Mk5 possible devil spring?

[John C. Ratliff]

You should take a Scubapro regulator(s) and then afix them to identical tanks at exactly the same pressure, one with a hose on the top port and one with the hose on a side port. Turn the tanks full on and then time the bleed down. Spoiler alert, it will be hardly any different. And while on the subject, I do not see any significant difference in IP drop between a side port and top port.

I have also run three IP gages on a first stage, a Mk 10. One on the turret side port, one inline with the hose at the first stage and a third in line at the second stage. Spoiler alert, the longer the hose the more the drop or Delta between the gages. And, IMO, the Delta is not significant in use with a properly tuned first stage, short or long hose.

The top port is a good thing in that it allows options for hose routing, especially for twin tanks but increased flow is minimal.

Nemrod, that is not a good “test” of the performance of the first stage. The change which added the top port occurred when the U.S. Navy Experimental Diving Unit tested two different Scubapro first stages (Mk 5 against I think the Mk 2) and found the less expensive one performed better at depth. The Mk 2, if my memory is correct, had only the port on top, but out-performed its more expensive brother.

SeaRat

 

[Nemrod]

Nemrod, that is not a good “test” of the performance of the first stage. The change which added the top port occurred when the U.S. Navy Experimental Diving Unit tested two different Scubapro first stages (Mk 5 against I think the Mk 2) and found the less expensive one performed better at depth. The Mk 2, if my memory is correct, had only the port on top, but out-performed its more expensive brother.

SeaRat

Actually it is a good test. Just time them yourself, from 3000 to 300 psi. Do not worry about what the Navy did, do it for yourself. And then consider that only a few humans, elite athletes, are capable of ventilating at even 8 cfm. You will see an 80 cf empty in a matter of a few minutes through either top or side of turret port, way more volume than a human can use or a second stage could deliver. Can you, with a second stage (in your mouth), empty a 80 cf tank in ten minutes?

A Mk 2 with a port on top? The Mk 2 does not have a so called high flow port.

The current Mk 2 Evo, unbalanced, is rated at 106 cfm @3000 psi inlet pressure, The cfm will go down as the IP drops but should remain above 90 cfm. I have not seen a graph of volume vs inlet pressure and am not going to waste the air and ears to make one for the Mk2. A Scubapro Mk 25 Evo is rated at greater than 300 cfm and compare that to a Conshelf/Titan/Core?helix/Legend at around 53 cfm. All of these provide multiples of the human required ventilation volume of air. Even at 50 cfm you will empty a 80 cf cylinder in under two minutes! Whatever the manufacturers are doing to get such numbers is not via a scuba tank, they have an unrestricted supply air source, not a scuba cylinder.

High flow port or not a high flow port, the human at the end of the chain is unlikely to note a difference at their 1 cf per minute ventilation.

 

[John C. Ratliff]

If you would like, take a look at the U.S. Navy EDU’s letter/report on the Mark V verses the Mark I (my mistake, it wasn’t the Mark 2) from 1970. This has no relationship to today’s regulators, but is why the fifth port was put on the Mark V.

NEDU Eval of Scubapro Mk I and Mk V regulators, 29 Dec. 1970

Did you ever wonder how the Scubapro first stages got that low pressure (LP) line out of the end of the first stage? Well, that happened because the Navy Experimental Diving Unit (NEDU) in 1970 evaluated the Scubapro Mark I against the Mark V, and found that the Mark I out-performed the Mark V...

scubaboard.com

SeaRat

 

[Nemrod]

If you would like, take a look at the U.S. Navy EDU’s letter/report on the Mark V verses the Mark I (my mistake, it wasn’t the Mark 2) from 1970. This has no relationship to today’s regulators, but is why the fifth port was put on the Mark V.

NEDU Eval of Scubapro Mk I and Mk V regulators, 29 Dec. 1970

Did you ever wonder how the Scubapro first stages got that low pressure (LP) line out of the end of the first stage? Well, that happened because the Navy Experimental Diving Unit (NEDU) in 1970 evaluated the Scubapro Mark I against the Mark V, and found that the Mark I out-performed the Mark V...

scubaboard.com

SeaRat

Again, high flow port or no high flow port, any port will deliver far more volume than a diver needs. The difference is minimal when compared to the receiving human demand. You will not notice a difference in air delivery because any of the ports have more capacity than is needed at sport diving depths.

