Tweaking SP MK25/S600 for cold water

[O'Malley]

I will be doing my drysuit certification in a few weeks and was advised by LDS to have the pressure tweaked down on the MK25/S600 and to "back off" the hose protection covers, exposing the hose connections to the first stage to avoid free flow; the water temperatures last weekend were reportedly 39 degrees F. Is this common practice? I have only dove this regulator, without occurance of free flow, in water temperatures 48 degrees F and above.

Thanks...

 

[DA Aquamaster]

At temps much below about 50 degrees the Mk 25, and in particular in combination with the S600 second stage, the Mk 25 can freeze up.

Backing the hose covers off the metal parts of the hoses increases the area available for heat transfer from the water to the first stage and will help prevent a freeze up. You also want to do the same thing with the trim boot covering the inlet fitting on the S600 as well.

Reducing the intermediate pressure on the MK 25 to around 120-125 psi will reduce the flow rate from about 300 SCFM to about 250 SCFM and will help slightly to reduce the possibility of a freeze up if the reg falls out of your mouth etc. It also reduces the amount of pressure drop in the second stage as air moves past the second stage poppet and drops to ambient pressure. Reducing the amount of this pressure drop will reduce the amount of cooling that occurs in the second stage and will reduce the potential for ice formation in the second stage.

 

[Uberlingcod]

I dive in water temps around 45F all year and have never had a problem. Scuba pro does make a kit which can be installed for cold water conditions I can not remember what it is called.

 

[mahjong]

Recently dove my MK25/Balanced Adjustable combo in 35 degree salt water. My MK25 was only slightly detuned, and same for my B/A--my technician also adjusted the internal lever so that it wasn't resting on the diaphragm. Also backed off the hose protectors.

Had no problem on the dive.