Piston vs. Diaphragm

[devjr]

If you look at the "Testers' Choice" section under "what needs improvement", you may note that the discussion deals entirely with second stages. There is a reason for this. Discrepancies which can be detected by laboratory tests and in water tests are identified as problems with the second stages.

Variations in performance of individual Micras, if they exist in an objective sense, could probably be traced to variations in state of tune of these rather sensitive devices.

 

[devjr]

Netdoc, after reading further, I see some comments in Rodales(14 budget regs) which could make a case for your comment concerning the disparity in test results between the Cousteau/Micra and the Titan/Micra.

Rodales says that the Cousteau first stage employs a "turbo assist" which adds to stability of the Cousteau second stage. It does this by decreasing the overpressure or positive pressure boost at great depths, increasing overall stability. Since the Titan/Micra combo lost points compared to the Cousteau/Micra, specifically on overpressure breathing, one could infer that the first stage also is crucial to the precise performance of the Micra second stage in this regard.

Again, since the Micra lost a tiny bit of ground when tested with the Titan 1st stage and since the drop in performance rating was due to a slight overpressure breathing effect, the first stage theory looks sound. This being in light of the earlier articles which stated that the another reg's excellent control of overpressure was due to the Cousteau 1st stage and its "turbo" feature.

Now, it's incumbent on "somebody" to look into the Titan performance stats more closely. Does it or does it not have turbo assist? I don't think so.

In any case, the differences seem minor but Rodales is a bug on the subject of positive pressure breathing. The earlier tests were based on Europe's CE standard for cutoff of positive pressure. I originally thought that the latest test might have used a different standard but I see no indication that they did. So, you were probably right, the differences could indeed be due to different first stages.

 

[The Chairman]

Thanks Devjr,

Its good to know WHY there is a difference, almost as much as knowing that there is a difference. I have put one of my micra second stages on my son's Titan and will do a side by side this weekend. The only variable will be the tank, as my one Micra set up is DIN and the other (as well as the Titan) is a yoke. So one tank will be a 120cfid @ 3500psi and the other will a 80cfid @ 3000psi. I don't believe that will make much difference though... I plan to take both bottles down together, so I can breathe one and then the other. My target depth is only @70fsw, so it won't be too critical of a test.

 

[wheezy]

Just wondering... I'm being more open minded here and looking at other options for my new reg (which I've put more research into than when I bought my car)

Wondering what the benefits and negatives of each are. Specifically looking at the ScubaPro line.. Mark 20 or the Mark 18

I dive mostly from the beach in Laguna.. lots of sand which is one of the main reasons I am considering the APEKS as well.

Any input is appreciated??? Mario??

Thanks guys/gals

 

[wheezy]

Are you guys telling me (by not telling me) that NOOO ONE knows the difference between a Piston system and a Diaphram system????

OkeyDokey Then....

 

[The Chairman]

Hey wheezy,

Well to make it simple... Piston style regulators are very dependable and really need very little to make them environmentally sealed. They do have some openings to the water (including sand) but most people don't worry about these. The draw back, is that they are hard to adjust in the field, especially if the seat develops a set and puts the intermediate pressure off.

On the other hand, diaphragm style regulators are still dependable, and most can be environmentally sealed with a kit. This will keep sand and other obnoxious crapola out of the spring poriton of the regulator. In contrast, these are very easy to adjust in the field (a screwdriver and a guage) and in my mind are far more forgiving! All of the diaphragm models I have seen have been balanced, while it is not neccesarily as true for the piston styles.

There have been debates as to which one is "more high performance", but these really boil down to personal preference. Me, I generally prefer the diaphragm, and the Cousteau in particular.

:tease:

 

[Green_Manelishi]

Piston regs CAN be 'enviromentally sealed' if that is
important to you.

Some guys swear by diaphragm regs for use in extreme
diving because they are *less likely* to fail if the water
is dirty or cold.

 

[scuba_adventurer]

Those innovators at SCUBAPRO have done it again.

The brand spankin' new MK 25 is a piston regulator with field adjustable intermediate pressure (you use an allen wrench that is supplied with the reg). It is basically a Mk20 with that addition. They look identical. The draw back, as you know with SP, will be price. I do not know yet what the prices will be on the Titanium Alloy and Brass Model, but the Titanium that I ordered will retail for $1500. That is a huge chunk of change.

 

[turnerjd]

As a big Apeks fan, I jumped last week at the chance to compare the Scubapro and the Apeks at depth (48m, 158 ft)

Here are my observations (TX40 Vs MK20/600) - note the top of the line Scobapro vs the lower-mid-range Apeks - the MK25 hasn't made it's way here yet.

Comfort - I am used to the Apeks, and found this more comfortable, although possibly a bit heavier than the scubapro. The scubapro (partly due to habitude I suspect) didn't feel quite right

Bubbles - no interference from either

Ease of use - both perfect - no problems using / finding purge button etc..

Feel - the Scubopro at the surface feels smoother, you are less aware of it starting to give you air, at depth, (and this is just my impression - I was probably narked off my face!!) the point at which the valve opened seemed to move (ie irregular cracking point) - The apeks is slightly less 'smooth' but has a very sure breathing action, you know exactly what the airflow will start, and this doesn't change with depth.

Reliability - from trying the two out side by side, there is not much I can say, however, general eperience in the UK would lead me towards the Apeks being the more reliable, however, this could be my bias showing through.

Conclusion - They both worked great, with no problems in either, however, the 'feel' of the scubapro changed at depth, and it inspired less confidence than my old TX40. I don't have a TX100 so I can't compare it with that.

As for Piston Vs Diaphragm, I don't think that there is much to say. Both nowerdays are good reliable systems. The best is to try and then buy one you like / inspires the most confidence, irrespective of make / type. - If you are diving cold or poluted, as mario sais, go with the sealed Apeks. Scubapro have a bizarre idea about cold water systems (see my other posts on this topic!) and personally I think that they are off on this one. A good look round coldwater divers will soon show what is the preference!

HTH

Jon T

 

[turnerjd]

Diving!

Work pressure recently, combined with a weeks diving has kept me quiet over the last month or so, but I am now back......

Don't expect to hear too much from me as I have too much work to catch up on...... I only took a week's holiday and the backlog is terrible!

Jon T

PS, If I get a chance to sit down for 1/2 an hour or so I will try and write a trip report, but don't count on it :-(