The attachment is the old Navy report, there is a typo in Item 5. And then there is Item 7, like, really, turn the knob all the way in? I would not draw the conclusions that you have from this antique report. The results in the report are within the range of tuning differences between the regulators and a sample of one each is hardly statistically relevant. Reports and results like these did do something good for us all, they brought attention to the often ridiculously small exhaust valves and restrictive exhaust tees of the time. Kind of like putting a 4-barrel carb and manifold on a V8 and then choking the exhaust system down, yeah, Good on the Navy, pack those suckers up and send them back to Scubapro! And USD/AL was worse with an exhaust valve on the 1085 hardly bigger than a dime.

If you can tell the difference in deliverable volume between the turret top port or side port of a Mk 5 or Mk 25 at twenty feet deep in the Clakumus River then you are one hell of a souped up septuagenarian because this septuagenarian cannot at 120 feet. My breathing anxiety issues are all about being 70 years old, not which port my hose is connected to.

 

[MARK74]

Antes de cambiar el resorte, debe medirlo con cuidado. Podría terminar con una IP aún más baja, si usa un resorte de otro MK5 usado ...
Por supuesto, con una cantidad adecuada de cuñas, siempre logré usar cualquier resorte, si no estaba dañado por corrosión o mal manejo.
Nunca propuse esta teoría de que hay "manantiales del diablo", que parecen intactos pero funcionan de manera extraña.

The mk5 that my friend gave me for spare parts never touched water, he had a dive shop where I worked in 1989. Given the delay in receiving spare parts, he left this for parts for his clients, it is missing the turret, the yoke and something else, but it retains the main body, piston and spring. But as I said at the moment I am not going to change anything, until I give it time, I have 20 1@s stages and this is a collection, I just like that all my things work perfectly or close to it. Thanks to all who have participated.

 

[John C. Ratliff]

Again, high flow port or no high flow port, any port will deliver far more volume than a diver needs. The difference is minimal when compared to the receiving human demand. You will not notice a difference in air delivery because any of the ports have more capacity than is needed at sport diving depths.

The attachment is the old Navy report, there is a typo in Item 5. And then there is Item 7, like, really, turn the knob all the way in? I would not draw the conclusions that you have from this antique report. The results in the report are within the range of tuning differences between the regulators and a sample of one each is hardly statistically relevant. Reports and results like these did do something good for us all, they brought attention to the often ridiculously small exhaust valves and restrictive exhaust tees of the time. Kind of like putting a 4-barrel carb and manifold on a V8 and then choking the exhaust system down, yeah, Good on the Navy, pack those suckers up and send them back to Scubapro! And USD/AL was worse with an exhaust valve on the 1085 hardly bigger than a dime.

If you can tell the difference in deliverable volume between the turret top port or side port of a Mk 5 or Mk 25 at twenty feet deep in the Clakumus River then you are one hell of a souped up septuagenarian because this septuagenarian cannot at 120 feet. My breathing anxiety issues are all about being 70 years old, not which port my hose is connected to.

Nemrod,

You have mistaken something here. I use both the side port and the end port on my Mark 5, and do it sometimes with a A.I.R. I second stage, and sometimes with a Pilot second stage. No, I cannot tell the difference when swimming in heavy current in the Clackamas River at 23 feet depth. But that’s not the point.

Scubapro took that Navy finding, and made the extra port on the top. That was their finding, when the Mark I out-performed their Mark 5. That’s the history I was trying to tell. Now, at depth, it could be that there would be less IP drop with the top port than with the side ports, due to air density and turbulence. That is speculation on my part. But there was a reason Scubapro put that top port on, and from what I’ve been told, it has to do with the things I have talked about.

SeaRat

 

[Angelo Farina]

Scubapro took that Navy finding, and made the extra port on the top. That was their finding, when the Mark I out-performed their Mark 5. That’s the history I was trying to tell.

