decisions with SP reg pls

[batman diver]

batman, just to throw 1.5psi into the ring here... when I was working in a place where my 'other' brand regs were not supported, I wound up stealing a mk2+ out of the rental fleet, throwing a service kit at it, and hooking up my balanced 'other' second stage. Save a slight hesitation (may or may not have been real or imagined, just my experience) the top of the line second stage ironed out most of any deficit that might have been attributable to the 'lesser' capabilities of that Mk2. That being said, they are stupidly easy to work on, and even in a daily use rental environment, the -2 will often take 2 years before misbehaving and thus asking for a service.

I would not hesitate to shave a few bucks if budget was tight. The reg is bulletproof; there is a reason they are such common rental regs.

The LDS says can't buy 2nd and reg seporate , and now they told me also that the g250v won't work with the mk2+ summit about it not supplying enough air ... Is this true

 

[Zung]

This is true... BS.
According to SP's official manual, the MK2+ has a flow rate of 92 CFM and the G250V's is 57 CFM.

Don't let them scare you away with their techno-babble. The combination is unusual perhaps, not profitable for them for sure.

That being said, it's also true that the usual practice is to sell a higher end 1st stage than the 2nd, because a balanced 1st is better equiped to deliver a constant intermediate pressure (IP) than a balanced 2nd to cope with a declining IP from a non-balanced 1st. In other words, balanced 1st + unbalanced 2nd is potentially better than the otherway around, which is your proposed configuration.

 

[batman diver]

I see , I thought so , were did u find those flow rate things , would be very interesting to look at , I think I'm gonna try a different dive shop maybe, see what they can say , really want that g250v now , it also looks so awesome

 

[Zung]

Here.
Also search this board for SP, flow rate, and everything by DA Aquamaster: THE Mister Encyclopedia.

 

[herman]

The LDS says can't buy 2nd and reg separate, and now they told me also that the g250v won't work with the mk2+ summit about it not supplying enough air ... Is this true

Find a new shop, you have just been fed a large load of BS or are dealing with a person who just does not have a clue how regs work. The MK-2 has the same IP (interstage or intermediate pressure) as any other SP reg and will flow more gas than most 2 second stages flowing wide open can and certainly more that 2 hyperventilating divers can....how much more do you need? Sure, some of the other SP first stages can flow more with the ports disconnected but if the second stages are the limiting factor (and they are) what does it matter. Does it really matter a Farri will go faster than a Chevy if the road you are diving on has a 55mph speed limit? Both will go faster than the road will allow. Same thing, the road and the second stages are the limiting factor, not the cars or first stages. Granted the cool factor and bragging rights are better with the Farri and the MK-25 but if you look at what really matters, how long it takes you to get to work and how well they breath, they are the same.

It may well be true that SP will not sell them as separate pieces- they don't want people buying low end (inexpensive) first stages to go with higher end second stages, it cuts profits too much but to say they will not work together is pure BS.

This is true... BS.
According to SP's official manual, the MK2+ has a flow rate of 92 CFM and the G250V's is 57 CFM.

Don't let them scare you away with their techno-babble. The combination is unusual perhaps, not profitable for them for sure.

That being said, it's also true that the usual practice is to sell a higher end 1st stage than the 2nd, because a balanced 1st is better equipped to deliver a constant intermediate pressure (IP) than a balanced 2nd to cope with a declining IP from a non-balanced 1st. In other words, balanced 1st + unbalanced 2nd is potentially better than the other way around, which is your proposed configuration.

I prefer the unbalanced first with a balanced second instead of the other way around. Most balanced seconds have a better design and their work of breathing (WOB) tends to be less. A good balanced second has little trouble dealing with the IP swing in most unbalanced second stages. I ran a test a while back, varying the IP of a reg across a 40 psi range (100 to 140) just to see what happened. My balanced SP G200-B second stage cracking pressure only varied a small amount over the entire range. About 0.5 IWC (inches of water column) across the entire range and more importantly only about 0.25 across the first 20 psi drop, which is somewhere around the IP drop of a good flow by piston (MK-2). Both ways are a trade off but IMO from a performance and cost perspective, the unbalanced first with the balanced second is the better of the 2 ways to go.

 

[Zung]

... I ran a test a while back, varying the IP of a reg across a 40 psi range (100 to 140) just to see what happened. My balanced SP G200-B second stage cracking pressure only varied a small amount over the entire range. About 0.5 IWC (inches of water column) across the entire range and more importantly only about 0.25 across the first 20 psi drop, which is somewhere around the IP drop of a good flow by piston (MK-2). Both ways are a trade off but IMO from a performance and cost perspective, the unbalanced first with the balanced second is the better of the 2 ways to go.

Thanks Herman, that's a valuable experiment you conducted.

While my explanation is OK, I think, from a theoretical point of vue, I agree that a good balanced 2nd pays off better because you can feel the difference immediately. I still remember the "wow" factor I felt some 15-20 years ago when I switched from an AL Supra/XL, a very good reg with a classic downstream second, to the SP MK20/G250.

But then again, there are surely other factors such as the barrel, the moisture, the turbulence, etc... that make the R109/G200B/G250 truely exceptional.

 

[batman diver]

Here a q , how come so many divers like certain older regs , do they not make the newer ones as well or wats up ? One of the 1st things I noticed when I started , and sorry noob q , what's cracking pressure

 

[Zung]

1. Older regs: IMHO, reg technology peaked some 10-20 years ago; since then, most R&D efforts are geared toward reducing cost, therefore lots of plastic parts, ease of service, so still more plastic parts (re.: inside the SP MK20/25 vs the MK5/10), and bling factor: even more plastic parts. That been said, I have both the G250 and the older R109, and I like the G250 better, so far; I also have both the MK20 and the MK10, and I definitely prefer the MK20 because it's a lot easier to service.
2. Cracking effort: when you start sucking on a reg, first nothing happens, then the reg "cracks" open after the vacuum you formed reaches a certain level. That level is expressed in cm or inch of water, usually between 1 and 1.4 inch of water; the lower the better until it starts free flowing.

 

[diver 85]

Let me say this---I brought my Mk10/G200 & my Mk2/R295 to Fiji last week as my 2 regulators......Started with the 'better' Mk10/G200 & just for the heck of it I changed after 3 days of diving to my Mk2/R295 for the last 3 days-----NEVER noticed a difference....never did any 'real' deep dives(ie below 90') but still both were the same to me.............FWIW....


ie-------I love the Mk2/R295

 

[Zung]

I too did an experiment.

Last summer, I did a dive that was predictably boring, so I took both my wife's MK25/G250 and my #2 son's MK20/G250C (Clear) down, initially to make sure I did the servicing right before handing off the gear. Both 1st's are at 131 PSI, the 2nd's have the Venturi set at mid-range, with somewhat initial different cracking effort because the son likes it a bit stiffer.

And the difference between the 2 sets is quite noticeable, even after I equalized the cracking effort with the adjustment knob. Can't say which one is better, but they're different; the wife's maybe a bit smoother, but the son's a bit more "forceful". And I'm talking instantanuous comparison here: a few breaths one, a few breathes the other.

Why is it so I have no idea. Any comments?