermediate pressure, which is usually in the 130 to 140 psi above ambient range. But it is not standard -- I believe, for example, that Poseidon regs use a slightly higher IP. The second stage drops the pressure from the IP to ambient, and that's standard

Common IP, (Intermediate or Interstage Pressure) for first stages is 125-145psi. Unbalanced piston firsts will often drop 20 or so psi over a tank, so if you set the IP at 145 at 3000psi supply pressure, when you are at 500psi supply pressure, your IP is 120-125. This is noticed by the reg breathing "stiffer" or harder as the tank pressure goes down. Not as noticable with an "air balanced" second stage, but they are not perfectly balanced, so it is slightly noticable.

Unbalanced diaphragms, on the other hand, have the IP creep upward with the loss of tank pressure. This is due to the different design of the regs. (Upstream/downstream.)

Balanced designs, whether piston or diaphragm, claim to maintain a steady IP over the entire tank-pressure range. Some are better than others, and a creep of say 5 or 6 psi is within tolerance for some "balanced" first stages. Well designed first stages will have zero creep or near zero. This will make tuning the second stage easy and can make a cheaper or "budget" second stage perform better since it can be tuned higher with more predictability, since the IP isn't swinging as much.

Also, usually, the higher the IP, typically, the higher the flow and "performance" of the second stage. Higher IPs "breathe" easier.

Regarding Poseidon IP: Only one model, the Cyklon, uses a high IP. The balanced Cyklon first-stage IP is 174psi v. the typical 125-145 of most regs. The newer Poseidon Jetstreams and XStreams all run a 123psi (8.5bar) IP. Older unbalanced Cyklons (Cyklon 300) were set at 181psi. Also, the Cyklon IP is set at a tank supply pressure of 300psi, since it was an unbalanced diaphragm, and went higher as tank supply went down, (at 3000psi, mine would be at 155-160psi). This meant that the reg breathed better the lower the tank pressure went, (being an unbalanced second stage). The new balanced Cyklon first stage is also set at 300psi.

The reason for this was that the Cyklon was developed in 1958, when really the only breathing gas used was air. (Military and commercial experiments/work with Nitrox, Hydrox and Heliox don't count). Since the increase of density means the breathing gas "thickens" with depth, (and air gets thick compared to helium mixes), the high IP and large hose orifices allowed the Cyklons to deliver enough gas to the diver that he didn't "over-breathe" his reg, which could happen on some older designs. It's a big reason why the Cyklons still have a reputation for being great breathers, great "tech diving regs", "they breathe better the deeper you go", etc. And they are still in production with only evolutionary changes. Testament to the original design.

But TANSTAAFL, right? The counter-points are that the high IP precludes the use of conventional octos on Cyklon rigs, (high IP would cause the octo to freeflow, and if de-tuned to "normal IP range", the Cyklon to breathe like crap), good techs are hard to find, parts CAN be expensive, (but not necessarily so), the higher IP wears internal parts of the reg faster, Poseidons use proprietary hoses, so you're stuck buying their hoses, or using adapters, which I don't like, etc.

Think that about covers most of that. I'm sure other reg-heads will be along shortly to fill in any gaps I missed, or correct things I crossed up.

50Fathom, thank you! I learned something. I only vaguely remembered that there were Poseidon regs with higher IPs, but I had no idea why.

TSandM:

50Fathom, thank you! I learned something. I only vaguely remembered that there were Poseidon regs with higher IPs, but I had no idea why.

Click to expand...

No worries! Glad I could help out.

I like Poseidons, even though I'm selling mine off for philosophy-compliant regs, and I just wanted to dig into the whole "Poseidons run a high IP" thing, since it causes so much confusion among a lot of people. It's only one model. The others are "normal" IPs. But for some reason people hear "Poseidons run a high IP" and they assume they all do it and that it's some kind of negative thing. It's not really a positive or a negative, it just is what it is.

Glad I could be of service!

Doesn't it mean, though, that the Cyklon first stages aren't compatible with the run-of-the-mill second stage? Which would be a big reason why DIR wouldn't like them . . .

The first stages are fine, since they are diaphragms and the IP is adjustable with a hex wrench. You can set it from ambient all the way to 300+. It depends on how you adjust the spring cover, like all diaphragms.

The ports are standard 3/8" LP and 7/16" HP as well. I recall reading on the old tech-diver lists that George used Poseidon first stages with ScubaPro seconds. Poseidon first stages have been used and accepted by the WKPP (at least 15-20 years ago), the big issue with Poseidon is the second stages. The Cyklon uses a proprietary connection on the second-stage, (slightly larger internal diameter than your "typical" second stage hose, and the threads are metric), along with the second-stage requiring a high IP since it's unbalanced.

The newer Jetstreams and XStreams run an acceptable IP, but they are upstream second-stages, (servo-assisted tilt-valves), and use proprietary hoses with OPVs built into the hose in case of a HP seat failure, so the hose doesn't explode or the reg doesn't fail closed. They're incompatible with other regs and the OPV is an additional failure point. The seven-foot hoses also cost between $75-125. Each. Even the short hoses are $40-50 and the shortest they come is 70cm lengths, (28"), which means the backup is an "elephant-ear" way out on your shoulder.

A Cyklon was my first reg ever and I do love it. I later got XStreams for doubles and singles, along with a deco reg. I LOVE the performance, and they deliver an insane volume of gas, being certified in Europe down to 200 meters, the only reg to be so.

On the other hand, they don't pass muster for DIR, and I now work in a Scubapro shop that allows obscene staff discounts, plus I got certified as a Scubapro tech, so now I have access to cheap regs, parts kits and I can work on them myself. Win-win.

Why pay retail for regs, and have them sent off for someone else to work on them since I can't get parts, when I have the above? It makes financial sense at least. I think Scuabpro makes good regs, but I'm not an insane fanboy.

I love to dive and explore the underwater world. To me the gear is a means to an end. It's what allows me to get down there. So many people, (myself included at times), get hung up on brands and names and will argue until the cows come home about "the best", but it doesn't matter. It's gear, it gets me in the water. I want what is the best, most available, highest-performing that I can get reasonably. Right now, circumstances are making me a "Scubapro Man", but later, who knows?

To me, gear is tools, and I'm reminded of a bit from the intro to Cousteau's last book, The Human, the Orchid, and The Octopus, by his collaborator Susan Schiefelbein, "Invention is nothing more than the tool of the explorer. If you need something, you make it. The tools are there to serve a purpose and have little inherent value. When equipment was no longer needed for the current mission, it was discarded or or used to foster support for the next big thing."

That's one thing I like about DIR/GUE. They don't tell you a brand to buy, (though this is apparently not understood by some people), but certain criteria that your gear must meet. As long as it meets the specific criteria, you're GTG.

Thanks 50Fathom, I learned something as well even if I will likely never own a Cyklon....