SCUBA Pro G250 vs. S600

[Luis H]

Awap
You need to start playing with some double hose regulators (preferably a Royal Aqua Master). Then you will see what a seriously large diaphragm has in mechanical advantage. No real need for all this fine tuning, but you can still fine tune if wanted.


Regulators are not built like Swiss watches, there are many small variables form any two units of the exact same model. The variables are most likely worse with molded plastic parts and the thermal expansion of plastics.

Part of a good engineering design is when a piece of equipment can operate at peak performance without depending on tight tolerances and super fine tuning. That is were the brute force of the large mechanical advantage in a large diaphragm shines above other designs. Obviously there are many different ways of accomplishing a similar goal.

Here are some numbers of diaphragm applied forces for three different diaphragm diameters.
Using a 1 inWC suction
Scubapro 109, diaphragm working diameter = 2.5 in, force = 0.18 Lb
New Mistral DH, diaphragm working diameter = 2.375 in, force = 0.16 Lb
Royal Aqua Master, diaphragm working diameter = 4.2 in, force = 0.5 Lb

I haven't bothered measuring many other regulators, but many are in a similar range. The math is very easy, and it is obvious that the area and therefore the force are a function of the diameter square.


Awap, you can often get a Magnehelic for around $20 on eBay. I have bought a few for myself and even for work. They are very accurate and tend to be much easier to use and read than a manometer.


Edit:
Corrected a spelling error.

 

[DA Aquamaster]

+ 1 with that Luis said. It is sometimes hard to compare one model to another. I service a lot of regs and I see some R109's and R156's that are superb regs and I see others that are just not so hot. In some cases you end up having to swap springs and parts to get the various tolerances to all start working in a positive direction. (This is not as big an issue with the R109/R156, but is often a huge issue with the R190 - as they range anywhere from great breathing regs to total dogs.) Now and then I see a reg that I quite frankly recommend be pulled from service as parts repalcement is just not enough to get it up to speed.

I have encountered similar problems with the later production (post 1993) D400 where performance varied a lot more than with the D300/D350 or early D400. With the poor performers, you have to replace the late prodcution orifices and levers with earlier parts to get excellent performance.

The same holds true with the S600 as they do vary more than I'd like to see. I agree with Luis that the tolerances on plastic parts are often problematic and while nearly all S600 can be made to breathe within the liberal production specs for them, not all of them can be tuned to provide exceptional breathing performance without mixing and matching parts.

It is much like building a National Match M-14 where the armorer must have certain major parts that fall within exact tolerances and then a whole bunch of parts from which to select the remaining parts that have very specific tolerances in relation to each other.

 

[rstofer]

It is much like building a National Match M-14 where the armorer must have certain major parts that fall within exact tolerances and then a whole bunch of parts from which to select the remaining parts that have very specific tolerances in relation to each other.

I love the M-14. I have one of the M-1A versions and it is phenomenal out to 800 yards or so. Still, it won't keep up with my Steyer SSG... Two hundred meters, 5 shots covered by a dime.

Back to regulators: I am planning to buy just one SP regulator and I want it to last for a very long time. I don't know how deep I'm going to dive - let's just say really, really deep - maybe 300 feet (I'm not really going to do this, I just want the regulator that can do it). I don't know how cold but let's just say very cold - 30 deg F cold. Plus, I want to dive in the tropics at 30' (my favorite) wearing a T shirt.

Is the Mk-17/G250V that regulator? If not, what is? I am simply looking for the absolute best, most versatile, regulator that SP makes. If that regulator is an older unit that's not in production, what are the possibilities for parts over a very long time?

What should I use for the octo? Same as the primary?

This reg isn't for me. I'm going to stay with my Omega II's. But sooner or later, my grandson will be due for an upgrade and I want it to last for his lifetime regardless of where he chooses to dive.

I hesitate to say that cost isn't an issue but when you think of the long haul, first cost isn't a big deal.

Richard

 

[DA Aquamaster]

I think the Mk 17 G250 is the best reg Scubapro makes.

It is true that the Mk 25 has a lot more flow rate (300 SCFM compared to 177 SCFM) but that is not significant. What matters is that the Mk 17 has more than the 120 or so SCFM that is considered the minium for deep air or really deep trimix technical diving. Helium mizes flow better through any regulator, so at depths where flow rate might start to be an issue with air, you have already been on a helium mix for a hundred feet.

Realistically, not many techncial divers goe below 300 ft on OC and very few go below 350 so there just is not a need for a first stage that will flow 300 SCFM. A very high performance second stage will only flow 65-70 SCFM and the average tank valve or manifold will not flow 300 SCFM anyway. So the Mk 25 is overkill.

The Mk 25 also is prone to freeze flowing in water colder than about 45 degrees so it is not a good choice for very cold water.

The same thing applies to the S600. The pastic parts reduce heat transfer adn do not recycle moisture as effectively so it is als prone to freexe ups and produces more drymouth on long dives. The metal air barrel and splined inlet fitting nut and adjustment knob on the G250V are all very nice to have.