2nd Stage regulators for Doubles

[DA Aquamaster]

There have been some ungodly complicated balanced reg designs over time (features to remove pressure form the seat when the air is off, etc) and there are still a few of them around today - but the S600/S555/G500/G250V/G250HP/G250/G200B are not among them.

In the case of the G200B and S555 the only difference betwene that design and an unbalanced G200 is a poppet with a hole through the middle, a lighter spring and a fixed balance chamber. The poppet has 2 o-rings and only needs 1 so there is 100% redundancy. The spring pressures are actually lighter than in the their unbalanced counterparts (R109, G200, etc) so seat wear is actually reduced.

The G250 and G250V add an adjustment knob with 1 o-ring that only has to resist a maximum of perhaps 20" of water pressure if you inhale really really hard.

The knob on the S600 and G250HP is slightly more complex, but the case o-rings has a redundnat back up and the internal o-ring inside the knob is static and not prone to wear. I have never seen one fail.

Oddly enough I did see a recent failure of an R109 Adjustable (an unbalanced design) where the pad for the spring fractured and jammed the spring in the air barrel causing it to fail to deliver gas. That failure could not have occurred in the Balanced R156 version of that reg.

Unlike the G200, most unbalanced regs are dual adjustment models (separate adjustments for both orifice and lever height). In comparision to an unbalanced dual adjustment reg like the R190/R290/R295/R380/R390 all of the above singel adjustment (one adjustment for both orifice and lever height) models are at least as reliable. There are things that can go wrong in an unbalanced dual adjustment reg that can cause leaks or failure to deliver air that cannot happen in the balanced or unbalanced single adjustment design such as the retaining nut for the lever coming off, the washer fracturing, etc. so one is not really any more failure prone than the other.

In short, you may feel like you are safer with an unbalanced second, but you really are not, you'll just be breathing harder and have a reg with less flow and less working range every time you use it.

 

[DIR-Atlanta]

Are you using MK25s also for all our stage and deco bottles as well? Just curious.

With the exception of a couple of legacy Mk10s (which I just cannot bear to part with), yes I am using Mk25s for everything. Actually two of them started out as Mk20s but have been upgraded. The advantages are that everything is completely interchangeable with everything else, they're very reliable, only one parts kit to worry about, and the hose routing is good (actually optimal, IMO). I don't ever dive in water cold enough to require an environmental seal, so it's the best all-around choice for me.

For my backgas I use an Atomic B1 for the primary, Z1 for the backup. I will probably eventually switch those to Mk25s as well, but I'm in no real hurry to do that.

 

[elan]

Thanks everyone...I was deciding on the notion that the R295 was substantially less likely to fail..I'll definately go with the Mk25, because it supplies enough air for 2 divers, and I supose on 2nd thought...Being a couple thousand feet in a cave and having to swim out, I would want the easier breathing Reg.

My bet is that the advise was to put the unbalanced second stage due to the fact that they are less prone to "opening up" when they are out of mouth. The adjusting knob does not always help.

 

[ivobj]

I use 2 x MK25 and 2 x S600, as already mentioned, you must remember that when donating gas you will be breathing from the backup. If you want to save something use S555 for backup, they are very good as well, balanced, but does not have the adjustment knob, there is a fixed flow, which is more than enough. I use in all my stage bottles MK17 with S555.

 

[rjack321]

With the exception of a couple of legacy Mk10s (which I just cannot bear to part with)

If you want to, let me know. I like them and can't tell them from mk20/25s anyway.

 

[RTodd]

My bet is that the advise was to put the unbalanced second stage due to the fact that they are less prone to "opening up" when they are out of mouth. The adjusting knob does not always help.

Bingo. On a high helium mix at depth, it takes a really crappy reg not to function well. A lower quality second serves as a great backup and delivers plenty of gas. When you factor in how much more likely annoying freeflows are on a scooter dive of significant distance with lots of stages, this is often the winning factor. I used to use the crappiest second I had on my deep cave rig (where freeflow was a bigger issue) and for recreational open water stuff where the length of time on the backup would be minimal and not really under stress. Now, I use either G250s or TX50s on both to keep them consistent. The SPs are slightly more prone to freeflow than the Apex though even when tuned down. The only real situation where the better breathability of a second stage would matter would be cave swim dives or intermediate depth lower HE open water dives.

 

[RTodd]

With the exception of a couple of legacy Mk10s (which I just cannot bear to part with), yes I am using Mk25s for everything. .....

My only remaining Mk10 is one of my O2 regs. They just can't quite seem to duplicate the performance of that reg so I save it for the rare occasion where I will have to spend significant time on it.

 

[rjack321]

Although this discussion has focused on why a high performance 2nd is so great - something I have not found a need for...

Bingo. On a high helium mix at depth, it takes a really crappy reg not to function well. A lower quality second serves as a great backup and delivers plenty of gas. When you factor in how much more likely annoying freeflows are on a scooter dive of significant distance with lots of stages, this is often the winning factor. I used to use the crappiest second I had on my deep cave rig (where freeflow was a bigger issue) and for recreational open water stuff where the length of time on the backup would be minimal and not really under stress. Now, I use either G250s or TX50s on both to keep them consistent. The SPs are slightly more prone to freeflow than the Apex though even when tuned down. The only real situation where the better breathability of a second stage would matter would be cave swim dives or intermediate depth lower HE open water dives.

This is why (to me) a non-adjustable primary like the s550 is not really a great idea. You have to detune your primary or risk losing a bunch of backgas in your armpit while on a stage.

 

[rjack321]

My only remaining Mk10 is one of my O2 regs. They just can't quite seem to duplicate the performance of that reg so I save it for the rare occasion where I will have to spend significant time on it.

Funny, I use a mk2/r190 for O2. Works perfectly fine, easy peasy breathing. At 20ft you'd never know it was an unbalanced first and unbalanced 2nd.

 

[adm3745]

So my smartest options are to get another S600 so that I can have greater control over free flow, or get an unbalanced R295 that I know will free flow much less than say a S555? The reliability factors on the different SP's seem to not be a big deal. Trimix is in my future, and I feel fine breathing my current unbalanced backup at depth. Is the S600 really worth the extra $300 to have for backup if I know that sill in case of an emergency, my 295 does get the job done?