Scubapro naming convention?

[Angelo Farina]

I wouldn't agree with this assessment. The MK25 does work ok in very cold water, but it is hardly 'greatly engineered' for cold water. It is not sealed, but there are some coatings and plastic bushings added to reduce or prevent ice build up. Given the fact that a very similar type of regulator, the atomic 1st stage, as well as earlier SP 1st stages (MK5/10) can be fully sealed with either PTFE or silicone grease, the MK25 is comparatively not well designed for cold water. Again, there have been many thousands of successful dives in cold water with the MK25, but if someone is buying a regulator specifically for very cold water, the MK17 is a much better choice, as is any fully sealed 1st stage.

The "modern" strategy for cold water is not anymore to insulate the moving part (piston) from water thanks to a thick layer of silicon grease, as in older Mk5, Mk10 or Atomic.
The strategy employed in the MK25 is opposite: to guarantee good heat exchange beteeen the area where adiabatic expansion is causing cooling with the surrounding water.
In this sense, the MK25 is very well engineered.
Which of the two strategies works better is matter of discussion. But if SP engineers, who previously invented and fully mastered the SPEC approach, decided to abandon it for the new high conductivity approach, I suppose that they had data demonstrating that this new strategy is better.
As said, sealed diaphragms have other nice advantages. But if the concern is just cold water performance, I would not grade the MK17 as definitely better than the MK25.
Being more precise: thermal insulation by means of a chamber filled of silicon is probably advantageous in case the water is really at icing point, and the reg would cause it to solidify even with a moderate air flow.
The thermal conduction approach, instead, is possibly better when the water temperature is at least 1-2 C above the freezing point, and the formation of ice is caused by a significant air flow.
So in the first case the MK17 is better, but in the second case, which possibly is more frequent, the design of the MK25 is better...

 

[Angelo Farina]

To me, the MK25 is not a good idea: most of the water in shore diving around here has silt and mud. Ridiculous design. I have one and I don’t know why I bought it. Should have gone for the MK17.

Yes.
In silty water a sealed reg is always to be preferred...

 

[halocline]

The "modern" strategy for cold water is not anymore to insulate the moving part (piston) from water thanks to a thick layer of silicon grease, as in older Mk5, Mk10 or Atomic.

Oh yes it is, in all environmentally sealed 1st stages, which is what every regulator manufacturer does for cold water use, including SP with the MK17. The MK25 is not designed specifically for cold water; it has a poor basic cold water design (unsealed flow through piston) with some improvements in the coatings, bushings, and fins on the turret. These modifications likely improve the freeze resistance of the MK25, but that doesn't make it ideally engineered for that purpose. It's more of a work-around to make it acceptable in cold water. These parts don't prevent freezing, they are there to prevent ice build up on the piston and spring.

I understand about better heat transfer allowing the water to warm up parts cooled by expanding air. This is especially helpful in 2nd stages, where it is effectively impossible to keep working parts of the regulator dry. But with first stages, there is MUCH more adiabatic cooling, and it is possible to keep these parts dry if you seal the environmental chamber, which is what everyone does for regulators designed specifically for cold water.

I love the SP balanced pistons, they are basically all I use as 1st stages. I'm not arguing that the MK17 is a better 1st stage. But it IS more freeze resistant.

 

[rsingler]

It's funny how little love Sherwood/Genesis gets.
They've been around just as long.
The dry bleed valve design is no weirder than SPEC.
Their Schrader valve design is unique for pistons.

But they just haven't caught on...

 

[ginti]

How do you define cold water? And silty water?

I bought my MK25evo not before making a bit of research. I asked several people, and apparently no one has ever had problems of any sort. I spoke with divers who claimed to have used MK25evo+G260 in water cold up to 4°C (39.2°F) in what they called "very silty water" at depth ranging up to -75m (wreck diving in the UK). The "evo" indicates a new technology to provide same performances of diaphragm reg in terms of cold/silt resistance:
https://ww2.scubapro.com/en-GB/HKG/regulators/products/mk25-evos600.aspx

I never had a problem with this set, and I dive often in 8°C (46.4°F) water, sometimes down to 6°C (42.8°F). Never had any problem with silty water as well. Obviously, the fact that I never had a problem does not mean that other people never had one.

But I still need to hear about a single prolem with this combination (MK25evo+G260). Do you know any aneddoct? I am not provocative, I am seriously asking because I really don't want to have bad surprises while diving)

I try to give a short answer.
- central poppet: this generation started with the mythical Pilot (the regulator which is till now the easiest-breathing device ever built, but it was a nightmare to service and tune). That chrome beauty was soon replaced by plastic clones, such as Air1, and the long D series, culminating with the current D420, which is currently the top unit of the SP line.Expensive units well suited for very deep diving.
3) The G250 and all its variants, obtained on one side by declassing it to versions without effort knob and/or unbalanced, such as the G200, and on the other side improving the original design with many particulars, such as carbon fiber parts, titanium parts, gold-plated parts, and modern variants such as the G250HP and the G250V.
The G250 has been the most succesfull reg ever built, sold in large numbers and being manufactured for more than 30 years. Only recently the latter G250V was replaced by the G260, which is currently the SP reg tailored for usage by commercial and tech divers. This is what I usually recommend to buy to people asking advice on which reg they should purchase. My advice is to buy a MK17 or MK25 first stage and two identical G260 (I hate the idea of a lower performances secondary octo).

