cracking pressure

[HeatCker]

i had a cold water free flow earlier this year, start of the dive season, early june, wreck dive, lake ontario, 43 F, 71'
most of my diving is in shallow local lakes and rivers (less than 60' deep) and above 60 F.
Fall is setting in and local water temps are dropping.
between now and the end of dive season temps will be dropping from 60 to 40's F.
my dive shop just adjusted my cracking pressure to help with the free flow issue.
can anyone tell me what is involved in adjusting the cracking pressure.
i assume adjustments would have to be made both in the primary and 1st stage.
does adjusting the cracking pressure cause additional wear on the components.
my regs .. scubapro, MK17, S555
just curious .. thanks

 

[willcats]

Don't worry, your reg is fine. The cracking pressure is adjusted by moving the orifice in your S555 slightly, no adjustment is needed on the first stage and it does not cause additional wear on components.

Another cause of free flow would be high Intermediate Pressure in the First Stage, but the dive shop should have checked it when thy adjusted your cracking pressure. No need to worry there.

W

 

[Hickdive]

Cracking pressure is just how hard you have to inhale before the second stage valve "cracks" open and allows gas to flow.

Adjusting that pressure upwards will mean you have to inhale a little bit harder before you start to get air but it will only reduce the risk of freeflows initiated by pressure acting on the diaphragm and then sustained by the venturi. It will not reduce the risk of freeflows caused by low temperatures causing ice to form on working parts and freezing them open.

 

[HeatCker]

thanks for the input guys

 

[halocline]

The MK17 is reputed to be one of the most freeze resistant 1st stages available. I can't imagine that it froze on you in 43F water, there must have been something else going on.

 

[underH2Oman]

There are several factors that can increase the risk of freezing in a second stage.I believe you would benefit more by lowering the IP and adjusting the cracking pressure to 1.2-1.3 inches so that the regulator still breaths well.

Here is a great read regarding regulator freezing. http://www.divelab.com/assets/pdf/technical/ScubaRegulatorFreezing-ChillingFacts-4-9-14.pdf