Hi Kupu
Congrats for your GDS Pioneer reg.
First thanks a lot!
Mentioning the GDS Pioneer you reminded me that years ago I bought a 2nd like that for very little money in the bay, but didn’t recognize it as a Scuba 2nd and forgot about it.
Yesterday I looked for it and really I found it in my workshop ( so I didn’t leave it in my workshop in the Carribbean).
It’s in fact a GDS Pioneer 2nd, just missing the exhaust tee.
So I dismantled it, cleaned it and put it back together. When I tested it I realized that it has a crack in the body at the hose connector, so I will first have to see how I can seal the crack before really testing it.
But anyway I guess I can guide you through the procedure and explain you how it works.
You explained correct that the Pioneer 2nd is an upstream model, at least the small pilot (servo) valve.
The main valve opens with the incoming air flow, so should be considered as a downstream valve.
The main valve orifice is the hole in the center of the 2nd stage body, so the air, coming from the side, has to flow first 90 degrees towards the orifice and then back 180 degrees to the mouth piece
The tiny pilot valve spring just keeps the pilot valve in position, of course it cannot close the main valve against whatever IP. The LP seat sits loose in its fitting, so when the IP hits the seat, the valve first is open.
What you probably overlooked (in my Pioneer it is very easy to see, in contrast to my Spinnaker, where I could not recognize it even when I thought it must be there), is the tiny hole in the LP seat which let the air from the 1st enter the space behind the seat, putting pressure on the upstream pilot valve and then on the LP seat, which is pushed back towards the orifice and closes it ( this is why first you have always a short free flow before the main valve is closed).
When you are inhaling, the lever of the pilot valve will open and release some air into the space under the diaphragm, producing a vacuum in the space below the pilot valve. The LP seat follows the lower pressure and opens the main valve until the inhaling process is finished. Then the cycle starts again.
That’s how I understand it from what I see. Basically it is quite similar to the Poseidon Jetstream and Tekna 2100 2nds.
When I dismantled yesterday the pilot valve of the Pioneer, I found a lot of rust on the metal lever ( unfortunately I didn’t make photos of that), no way it could seal. I put it in the Ultrasound and the I removed the rust as good as could with a Dremel, but I think I had some material loss on it. Anyway after the procedure it sealed again.
Also I realized that the tiny hole in the LP seat was clogged, I couldn’t get air through with the air gun.
So I used a fine needle to remove the obstruction.
I had been pretty lucky that the Spinnaker I purchased, obviously had never been used, so everything is working flawlessly after I had put it together again (CE 0,8inch/h2o at static IP, 1,1inch/h2o at 12,5 SCFM flow, without venturi assist!)).
I used the 4bar IP to which the Spinnaker 1st was adjusted and Angelo was mentioning in another thread.
For basic testing of the Pioneer I used Conshelf 1st, but with 4bars IP the Pioneer 2nd kept on free flowing. When I increased to a bit more than 6bars (95psi) the valve closed, so I guess the Pioneer 2nd needs a higher IP than the Spinnaker, maybe somebody around knows…….
For me the Pioneer and Spinnaker 2nds are a pretty unique design, when rinsed well then two almost maintenance free 2nds. I don’t think that you need a new LP seat, in contrast to downstream 2nds the Pioneer 2nd main valve is open when not under pressure, so probably it will not be grooved very deep.
So good luck with your baby, I would love to get a Pioneer 1st in my hands ( maybe one day)!
