Scubapro Regs... What's the difference? Which one to get?

[halocline]

Well, that about says it, doesn't it...another extremely informative post by DA Aquamaster. I'm still not exactly sure of the advantages of a balanced 2nd stage; if the 1st stage is providing a stable IP (balanced first stage) doesn't an unbalanced 2nd stage provide the same breathing response throughout the dive? I can sort of understand the advantages of having the higher flow rate 2nd stage, if your 1st stage is capable of delivering high flow.

I guess I would add that if you're both novice divers, I'd save your money and get the MK2 R190. That's what I bought after reeling for awhile in the array of choices out there. The bottom line is that you'll probably be very hard pressed to tell the difference in the environment you'll be diving in between it and a high performance reg; you can be confident that it will not scew up on you, ever, (only a few moving parts in the 1st stage) and you can put money into more diving. Maybe after a few years' experience you'll want a specialized reg for specialized situations.

 

[divematt]

Thanks DA Aquamaster, that was an awesome explanation. I guess we're now leaning towards the G250 with the MK25 or the MK16. Heck, I have an old G250 now and figure it's time to replace it. What about that 400 you were talking about? Do they still make it? Is it worth trying to find one of those older ones that I saw you talking about somewhere here. You said that they were better years ago than they are now due to some part that was brass then and now is plastic? If not, we'll just keep it simple and go with what I spoke of above.

Thanks again,
Matt

 

[Deep Sea Alan]

To "Da Aqua Master"
Great Post!

Alan

 

[FireM]

I have Mk18 S600/R290 and I think it's exelent reg. Dive in all conditions (worm, cold, icy). My maximum depth with this reg was 50m (164 ft)..

 

[DA Aquamaster]

I'm still not exactly sure of the advantages of a balanced 2nd stage; if the 1st stage is providing a stable IP (balanced first stage) doesn't an unbalanced 2nd stage provide the same breathing response throughout the dive?

Yes. And in fact with proper adjustment, the R190 and R390 can perform really well. SP specs detune them a bit more than they need to be which is unfortunate.

The advantages of balancing the second stage are that it can use a lighter spring to hold the seat against the orifice as in a balanced second stage only a portion of the force comes from the spring, the rest comes form the air in the balance chamber on the other side of the poppet.

This has two potential advantages. The first is that the lighter spring will not be as likely to engrave the seat in the second stage as soon. The second is that since the size of the orifice. In an unbalanced seocnd stage, a larger orifice would mean astronger spring would be needed as all of the downstream force acting on the seat has to be countered with spring pressure. This in turn would require a longer lever and a larger diaphragm to keep the inhalation effort low. Consequently the practical limit in terms of orifice size is fairly small.

With a balanced second stage, the diameter of the balance chamber side of the poppet can be increased in the same proportion as the size of the orifice. So a larger orifice can be used in a balanced second stage as the extra force to offset the downstream force on the seat can be provided by the balanced poppet using a small and light spring so a longer lever or larger diaphragm is not required.

On the other hand, a conventional unbalanced downstream second stage like the R190 or R390 is very simple and easy to service. And if you do end up with a second stage seat that has an excessive seating groove causing a slight freeflow, you can screw the demand valve body out of the case to expose the demand valve stem and then just flip the soft seat. Not SP approved of course, and you still have to know how to re-adjust the orifice, but it is still an effective way to save your dive trip if the need arises.

SP used to offer unbalanced Adjustable second stages and they did provide a lower cost option for obtaining an adjustable second stage without ponying up the bucks for a balanced second stage. The cool part was that if you wanted to later, you could upgrade them to Balanced Adjustable second stages.

 

[DA Aquamaster]

Thanks DA Aquamaster, that was an awesome explanation. I guess we're now leaning towards the G250 with the MK25 or the MK16. Heck, I have an old G250 now and figure it's time to replace it. What about that 400 you were talking about? Do they still make it? Is it worth trying to find one of those older ones that I saw you talking about somewhere here. You said that they were better years ago than they are now due to some part that was brass then and now is plastic? If not, we'll just keep it simple and go with what I spoke of above.

SP discountined the D400 at the end of the 2003 season which is too bad as it was, in my opinion, one of the best second stages they ever made. But opinions varied widely and a lot depended on whether the tech who worked on them knew what they were
doing. They were different to work on and many techs did not like them and could not really make them perform to their potential. The move to plastic orifices in about 1996 did not help tthe situation either as they were harder to fine tune than the earlier D350's and D400's with the one piece brass orifice and aspirator body.

From a tech perspective I can understand why SP went with the X650 and a linear poppet assebly similar to the G250 and S600. But unfortunately they missed the mark with the exhasut valve design and case geometry.

If you can find a tech who likes the D400, they it is worth finding one as the tech will no doubt be able to make them perform. If the tech hates, the D400 it's because he does not fully understand them and it's a good indicator that he probably can't make them perform well.

 

[Kamala]

Wow! That's a lot of information to chew on. DA Aqua, thanks for the total breakdown! Anyone know off hand how cold it gets deep in Puget Sound (past 60 feet, up to 100) or same depth off of Vancouver Island?

 

[Hoosier]

Da Aquamaster.

I am so impressed at your post again. Without permision, I save your post in my knowledge folder. Thank you.

BTW, I have One quick question:

So, do you think SP MK16/G250 is the better choice for the cold water environment than Poseidon, Atomic B1, Apek 200X, or AL Legend Supreme?

 

[BigBoB]

I have had my mk25/s600 down as far as 315 feet....no problems yet. I love the combo best I have ever owned.

 

[DA Aquamaster]

So, do you think SP MK16/G250 is the better choice for the cold water environment than Poseidon, Atomic B1, Apek 200X, or AL Legend Supreme?

I think all of them would serve you well in cold water. Poseidon's are different and are an acquired taste. I have never really liked the way they breathe, but it's a highly subjective thing. They are pretty cool from an engineering standpoint.

I like the Atomic B1 as it is a very good performing balanced piston design (with much in common with SP designs). It uses the tried and true freeze protection method of filling the ambient chamber and keeping the lubricant contained with a rubber boot. This is the same (non-Scubapro approved) approach that I use on my personal Mk 20's. The TIS/AF kit just is not 100% reliable on the Mk 20 and Mk 25 while a filled ambient chamber and SPEC boot is, as long as you keep the chamber filled periodically.

I have also been impressed with quality and performance of the Aqualung Ledgends I have worked on. Very nice reg.

I have only seen the Apex 200X but it's quality appears equally high.