1st Stage-Sidewinder

[tbone1004]

Machined brass.

never seen those, can you post some pix?

[FW]

never seen those, can you post some pix?

Machined from a brass rod. I use silicon sealer to keep the threads from leaking. I have a couple spares, if anyone needs one.

[PeterVICEG]

I am not sure that is a good 1st stage for a SideWinder. The SideWinder is supposed to have an O2 reg with the diaphragm blocked. They come with a 1st stage with a cap over the diaphragm, so it will be constant mass flow, instead of constant IP.

Jason is using it with a needle valve.

[rddvet]

What makes Poseidon regs so amazing they're worth all of those headaches.

[oya]

What makes Poseidon regs so amazing they're worth all of those headaches.

Nothing.

I own something in the range of 30 Poseidons. Love em. And use them for nearly everything.

If I needed a fixed IP I?d get something else. Like a sane person.

[FW]

Nothing.

I own something in the range of 30 Poseidons. Love em. And use them for nearly everything.

If I needed a fixed IP I?d get something else. Like a sane person.

Best answer yet

I bought the first stage recommended by KISS. From the KISS website "1 oxygen first stage with Delrin plug & OPV installed." Note the "plug" part.

[DA Aquamaster]

As I recall KISS recommends an Apeks DS4 oxygen first stage and includes a disc that replaces the hydrostatic pressure transmitter to convert it to a non depth compensated first stage. That's the quickest, easiest and most idiot proof way to go.

The flow rate through the orifice is then adjusted by adjusting the intermediate pressure of the first stage.

In this application you should be using a balanced first stage - or at least something close to it.

I used Scubapro Mk 17s on our Sidekicks mostly because I had a couple sitting around and partly because they were pretty easy to modify. I fabricated a disc from stainless steel sheet and then brazed the disc to inside of the brass retainer for the external diaphragm that seals the ambient chamber.

In the finished piece, the external diaphragm still provides the seal, the stainless less steel disc and retainer just prevent any pressure transfer. The two washers sit between the pressure transmitter and the main spring adjustment screw. They lift the transmitter off the internal diaphragm spring pad and prevent any pressure transfer, land et the transmitter support the external diaphragm, so that even if the stainless steel disc failed, it will still be a constant IP first stage. To get depth compensation both the stainless steel disc and the external diaphragm have to fail so it's a redundant design.

----

The Scubapro Mk 17 is not however perfectly balanced. For example, if the IP is set at 135 psi at a supply pressure of 3000 psi, at 500 psi the IP will be about 145 psi.

As a result of the less than perfect balancing, the first stage slowly starts feeding a bit more O2 as the tank pressure gets lower. In practice, I start at 3000 psi and end most dives with around 1200-1500 psi left. However I also set the IP to provide optimum flow at around 2000 psi, so the shift is only a couple psi each side of that optimum flow rate.

Worst case on a swimming dive, I might need to tap the manual add every 15 minutes rather than every 20 early in the dive, but that's the only downside. If I am doing a really long dive, then it's also a dive where the bottom 1000 psi or so of the O2 tank is spent on deco. Since I'm not swimming I already have excess flow and at 20' I can just close the inline shut off.

[FW]

As I recall KISS recommends an Apeks DS4 oxygen first stage and includes a disc that replaces the hydrostatic pressure transmitter to convert it to a non depth compensated first stage...

Mine has a standard Chinese 1st stage, with a disc blocking the diaphragm. Pretty much the same as HOG, DeepSix, etc.

[rchrds]

Yep, I'm not particularly a fan of the integrated valve/first stage. The one I was using had a fill adapter with an internal check valve (they all do) which made it nearly impossible to fill safely with a booster. It would fill no issues up to my supply gas, but then as the booster took over, you had to boost to 3800 to overcome the check valve and end up with 3000. Not too safe in my book. I suspect other check valve assemblies are similar.

As Peter has said, I no longer use the simple orifice. I use a needle valve, so the non-compensated first stage isn't an issue. Frankly, it wasn't much of an issue with the orifice down to 300, but YMMV. Go with what you were trained until you know otherwise. Highly recommend the needle valve- Mike has a new one with a clicking knob so you can count the number of clicks, or if you don't mind fiddling for the first 15 minutes-1/2 hour the swagelog style needle valves are just fine. I like the look of the new locally produced one linked on the first page.

[rchrds]

As a result of the less than perfect balancing, the first stage slowly starts feeding a bit more O2 as the tank pressure gets lower. In practice, I start at 3000 psi and end most dives with around 1200-1500 psi left. However I also set the IP to provide optimum flow at around 2000 psi, so the shift is only a couple psi each side of that optimum flow rate.

Worst case on a swimming dive, I might need to tap the manual add every 15 minutes rather than every 20 early in the dive, but that's the only downside. If I am doing a really long dive, then it's also a dive where the bottom 1000 psi or so of the O2 tank is spent on deco. Since I'm not swimming I already have excess flow and at 20' I can just close the inline shut off.

Or go to a needle valve. Adjust as your workload varies (swimming/scootering/deco).