I confirm this story. At the time I was in strict contact with SP Italian factory and they provided the exact same explanation to their commercial partners and shops.
Hose routing was not a concern at the time.
It must also be said that this "problem" of limited air flow from the MK5 only appeared with the Pilot, the only second stage ever built capable of exceeding the air flow produced by a standard MK5.
Of course this was a problem only for "deep air" dives: the Pilot was being promoted for being used at depths below 70m...
This is considered insane nowadays, but it was normal practice for coral hunters in Sardinia, who routinely were diving to 100 meters in air.
They did buy a number of Pilots!
Initially the solution suggested by Scubapro was to connect two hoses to the Pilot, getting air from both first stages mounted on the twin tank.
A friend of mine was using this setup (he was, and actually still is, a deep air diver).
The top port on the MK5 allowed to feed the Pilot to its max flow with a single reg.
But when the 5th port was introduced (1980), the Pilot had already been replaced by the much simpler AIR-1...
So, if you do not own a fully operational Pilot, and you do not use it below 70m in air, the hi-flow port of the MK5 does not give any measurable benefit.

 

[Nemrod]

Nemrod,

You have mistaken something here. I use both the side port and the end port on my Mark 5, and do it sometimes with a A.I.R. I second stage, and sometimes with a Pilot second stage. No, I cannot tell the difference when swimming in heavy current in the Clackamas River at 23 feet depth. But that’s not the point.

Scubapro took that Navy finding, and made the extra port on the top. That was their finding, when the Mark I out-performed their Mark 5. That’s the history I was trying to tell. Now, at depth, it could be that there would be less IP drop with the top port than with the side ports, due to air density and turbulence. That is speculation on my part. But there was a reason Scubapro put that top port on, and from what I’ve been told, it has to do with the things I have talked about.

SeaRat

LOL, whatever, not worth arguing. I was really upset when I calculated there was no Easter Bunny or Santa, imagination is a powerful thing .

Mr. John, leave no doubt, you still are the MAN!

One thing, well, actually there are so many things, but as I said, not worth arguing, but, did they swap the first and second stages on those two units? Basic trouble shooting 101 kinda stuff. Just curious because I do not see that they did.

 

[John C. Ratliff]

Nemrod,

My understanding is that the U.S. Navy Experimental Diving Unit never swapped second stages on any regulator tested (regardless of manufacturer). They would take regulators either sent to them, or purchased by them, and test them as they were received. The Navy also did not like diver-adjustable breathing second stages, as they felt that the Navy divers might inadvertently (or purposely), adjust the regulator inappropriately for their needs, which is why they did not approve the Scubapro regulators with the 109 adjustable second stage.

These tests also pointed out, as did you, the need for increased diameter for the exhausts. This was across the board for manufacturers. I know this caused U.S. Divers Company to increase the size of their Calypso’s exhaust, that AMF Voit did so with their MR-12 (first single hose to gain U.S. Navy approval, I believe), and Scubapro with their enlarged exhaust for their 109 second stages.

The U.S. Air Force simply ignored these findings, and we had purchased the first, second and third generations of the Calypso for our parascuba jumping for NASA and all our water rescue activities.

By the way, I was simply trying to tell the story of that fifth port, not make points. ‘Approciate your comments though.

Angelo,

Thanks for that follow-up comment, as that information is generally not recognized. The Pilot is about the best second stage ever developed, and knowing that Scubapro was promoting it with two first stages before the fifth port came out shows that they were interested in that problem of deep diving on air. I have dived that combo, and it makes for a very interesting variation to the “two hose regulator” concept. The interesting thing is that the AIR-1 second stage initially was to be used with Pilot internals, and actually they can be interchanged. This is according to the designer of the Pilot, Tony Christianson.

SeaRat

 

[John C. Ratliff]

On November 1, 2013 I downloaded several images of the U.S. Navy EDU's study of the Mark 5/AIR-1 combination, using both the 4-port and 5-port (with the LP hose to the AIR-1 second stage on the top port) regulators. Unfortunately, I did not download the entire NEDU report, as I thought I'd be able to access it through the Rubicon Research Repository website (no longer on-line). Note the difference in work of breathing and pressure drop between the two regulators at very high respiratory rates and deep depths.

SeaRat