Scuba Pro MK V w/ 109 “Cold” Free Flow

[Erik22]

Hey guys. Experienced reg service tech here.
Let’s take a look at this situation and try to find an answer?

This is something that puzzles me. Recently I took my Scuba Pro MK V with balanced adjustable 109 conversion diving. The air temperature was 2 degrees celcius. The water was 3.8 degrees celcius. My tank was a PST LP 120 filled with 2100 psi air. The tank and regs were in the back of my wrangler, not a lot of heat back there (wranglers aren’t known for HVAC capabilities). So they were already “cold” before the dive setup.

As I attached the reg to the tank and began my pre dive checks, the second stage had a small leak.

This regulator has a cracking pressure of 1.1” H2O, and an IP of 123. All new o rings and service kit straight from Scuba Pro. Greased with MolyKote 111. 1 shim on the inside and mostly filled with silicone in SPEC chamber.

I knew it wasn’t enough of an issue to “abort” the dive and proceeded to dive for 30 mins at 35 feet, before my feet got numb.

I understand that this regulator isn’t exactly rated for cold weather or cold water, with “cold” being defined as below 40 degrees F.

Is it possible that thermal contraction caused a difference in seating capabilities?

It does not free flow at room temp 20C/68F. Leading me to believe it is the cold temperature that caused a failure.

I may end up moving the regs to a Conshelf, or just dedicate the MK V setup as warm water regs.

Erik

 

[happy-diver]

What a magnificent set of circumstances you have described, I would suggest definitely

 

[axxel57]

Sounds a bit strange.

A 2nd that starts to free flow by just connecting it at 2 degree celsius, but not at 20 degrees?

Did it free flow also while diving?

You were not able to check the IP at the time you were checking the equipment, right?

I have problems to imagine that a 109 starts free flowing just because of a 18 degree difference of temperature.

Thermal contraction? Of what? The LP seat?

If it would be a very old one, there might be a slight possibility that, if the 2nd had been adjusted very ‚hot‘, the seat might be a bit ‚too hard‘ to seal the valve perfectly, but I guess that was not the case here.

Can’t say from here what could have caused the small leak from just opening the tank valve for a pre dive check, but I’m sure it’s not the design of the MK5 and definitely not the design of the 109 (upgraded to BA).

I’d check the IP and the components, especially the LP seat for hard/softness and would not worry too much, with a slight turn oft he adjustment knob you should be able to solve the problem until you found the real culprit for this strange behavior.

I think a Conshelf could be only a help if the problem comes from the 1st stage, what I doubt, the Conshelf 2nds have no real advantage against the SP109, if there ist he slightest free flow there is no adjustment knob to eliminate it.

No problem at all with Conshelfs, they might have advantages in cold water diving because of their 1st stage diaphragm design, but for the problem described by you I don’t see any benefit switching to the Conshelfs.

 

[Nemrod]

What you are describing is not free flow but a small second stage leakage due to needing a tune up or adjustment of the orifice. Might have been set purposely hot to leak with the knob full out. Every G250, G260 and 109/156 I have, about a dozen I guess, all leak with the knobs fully out or at least want to.

As a seat and orifice take a set out of service, it is common for the regulator to leak. Most techs set the second stage regulators a little on the high side of cracking effort spec to account for the break-in to prevent that small leakage and a return by their customers. But some of us set the regulators hot, a slight leakage or nearly so, on our personal regulators purposely.

A first stage piston regulator will have a slight IP increase when the knife edge and HP seat come to agreement (after service), probably not enough to cause a leakage. But if the second stage was set right to the edge, maybe.

If your going to be using those 109s in cold water, you should probably increase the cracking effort after break-in to the higher end of specification and run the Mark 10s at the lower end of IP spec.

 

[Ghost95]

Is it possible that the seat material hardened in the cold and didn't allow a good seal?

 

[happy-diver]

Definitely!

 

[rsingler]

@Ghost95 hit the nail on the head.
Lots of seat elasticity and conformance to microscopic irregularities in the knife edge.

And @Nemrod had the right fix. Run a higher cracking effort. Your IP is already good.