My first mk5 ...

[Angelo Farina]

Ah, okay, that's right that the turret retainer nut had to be changed from brass to SS, but I don't remember that I ever have seen those SS nuts in MK5s (I will check).
I think I remember that that was an issue with the MK20s....

In any case we are talking about very remote risks. I am quite confident that my four old MK5, with their original brass retainers, are indeed "secure enough" for me.
When I dive I am exposing myself to dozens of risks which are probabilistically much more concerning than the risk associated with the swivel turret...
On the other side, if one offers me two vintage 1st stages in similar good conditions, I would prefer a MK9 over a MK5 (and a MK10 over both of them!).
But this is matter of personal preferences.

 

[halocline]

There is one point that might be considered 'safer 'with the MK9/10.
One of the disadvantages of the MK5s was the uneven air output of those 1sts.
While the MK5s delivered at 135bar (ca. 2000psi) 2464 liters/minute (87SCFM), they delivered at 20bars (ca. 300psi) only 1359 liters/minute (48SCFM).
The new MK9/10 design changed that at the same pressures to 2265l/m(80SCFM) and 2067l/m(73SCFM) to almost even.

You're talking about supply pressures, correct? So what you're saying is that the MK5 delivered only 48 CFM with a tank pressure at 300 PSI, as opposed to the MK10 which delivered 73 CFM at the same supply pressure?

If that's the case, then I think you could more easily make a case that the drop in airflow in the MK5 is 'safer' because presumably, there would be a corresponding increase in breathing effort under severe demand, especially with an unbalanced 2nd stage. This could give a diver some warning that he is dangerously low on air.

Then again, think about the numbers here. 48SCFM is still the equivalent of draining an entire AL80 in under 2 minutes. Hardly a restricted airflow.

 

[halocline]

On the other side, if one offers me two vintage 1st stages in similar good conditions, I would prefer a MK9 over a MK5 (and a MK10 over both of them!).
But this is matter of personal preferences.

It's too bad we're on different continents, I'd be happy to trade a MK10 for a late model MK5! I think the shipping would be almost as much as simply buying a new reg, though.

 

[Angelo Farina]

It's too bad we're on different continents, I'd be happy to trade a MK10 for a late model MK5! I think the shipping would be almost as much as simply buying a new reg, though.

Well, I just did a "double swap" of this type with Couv and Lowviz, I gave out my MK15 first version for a mint MK10...
And yes, it costed a fortune in shipping!
But please, can you elaborate why do you repute the MK5 preferable over the MK10?

And yes, I am tempted by your offer, particularly if your MK10 has the rubber SPEC boot (without holes). And if you can throw in another spare SPEC boot for the MK10, the deal is done!

 

[axxel57]

You're talking about supply pressures, correct? So what you're saying is that the MK5 delivered only 48 CFM with a tank pressure at 300 PSI, as opposed to the MK10 which delivered 73 CFM at the same supply pressure?

If that's the case, then I think you could more easily make a case that the drop in airflow in the MK5 is 'safer' because presumably, there would be a corresponding increase in breathing effort under severe demand, especially with an unbalanced 2nd stage. This could give a diver some warning that he is dangerously low on air.

Then again, think about the numbers here. 48SCFM is still the equivalent of draining an entire AL80 in under 2 minutes. Hardly a restricted airflow.

Yes, I'm referring to supply pressure, but I would rather dive a 1st with a stable air flow over the whole dive than getting a warning which I could also have by watching my SPG.
Of course is also 48SCFM not little air, but when I was working on the Maldives, there was still no official depth limit, so we had some petty deep dives also with customers.
In the unprobable case of having a panicking diver low on air to bring to the surface, I would have had no problems, even with quite more than 300psi, to have constant high air output from my 1st.
I agree with you that for a single diver (even hard working in deeper waters) it would not be easy to lower the dynamic IP to a point, where the overall air supply by the 1st stage could lead to a 'corresponding increase in Breathing effort' (since MK5 & MK9/10 are balanced, the supply pressure shouldn't play otherwise really a role in 'normal' conditions), with two divers at one 1st I think that could be different.
With your type of argument maybe we should all dive equipment from the 50' and early 60', because it was not a good idea to make really deep dives, so that equipment was safer'?

 

[halocline]

I’m just wondering what kind of actual dive situation would result in two divers breathing hard at significant depth on a tank with 300 psi. That’s an unplanned emergency or serious negligence. I’m not seeing how increased airflow adds to the safety of such a scenario.

I agree that ideally a first stage provides stable IP and airflow at all supply pressures, and that the MK10 has better airflow characteristics than the MK5. But that has nothing to do with safety.

 

[axxel57]

I’m just wondering what kind of actual dive situation would result in two divers breathing hard at significant depth on a tank with 300 psi. That’s an unplanned emergency or serious negligence. I’m not seeing how increased airflow adds to the safety of such a scenario.

I agree that ideally a first stage provides stable IP and airflow at all supply pressures, and that the MK10 has better airflow characteristics than the MK5. But that has nothing to do with safety.

Ah, well, okay.......

 

[Angelo Farina]

With your type of argument maybe we should all dive equipment from the 50' and early 60', because it was not a good idea to make really deep dives, so that equipment was safer'?

I do not follow you here. I do not know about fifties and sixties. But the equipment I was using in the seventies was definitely safer than most modern equipment.
For start, we all were using double cylinders (10+10 liters), with two independent valves and two independent regulators.
Those regulators were mostly the same MK5+109 I am using today.
Later doubles almost disappeared, and 20 years ago the standard was a single of 15 liters, yet with two separate valves. Definitely less safe.
And nowadays cylinders are just 11 liters and with a single valve, so I am forced to use just one first stage with an octopus.
In my view the systems in use in the seventies were far safer, providing you with a much larger reserve of air and a truly redundant set of two independent regs..

 

[axxel57]

Yes, if the amount of air a diver can use on a dive is the main safety aspect, then you might be right and commercial helmet divers do the safest diving.
For me is the amount of air available on a dive just one aspect of safety between others.
If I dive in 15 feet on a coral bank (as you might have done in your job a couple of times), then a double 10l set probably gives you a larger reserve and one could consider that as more safe.
But what means safety when you have more air as you can spend in a half day underwater?.
I think redundancy is important, for example in cold water with the danger of regulator icing or in really deep diving, but there (at least here in Middle Europe) it is anyway standard.
Even if I follow your arguments, I still have to subtract from the 'win of safety' through more air, the added failure points I'm carrying with me when diving with doubles and double regs.
I think that other aspects have made dive equipment really safer, for example the introduction of the standards of the CE Norms, which swept a lot of lousy equipment from the market in the late 80's and early 90's.
The tests on the ANSTI machines helped to make performances of regulators comparable and mostly better.
Dive Computers and Jackets have also helped to make dives safer and more efficient.
So for me the concentration only on the amount of air supply is a bit questionable.
It is clear that you are a fan of the MK5/10s 1sts and 109er 2nds. So are a lot of us here.
They are classics, undestroyable and timeless.
But SP designed also some other regs, which are at least as classy and technically brilliant as that combo.....

 

[Couv]

@axxel57 I cannot find your MK6 ???