MK25 LP ports?

[Dan Gibson]

What was that ridiculous number of divers breathing off a single SP first stage? That alone ought to put to rest the 20% more flow from the bottom port.

The Mk 25 flows such an excess of air from any of it's ports that it is truly a 20% increase that you don't need.

 

[DA Aquamaster]

I think it was something like 20 or 25.

 

[WarmWaterDiver]

More than that according to Scubapro UK

http://www.scubapro.co.uk/pdfs/Scubapro75.pdf

Why would this "put to rest 20% more flow from the bottom port"? Are the Scubapro manuals in error on this? Is there an errata sheet showing measurements inaccurately performed?

 

[archman]

http://www.scubapro.co.uk/pdfs/Scubapro75.pdf

That's messed up. 75 divers breathing off one MK25. I particularly liked this line...

Due to the extremely high flow, ice formed all over the cylinder
valve, 1st stage and even on the low pressure hoses. The Mk25
however didn’t stop delivering air and things began to settle down
nicely.

 

[jumbo]

DA and cres-

Very true, but still a cool stat to throw out. Any one of the LP ports on the Mk25 provide more air that ten divers could use. When going through the training seminar I think the tech said that in Africa some 70 divers breathed off one Mk25.

JUMBO

 

[Vie]

A group pulled a similar stunt in South Africa with a Mares MR22:

http://www.deeptec.co.za/page3.HTM

Not exactly sure what this proves. I guess publicity is always good...?

 

[peterbkk]

The 5th port could be used for blowing up balloons for underwater parties...

 

[DA Aquamaster]

The difference is in the depths and temps where the test occurs. Being 5 ft deep in an 80 degree pool does not mean much. It's also a bit like the "20% more flow from the top LP port" comment - at some point how many more divers it will support is irrellevant.

Tests like that are also misleading as the limiting factor in the real world is the second stage. You can only flow so much air at a given pressure through an orifice of a given size so even a very high performance second stage will have a limit of about 65 SCFM.

I suppose it's comforting that the 300 SCFM flow rate of the Mk 25 would enable me to continue to breathe while 4 other buddies depress the purge valves on 4 other second stages attached to my Mk 25 (I suspect the ability to actually do this is the real reason for the 5th LP port) but at 300 SCFM, the comfort would be short lived even with doubles.

 

[Dan Gibson]

I'm referring to the fact at some point it becomes pointless, not the fact that it actually gives you 20% more.

Why would this "put to rest 20% more flow from the bottom port"? Are the Scubapro manuals in error on this? Is there an errata sheet showing measurements inaccurately performed?

 

[WarmWaterDiver]

Well, it should definitely prove the calculations I did on potential 100% adiabatic temperature drop are quite accurate - icy externals on hoses in an 80 degree pool, with hoses that are poor heat transfer materials, are excellent empirical proof, especially when latent heat as well as sensible heat are considered for water to turn to ice, and that properly dry breathing gas is essential to prevent internal first stage icing. If the gas supply for these tests had any appreciable moisture content, the experiment results would never have been achieved.

Anyone who 'derives' a lower 100% adiabatic potential temperature drop has messed up their math somewhere.