Deep dive and user adjustment knob

[dandecraene]

Has anyone had an issue while deep diving (95 feet) where their second stages began to free flow and they need to dial the user adjustment knob back (clockwise)? Per most manufacturers this adjustment may be needed in current or while inverted, but it seems to me a probable need at depth due to higher water density vs ambient pressure in the second stage. Thanks for reading.

 

[BoltSnap]

Nope, I turn it all the way out before descending and never touch it again while underwater any depth. Same thing for the venturi adjustment when second stage is in my mouth. My Atomic regulators have manual/diver cracking pressure adjustment and an automatic adjustment for venturi but my SP's have both manual/diver adjustable.

 

[JackOfDiamonds]

My reg doesn't have a venturi / adjustment knob, never needed it.

Viva la Abyss

 

[Angelo Farina]

Has anyone had an issue while deep diving (95 feet) where their second stages began to free flow and they need to dial the user adjustment knob back (clockwise)? Per most manufacturers this adjustment may be needed in current or while inverted, but it seems to me a probable need at depth due to higher water density vs ambient pressure in the second stage. Thanks for reading.

Which reg is this?
Is it tuned to the edge of freeflowing, or with same margin before the edge?
I have a number of of old Scubapro MK5 + 109 (al converted to 156). O couple of them are tuned "to the edge", and these easily go freeflowing with the knob completely uscrewed. Just half a turn and they stop freeflowing.
I did not find a specific association with depth (indeed, 95 feet is not "deep diving" in any sense", it is just a "normal depth" at which any regulator should work reliably).
Instead I have found a significant correlation between freeflowing and the inclination of the reg: when swimming horizontally with the diaphragm looking forward-down they free flow easily, if you look up they stop.
I did not grasp your explanation about water density at depth. Water density does not change significantly with depth. Air density, instead, changes a lot.
Air density is important for the Venturi effect, but has no effect on the "cracking" depression required for starting the flow.
For "freeflowing", do you mean that the reg starts releasing air by himself, or simply that, once "cracked open" with your depression, then the valve remain open due to Venturi?
In the first case, it appears to me a typical problem of a not-balanced second stage when the first stage over-reacts to ambient pressure variations (some regs makes it by design), hence the deeper you go, the higher will be IP above ambient pressure, so that it will win the spring keeping the second stage valve closed.
A balanced reg, as my modified 109s, do not suffer of IP variations.
The Venturi extra effect, instead, is due to excessive Venturi loading of the diaphragm. My regs do not have any Venturi vane, so again they do not suffer of this problem.
If your reg has a Venturi vane, probably it is improperly oriented, causing this excessive venturi effect at depth.

 

[BoltSnap]

My reg doesn't have a venturi / adjustment knob, never needed it.

Viva la Abyss

How do you know that you didn't need it if you don't have it?

I have sold and worked on the abyss MR22 for years through all of its variations and was actually the service center for them and having the once director of service and warranty for Mares work for me in our service department at my dive center, it was a piece of fish dung. I owned one for less than a year and got rid of it and never went back to it again! Once you try SP or Atomic regulators at all levels of diving, you never go back to the Abyss or anything else (and don't get me going about the Rubby Abyss fiasco). The best regulator Mares made as a solid entry to mid-level regulator that was rental tough was the MR12 Navy but that was long time ago and it is no longer available.

 

[kensuf]

What's the first stage? On some first stages (Apeks DS4/etc), the intermediate pressure goes up at depth. This shouldn't cause freeflows at 95', but I have seen that happen deeper than 250'.

 

[tbone1004]

Has anyone had an issue while deep diving (95 feet) where their second stages began to free flow and they need to dial the user adjustment knob back (clockwise)? Per most manufacturers this adjustment may be needed in current or while inverted, but it seems to me a probable need at depth due to higher water density vs ambient pressure in the second stage. Thanks for reading.

most all sealed diaphragm first stages will do this. That is part of what they call "overbalanced" which is actually "overcompensated". The relative IP increases as you go down. If your reg is tuned right at the edge for optimum performance, it will freeflow at depth. Perfectly normal, nothing to worry about. I say freeflow, but it's more like an ever so slight leak at 100ft, deeper will become more pronounced, but it's nowhere near what you think of when you hear the word "freeflow"

 

[BoltSnap]

There is -considerable- difference between "freeflow" and "air leak" in this context.

 

[JackOfDiamonds]

How do you know that you didn't need it if you don't have it?

I have sold and worked on the abyss MR22 for years through all of its variations and was actually the service center for them and having the once director of service and warranty for Mares work for me in our service department at my dive center, it was a piece of fish dung. I owned one for less than a year and got rid of it and never went back to it again! Once you try SP or Atomic regulators at all levels of diving, you never go back to the Abyss or anything else (and don't get me going about the Rubby Abyss fiasco). The best regulator Mares made as a solid entry to mid-level regulator that was rental tough was the MR12 Navy but that was long time ago and it is no longer available.

Because I never encountered issues with it as I did with other regs, breathing difficulty is very easy and consistent regardless of depth or pressure .

I haven't tried Atomic but I did do a couple of dives on the MK17 & Legend , they are awesome regs but my reg is functioning so well I have a hard time finding an excuse to upgrade.

 

[rsingler]

While the issue of first stage contribution to possible free flow has been addressed above, there is a second factor at depth that might be considered: increasing Venturi effects due to higher gas density. @Angelo Farina hinted at it above.
When the Scubapro G250 was first introduced, the VIVA vane was adjusted by the technician, and not the diver. It was set so as to self-terminate freeflow after 1-2 sec, by introducing some turbulence.

Assuming for argument's sake that increasing IP at depth due to overbalancing or effects of an environmental seal is not at work, then the next most likely possibility is not true freeflow, but "crossover" from barely negative cracking effort to positive freeflow with each breath, or "chipmunk cheeks."

Increasing the cracking effort by screwing in the adjustment knob will help, but at the cost of higher breathing effort. If this isn't spontaneous freeflow but rather crossover, then the solution is to slightly reverse the Dive/Pre-dive switch. That leaves cracking effort intact, but adds enough turbulence to reduce Venturi suction on the diaphragm, eliminating crossover.

Now, what the OP described is more probably related to IP rise in a hot-tuned second stage (since it's happening as shallow as 95'), but a complete discussion of the possibilities shouldn't omit crossover.