MK20 -How cold is too cold?

During periods of strong upwelling I occasionally encounter sea water temperatures of 38'F at depth. Temperatures are more typically in the 40-50 range, with air temps in the 60's. I recently heard a report about a second stage free flow causing a first stage freeze up at similar temperatures.

Would anyone feel they need a sealed diaphragm like an MK17 for 38'F water or is the MK20 just fine?

What do people consider the cut off for salt vs. fresh water?

Opinions?

Thx.

RT

It depends. I have used Mk 20's and Mk 25's successfully with D400 second stages in 35-38 degree water at 150 ft depths. However, I have seen Mk 20 and Mk 25 first stages used with the S600 second stage freeze on a frequent basis in the same conditions.

If you use low pressure tanks (2250-2640 psi), a good cold water second stage (D400, G250HP, X650, Balanced Adjustable) and good cold water technique the Mk 20 may work well for you at temps below 40-45 degrees. But...I switched to the Mk 17 because "may" just did not leave me feeling very inspired. And in fact prior to the release of the Mk 17, I reverted to using the SPEC system on my Mk 20's as it is much more relaible in cold water than the TIS system.

FWIW I have seen 42F referenced a few times as the point where you want to be considering a cold water rated system.