Scubapro S600 WOB exhale effort

[davehicks]

Most of the time I dive on a closed-circuit rebreather, both at home and one trips. Occasionally I make a trip to a destination that does not have easy access to CCR supplies and dive open circuit. Due to the pandemic, it's been a while since I dove OC on a trip in February 2020 to Galapagos. I have a trip coming up next month to Fiji and plan to bring my OC gear.

I decided to put together two sets of OC regs for our trip. Given the time since my last OC trip all my regulators have been mixed, swapped, stirred, and shaken up all over the place. I decided to put together two sets with Mk25 1st stages and an S600 primary. Secondaries were an odd Atomic Z2 and Apex TX50. I also have a pair of G250v 2nd's that I've been using for bailout bottles with the CCR's.

I started out putting together the Mk25 rigs and getting the S600's tuned and balanced. No problems there. I did a little tear down and cleaning but no parts swaps as they had not been used much since their last service a couple years ago. While testing both of the S600's I was surprised to find that the Exhalation Effort was quite hard. The inhalation effort was fine after the tune up but the exhalation on both of the S600 felt a little like blowing up a balloon. I would expect it to be effortless, but it feels like more work than expected.

I tried the other 2nd's on hand (Atomic Z2, G250v, Apex) and they all breathed much better than the S600's. Exhale is far better on all of them. The G250v has a much better work of breathing on both inhale and exhale. So much better that I have ditched the S600's and will bring the G250v regs as our primaries.

This was all evaluated out of the water. I will try them in the pool today to do one more comparison between the S600 and G250v.

What do I do with these S600's? I know how to tune up a regulator for easier breathing, but what if it has a rough exhale? Is this just a result of the body design? Is the exhale mushroom valve old and stiff? Has anyone else experienced this issue and come up with a solution?

 

[Nemrod]

Look inside the exhaust tee and see if that, for lack of a better term, divider, is touching the valve.

You could need new valves but they last an awful long time. I imagine what you notice will go away in the water.

The 250Vs on the Mark 25 are your better choice IMO. And the S600 set for back up. My very limited pool (22 feet deep!) experience with a CCR is that they breath like a DH regulator or like a snorkel, slightly hard inhale and very easy exhale. Single hose regs are easy inhale and slightly harder exhale due to the exhaust valve being below the mouthpiece (dependent upon swimming position). Maybe you just need to re-acclimate .

James

 

[Geo7]

Ok, here is some speculation: I assume we are talking about the elastic tension of the mushroom valves that is a function of their shape, since the opening cutouts are similar (except Atomic with their sophisticated oval geometry), and the regs are clean and the valve does not stick to the case.

I remember @rsingler D420 videos on youube where he showed that Scubapro uses the tension of the mushroom valve to help seal the second stage against the internal reg pressure exerted by the "case geometry fault". In other words, when you look down, a reg set at 1.2" cracking effort tends to bubble. But not if the mushrom valve has some elastic tension sealing it against the case.

If I understood Rob correctly, Scubapro might be tuning the whole system so that while looking down or almost straight down, the reg can be set at 1.2" (mine are even lower) and be bascially effortless in inhalation? Exhalation also changes based on position in the water.

So my question is whether it is possible that the apparent high exhalation resistance you observed on land is purposefully designed for the most common diving position?

 

[davehicks]

It a good theory. I tried the regs in the pool and the effort of exhaling the S600 was not quite as noticeable. However the G250v was better on inhale and exhale by a good measure.

I decided to rotate my G250v regs to tropical open circuit roles and put the S600s on my CCR bailouts.

 

[Geo7]

Yeah, the G250 / G250V is the gold standard. I do like the small size of the S600 as a backup / octo / stage / bailout reg though...

 

[Nemrod]

Somewhat incredible but then again perhaps not that after 42 years the Scubapro G250 remains at the top of the heap and is still in production from Halcyon as the Halo and under the Scubapro brand masquerading as the G260 which is a G250 fancied up.

James

 

[Geo7]

While I like my S620ti, the smoothest breathing reg I ever had was a G250 Graphite where all the parts magically matched.

Following Rob's latest Regulator Geek discussion, I wonder if Scubapro now tries to offer a more balanced experience and focus their efforts on a very well behaved venturi effect through the flow rate range. I might be in a minority, but personally I always liked aggressive venturi. After all, the VIVA vane is right there to adjust as desired!

Halcyon was smart aquiring the G250V rights. Also the G260 seems great, though I have not used it. But I suspect that both have a slightly reduced venturi effect compared to the original.

 

[Nemrod]

The G260 seems on par with the G250. I have only three dives on my G260 set because I used my Number 1 G250 set for most of my dives in my month long SoFla sojourn. The G260 as they came were a little stiff so when I got home I took them down and adjusted per the manual and my usual practice. I have not had them back in the water yet, will in about 10 days, but it seems about like my best G250 set. The micro-adjust is a nice feature I guess but I could live without it but I did use it to drop spring tension while maintaining lever height. Out of the box both were around 1.4 on my Magnehelic and now I am at about -1.1 with the adjustment knob in 1/2 turn. Turned fully out I have them set to just barely dribble and it is just instant air adjusted so.

Along Conch Wall a couple of weeks ago:



James

 

[grantctobin]

I decided to rotate my G250v regs to tropical open circuit roles and put the S600s on my CCR bailouts.

Great, let’s put the regs that you think are less appropriate or can’t tune to your liking on the bottles you unequivocally need to function when the turds hit the fan…

 

[Geo7]

I'd argue they are all stellar, but some just feel nicer?