scubapro first stage differences?

[DA Aquamaster]

SP used to publish flow rates on all their regs in their catalogs for comparision purposes. From memory, the early 80's vintage Mk 5 and Mk 10 performed almost identically at high supply pressures (3000 psi) at about 110 - 115 SCFM. At low supply pressures (300 psi) the Mk 10's flow rate was only slightly lower than at high supply pressures but the Mk 5 was down to around 65 SCFM.

On the other hand, the Mk 5 had a larger diameter piston head than the MK 10 and in my opinion had slightly better intermediate pressure stability and better responsiveness. SP apparently thought so as well, as they returned to the larger diameter piston on the MK15/20/25.

 

[oversea]

There are several factors that contribute to MK 25 freezeups including intermediate pressure (lower IP around 120-125 is preferred), tank service pressure (lower is better), SAC rate, and cold water technique (not inhaling and inflating dry suit at the same time, not testing reg on the surface, etc.).

Just one of those factors can make a difference. I and an equally cold water savvy and low SAC rated buddy did 5 dives with Mk 25's in 35 degree water on the same weekend. He froze up on 4 of the 5 dives while I had no problems. The only difference was that he was using 3000 psi tanks and I had 2400 psi steel tanks. He switched to a MK 16 first stage and has not had a problem since.

Both the Mk 16 and Mk 2 do exceptionally well in cold water and divers around here frequently use them ice diving. Scubpro has developed a fully sealed diaphragm first stage, the Mk 17, probably in response to divers who think a fully sealed first stage is important. I am waiting until I see one and dive one to decide if it is an improvement over the Mk 16. On the one hand the Mk 16 has a proven record of cold water performance and is a sure thing. On the other hand, the Mk 17 looks very good on paper and the fully sealed environmental chamber is a theoretical advantage, but the ultimate question will be how prone that seal is to failure over the course of a few hundred dives.

A Mk 16/R390 makes sense as a backup. The R390 is a downstream second stage design and is very simple and reliable, making it a good choice for that application.

Thank you for the information. Would you happen to know the retail cost of an MK16 first stage by itself?

 

[DA Aquamaster]

The MSRP should be around $185 for a Mk 16 first stage only and US SP dealers can discount that 10%, so your cost should be about $167-170.

 

[Wayward Son]

That's a considerable difference in flow between my old Mk5 and even a Mk16. Dunno what it turns out to actually feel like for a recreational diver, mine seems to breath fine even when low on air.

Still, the day will come when I'll replace it. Possibly when I set up a pony rig, I may buy a new primary reg & use this one on the pony.

The budget being tight, when I bought my wife's gear this winter I got her a Mk2/190, she likes it so far. It seems to breath pretty good, and is what my LDS uses for their rental & class rigs.

 

[Life-Is-Good-Diver]

I Just ordered from LP the Mk25 first stage with the S600 second stage. My wife has the SP S550 , and like's it alot. I went with the S600 because i know so many people that use that reg and are very happy with it. One Q i have from being a
Ex-Atomic M-1 diver, how does the ScubaPro S600 and Mk25 compare to the Atomic line, in breathing comparison's at depth?

 

[DA Aquamaster]

That's a considerable difference in flow between my old Mk5 and even a Mk16. Dunno what it turns out to actually feel like for a recreational diver, mine seems to breath fine even when low on air.

A high performance second stage will only flow about 65 SCFM, so even the Mk 5's performance at 300 psi should be enough.

One area where this 1rst/2nd stage comparison does not always hold true is if the first stage has a slow response time that results in a large drop in IP at low tank pressures. In this case, the larger piston head of the Mk 5 (in my opinion) conveys an advantage in response time, flow rate and perceived breathing effort that is not reflected in the raw performance numbers. It is still, by any standard, an excellent design.

 

[mwpowell]

I have a MK2 that I want to convert from yoke to DIN. LP sells a DIN conversion kit, but it says it is for MK16, MK18, MK20, and MK25. Will this kit also work for the MK2?

http://www.leisurepro.com/Prod/Item...Context_954/Sort_Stock/DescSort_0/SCPDC3.html



Thanks,

Mike

 

[cerich]

The Mk 16 has a flow rate of about 175 SCFM while the Mk 25 has a flow rate of 300 SCFM. So the Mk 25 has almost twice the performance of the Mk 16. But I'd challenge any diver to tell the difference between a Mk 16 and Mk 25 in a blind test.

Sounds like you also attended a scubapro tech course.

Do me a favor. Grab a alum 80, take outside get hearing protection. Open valve all the way. How long does it take to empty? More than a min.... YES! The dang valve doen't flow gas that quick.

SP are full of it with their calculations of "flow". That being said the MK 25 is one heck of a good reg.

 

[DA Aquamaster]

The Mk 16 has a flow rate of about 175 SCFM while the Mk 25 has a flow rate of 300 SCFM. So the Mk 25 has almost twice the performance of the Mk 16. But I'd challenge any diver to tell the difference between a Mk 16 and Mk 25 in a blind test.

Sounds like you also attended a scubapro tech course.

Do me a favor. Grab a alum 80, take outside get hearing protection. Open valve all the way. How long does it take to empty? More than a min.... YES! The dang valve doen't flow gas that quick.

Two problems with the draining the 80 experiment though is that the supply pressure constantly falls and that the pressure drop occurs in the flow passage of the valve instead of past it as would occur if it is attached to a regulator. I'd love to see how SP actually tests their first stage flow rates. None the less I agree completely that the valve will become a limiting factor in terms of flow rate in most cases long before a high performance regulator will.

When you consider that even the highest performance second stage around will not flow more than 65-70 SCFM it becomes clear that 300 SCFM is massive overkill. If you figure the worst case of 2 divers inhaling very hard and simulaneously at depth, which even then would not push a 65 -70 scfm second stage to its limit, 140 SCFM would obviously be more than enough to supply both second stages.

 

[Kupu]

I have had my mk16/s550 for 2 years/180 dives and have no complaints regarding the breathing performance of the 1st stage under stress and depths up to 52 meters, I now trust it to perform as needed. I have no experince with the mk 25.

I cannot resist thanking DA Aquamaster for his informative posts...