Anyone familiar with PST- Scubapro lp40's/2015 psi's?

[Ghetto Diver]

Got them back and have a couple of dives on them.
They are near neutral at 300. I zip tied 3lbs to the pack then 2 pounds on next dive (no wetsuit used) with good results.
They are fun to dive..and have quickly become my favourite rig for shore diving. Pack positions the DH can just right.
It was quite liberating to dive with no add ons: bc, spg.
I understand why there is no reserve on the manifold now...the Healthways has a restrictor in reg that makes breathing a bit stiff at 300 psi approx.
I inverted the yoke and had to drop the SS bands to fit the HW as it collided the backpack.

13cf for scale

 

[simonbeans]

By the time that backpack was marketed, double hose regs were out of fashion. The earlier health ways plate style was designed more for DH regs. Or a simple harness. Yours was more for those silly single hose regs.

 

[Bob DBF]

I understand why there is no reserve on the manifold now...the Healthways has a restrictor in reg that makes breathing a bit stiff at 300 psi approx.

The reg is most likely unbalanced and that makes the breathing a bit stiff at low pressure. K-valves were used before, during, and after j-valves were prevalent. It depended if you you wanted to spring the extra money for a j-valve when they were available.


Bob

 

[Luis H]

The reg is most likely unbalanced and that makes the breathing a bit stiff at low pressure.

Bob

That is an upstream single stage regulator. That type of design actually gets easier to breath as the tank pressure goes down. If it is getting harder to breath at low tank pressure, it is because it has a restriction orifice in its intake.


In the case of two stage regulators, the typical vintage unbalanced diaphragm first stage (used in all US made DH regulators) will get easier to breath as the tank pressure goes down (if it has a down stream second stage, like an Aqua Master). The IP from the unbalanced diaphragm first stage goes up as the tank pressure goes down.

The two exceptions that I can think of are some of the Sportways and the Nemrod Snark III. They both have unbalanced diaphragm first stages and the IP will go up, with decreasing tank pressure, but they also have upstream second stages.

 

[Bob DBF]

I started on the Snark III, figured others were similar. Back to the books!


Bob

 

[John C. Ratliff]

This post was messed up, so I tried to fix it and couldn't. It should be deleted.

SeaRat

 

[John C. Ratliff]

That is an upstream single stage regulator. That type of design actually gets easier to breath as the tank pressure goes down. If it is getting harder to breath at low tank pressure, it is because it has a restriction orifice in its intake.


In the case of two stage regulators, the typical vintage unbalanced diaphragm first stage (used in all US made DH regulators) will get easier to breath as the tank pressure goes down (if it has a down stream second stage, like an Aqua Master). The IP from the unbalanced diaphragm first stage goes up as the tank pressure goes down.

The two exceptions that I can think of are some of the Sportways and the Nemrod Snark III. They both have unbalanced diaphragm first stages and the IP will go up, with decreasing tank pressure, but they also have upstream second stages.

Luis,

You are correct about the single stage Healthways double hose regulators. They will get easier to breathe at low tank pressures.

Concerning the Sportsways and Nemrod Snark III, yes, both are diaphragm first stages. For the Sportsways, their first was called a Dual Air, and it had a tilt valve second stage. It would breathe slightly harder with the unbalanced diaphragm first stage, where the interstage pressure went up. Later models were the Hydro-Twin and Hydro-Twin II. The former was again an unbalanced first stage, with the regulator breathing slightly easier at low tank pressure. But the Hydro-Twin II had a balanced first stage, so the interstage pressure doesn't change, and it is unaffected by interstage pressure changes.

The Nemrod Snark III is a different "cat," so to speak. It features an unbalanced first stage, with an upstream second stage like is on the USD Mistral's single stage. It has a "third stage," which is actually an overpressure relief valve. It is supposed to get a bit harder to breathe at low tank pressures due to higher interstage presure, but that is largely overcome by the extreme leverage of the duel lever system, so it really is not felt. I have a modification which channels the air off the diaphragm and down the intake hose, which improves the venturi of the Snark III. Also, there is now out of Turkey a new first stage, with LP and HP ports and a balanced first stage to modify the Snark III into a completely new regulator.

SeaRat

 

[Ghetto Diver]

SeaRat...I had a Snark III and did the modification you did [after I found your original post with some digging after I bought it]. It helped. I wound up selling it for a decent profit..AFAIK, the guy is still using it with the add-on.