Very accurate, as usual Do you know the differences in terms of performances between D420 and G260? What would you reccommend for deep tech dives, possibly in cold and silty water? Thanks!

 

[Angelo Farina]

@ginti, cold water is defined at below 6 C.
See here for techical info coming directly from SP Europe:
SCUBAPRO MK25 Regulator, Considerations for Cold Water Diving | Facebook

Regarding the D420, I have no direct experience on it. It appears that some units are sold without proper tuning, but this reg appears to be much easier to service and tune than its predecessors of the D series.
However I do not think that its superior performances are worth its not-traditional design for people diving at less than 60m in air and less than 120 m with He mixtures.
As 98% of divers do not exceed these limits, I still consider that for them the better 2nd stage is the G250V, or, if unavailable, the unnecessarily slightly more complex G260.
If instead you are among those 2% of divers who still make deep air dives in the range 60-90 meters or deep hypoxic trimix dives below 120m, then the D420 can provide significant advantages reducing the WOB and consequently the CO2 buildup.
Please also evaluate that the depth limits for "deep" air or "deep" trimix I stated above are not generally accepted everywhere: some people consider that "deep air" begins at 50m and "deep trimix" begins at 100m.
The concept is the same, just the thresholds where switching to a D-series unit is recommended are shallower.

 

[BoltSnap]

How do you define cold water? And silty water?

I bought my MK25evo not before making a bit of research. I asked several people, and apparently no one has ever had problems of any sort. I spoke with divers who claimed to have used MK25evo+G260 in water cold up to 4°C (39.2°F) in what they called "very silty water" at depth ranging up to -75m (wreck diving in the UK). The "evo" indicates a new technology to provide same performances of diaphragm reg in terms of cold/silt resistance:
https://ww2.scubapro.com/en-GB/HKG/regulators/products/mk25-evos600.aspx

I never had a problem with this set, and I dive often in 8°C (46.4°F) water, sometimes down to 6°C (42.8°F). Never had any problem with silty water as well. Obviously, the fact that I never had a problem does not mean that other people never had one.

But I still need to hear about a single prolem with this combination (MK25evo+G260). Do you know any aneddoct? I am not provocative, I am seriously asking because I really don't want to have bad surprises while diving)



Very accurate, as usual Do you know the differences in terms of performances between D420 and G260? What would you reccommend for deep tech dives, possibly in cold and silty water? Thanks!

I dove with the SP regulator in 3.3C/38F in New England without any issues whatsoever and have friends who do dive in icy water in the great lakes, New England, etc. (technical diving to great depths) for years and years and use nothing but the MK25 regulator and never had an issue. One has to follow ice diving rules that apply to ALL brands and models of regulators.

Just be aware that here on SB there are many people that talk through their hat based on "theories" they concocted in their heads not based on reality and actual experience.

 

[rsingler]

I never had a problem with this set, and I dive often in 8°C (46.4°F) water, sometimes down to 6°C (42.8°F). Never had any problem with silty water as well...
But I still need to hear about a single prolem with this combination (MK25evo+G260). Do you know any anecdote?

The EVO is too new to show the problems referred to here:

It takes literally years to occur, tho' it can happen faster if a gritty reg is put away wet, the salt crystallizes and then the reg is used again repeatedly. So the EVO hasn't had time to show it yet.

But the problem remains, and coated springs don't eliminate the fundamental issue: an ambient chamber exposed to floating grit which adheres to the film of lube in the crack where the piston head oring meets the body of the regulator.

If you are religious about flushing out your gear you'll be fine for a decade, minimum. That means 95% of divers will have moved on to other regs or other hobbies before the issue shows up. EBay is where you find it.

I've been a piston guy. I'm a sealed reg guy. That means an old SPEC-sealed Mk10 or a new sealed Atomic. I have a new Mk25 EVO that came with my D420 that has never been wet that I have no use for. I'll probably put it up on EBay soon with an A700 that's lying around.

 

[BoltSnap]

The EVO is too new to show the problems referred to here:
View attachment 617448
It takes literally years to occur, tho' it can happen faster if a gritty reg is put away wet, the salt crystallizes and then the reg is used again repeatedly. So the EVO hasn't had time to show it yet.

But the problem remains, and coated springs don't eliminate the fundamental issue: an ambient chamber exposed to floating grit which adheres to the film of lube in the crack where the piston head oring meets the body of the regulator.

If you are religious about flushing out your gear you'll be fine for a decade, minimum. That means 95% of divers will have moved on to other regs or other hobbies before the issue shows up. EBay is where you find it.

I've been a piston guy. I'm a sealed reg guy. That means an old SPEC-sealed Mk10 or a new sealed Atomic. I have a new Mk25 EVO that came with my D420 that has never been wet that I have no use for. I'll probably put it up on EBay soon with an A700 that's lying around.

I am not sure that you will see this issue with a regulator that has been serviced every 2 years by a qualified technician. There maybe other issues with the regulator due to the extreme neglect and abuse of the regulator by the owner/user.

 

[Julius SCHMIDT]

The trick is to keep piston regulators wet!
thereby lubricating the skinny piston to chamber oring to wash away as much silt and dirt and rocks and chrome as possible until you end up sanding off the remaining chrome polish it up and use the reg for another fifty years
with the correct cold breathing protocols