gwolbrink once bubbled...
I am on a new (and green) dive rescue team in South Dakota. 1/3 of the year, the water is covered in ice. Right now I dive a SP mk5 with a 109?? It works great for recreational diving but I think that I need more. Am I right?
I am also from SD and normally dive Pactola which is 150 ft deep and cold with upper 40's being as warm as it ever gets at the bottom in late August.
I currently use a MK 20 D400 and MK 25 D400 and have never had a freeze problem with either of them them. The MK 20/25 cold water freeflow issues are not as simple as it sounds as some freeze and some don't and it could be a combination of breathing styles, second stages used, or various parts issues. The most recent news I have heard is that some of the problem may be due to the o-ring on the piston being too soft. Mine work perfectly but others do not so while the MK 20/25 is an excellent reg, I don't really recommned it until Scubapro resolves the problem. (Part of the development problems may be that Scubapro considers 50 degrees to be cold water. They need to do their testing where I dive.
A Mk 5 109 is a good regulator anyway you cut it. It would work well for cold water as long as the ambient pressure chamber is silicone filled. A SPEC boot helps keep all the silicone in place but is not a have to have item. (I am not sure if even the late production MK 5's were ever provided with a groove for the boot) The Mk 5 was considered a bullet proof high performance design and was cutting edge for years. It was well liked and stayed in production along side the newer Mk 10 for nearly a decade.
I have used various Mk 10 Balanced Adjustables and MK 10 D400's for years, and my son and spouse still use them in cold water. They are utterly reliable in cold water when used with a silicone filled ambient pressure chamber.
The design differences between the later production Mk 5 with multiple ports and the MK 10 are pretty minimal. There are some minor internal changes and the MK 10 has a rotating turrent for the LP ports. The MK 9 was sort of a go between as it had the Mk 10 internal changes but no turret, which was viewed with some degree of distrust as an additional failure point when the Mk 10 was introduced.
The Balanced Adjustable second stage shares the same internal parts as the G250 and gives identical breathing performance. The only difference being the lack of an adjustable flow vane and the use of a brass case on the Balanced Adjustable as opposed to the phenolic case on the G250. The metal case offers better heat transfer charactorisitics and is actually better suited to cold water divng. The D400 is also an excellent cold water reg due to it's internal design and its lack of susceptibility to freezing.
If I were you I would not sweat using a MK 5 and if I changed at all it would be to go to a Mk 10 Balanced Adjustable or MK 10 D400. They can be had for around $150-$200 respectively on E-bay. Getting them serviced is not a problem in SD whereas getting an Apeks serviced could be an issue.
Both Skin and Scuba Oahe and Donovan's tend to be a little pricey on service. I found Scuba Supply in Rapid City to be much more reasonable for annual service charges. Bill retired and they have just been been bought out by Mick's Scuba in Rapid City but the service and low service rates will remain the same and in fact will most likely be even more reasonable.
A Mk 15 with a SPEC boot is also an option. Originally it had part of the current TIS system used on the MK 20 and 25 combined with a silicone filled ambient pressure chamber and a SPEC boot. Finding one in this original condition is hard though as SP stopped recommending the ambient pressure chambers be silicone filled and I don't think the SPEC boots are available any longer. A SPEC booted Mk 15 offers all the cold water advantages of the Mk 10 with the performance of the Mk 20 and Mk 25.
The major difference between the Mk 15 and the Mk 20 is that the Mk 20 has a few internal changes to make it easier to service. The Mk 25 offers an external intermediate pressure adjustment but offers no performance advantage over the Mk 20.
The Mk 16 offers a sealed ambient pressure chamber and would work very well in cold water bt in my opinion it does not offer the perfromance, reliability or ease of maintainence of a piston reg. (an opinion that has in the past bene the basis of much debate in this forum.)
