1st stage free flow question

[Littorally Diving]

I'm 2 of 4 dives through my SDI OW certification, for background. Barely even a tadpole. Doing shore dives off Long Island and having a great time despite the three foot visibility.

I understand a bit about how second stages can free flow - water pressure hitting a down-facing purge button on entry, or by moisture in exhalations freezing up in very cold water. I know I can stop the former with a bit of back pressure; I know that the latter is not fixable underwater.

Can first stages free flow too? Is there any difference in how the problem manifests itself - in other words, am I just going to see a continuous stream of air coming out of my second stage that doesn't stop when I create back pressure, much like if the second stage had frozen? Would it come out of both of my second stages and drain the tank twice as quickly?

 

[runsongas]

first stage can suffer a failure in which the IP rises uncontrollably which will then cause a freeflow on the second stages. for most where the octo is tuned to higher cracking, the primary will freeflow first which then relieves the pressure such that the octo wont freeflow also, but if they are tuned very closely it is possible to have both flowing.

a valve shutdown could possibly resolve the issue on the first stage, but most likely would have to resort to redundancy, valve feathering, first stage swap if possible, and as a last resort bare valve breathing.

a frozen 2nd stage can be solved sometimes via a valve shutdown then switching to redundancy while waiting for the ice to clear up.

 

[rhwestfall]

as a new open water diver, it is about the buddy system when managing these things, and following your training that should be part of what you have learned....

 

[Littorally Diving]

Of course. My question is about the failure itself, not so much about what to do about it. First para. of runsongas' response covered it nicely.

 

[rhwestfall]

You need to understand the mechanisms. There are free flows (IP related in the first stage that leads to second stage issues, or maintenance related), but there are also freeze flows where icing in the second stage inhibits the full closure of the second stage mechanism... much of what you mentioned above.

 

[Jonny Wishbone]

And to add to what runsongas replied, if a 1st stage reg has IP creep, slow or fast, it usually means the high pressure seat is not happy the way it is mating with the cone that creates the seal. this could be from several reasons. the seat could be old and hardened enough that it does not seal right anymore. it could be a nick or little dent in the edge of the cone from debris that just happened to get smashed into the face of the seat when it closed. I remember back in the day when you used to run to blockbuster to rent a movie on VHS. it was raining one day and i got out of the car fast and slammed the door real quick just as the VHS tape slid off the seat and got crushed in the door when it slammed. so sorta like that. A properly maintained reg rarely has an IP creep issue. If the seat was not replaced on reassembly and the old seat was used, sometimes it won't seal right and will have IP creep. In rec diving it usually means you are going to abort the dive and keep your cool. you still can make it up fine. if you are low on gas you should think about learning how to feather the valve if no back up or pony tank is with you or your buddy.

 

[Littorally Diving]

"IP creep" is a gradual increasing of intermediate pressure in the hose between the 1st and 2nd stages? (As in what you'd expect if there was a poor seal somewhere in the valve between the high pressure gas in the cylinder and the IP chamber in the first stage?)

 

[divezonescuba]

This actually happened to me just prior to a 200 foot dive to the windjammer in Bonaire.

I had used the regulator all week and had also pressurized it prior to leaving the dive shop. On site, I repressurized it again. This time, it had a massive free flow. No amount of turning on and off the valve corrected the situation. Likewise, adjusting the intermediate pressure did no good. The gas was coming thru the second stage at essentially 3000 psi. I returned to my hotel room and replaced the first stage with a spare.

I performed an autopsy on return from the trip. Inexplicably, an oring had somehow gotten loose from somewhere or previously existed and was preventing the hp orifice from sealing against the hp seat. The regulator was new and had not been previously serviced. So, the whole thing was a mystery.

I am just glad it did not occur on the dive.

 

[Fibonacci]

I performed an autopsy on return from the trip. Inexplicably, an oring had somehow gotten loose from somewhere or previously existed and was preventing the hp orifice from sealing against the hp seat. The regulator was new and had not been previously serviced. So, the whole thing was a mystery.
I am just glad it did not occur on the dive.

I had a similar issue when servicing an Aqualung SEA Cousteau... the seal kit supposedly had OEM equivalent o-ring sizes but the one for the HP crown orifice was slightly too small, not enough preload and allowed the HP crown orifice body to shift into a slightly non-concentric position with its bore in the first stage body. This also affects its relation to the HP seat.
HP gas was then able to bypass the HP crown orifice o-ring and blew out the reg body end plug o-ring (which usually only handles IP level air) loudly venting full tank pressure. Irregular drifting IP was a hint, trouble was it held OK for two or three pressurisations then blew immediately. Glad that didn't happen underwater!
I had to measure all the components (incl the bore) and reverse engineer the o-ring size specifications, then checked against another reg with known OEM Aqualung o-rings.
Sure enough the non-OEM replacement o-rings were different enough to matter... Aqualung sometimes uses ISO Metric or French R series o-ring specifications.
For peace of mind, I just wish Aqualung (and most other SCUBA manufacturers!) would change their policy regarding selling their branded service kits to the general public!
And ALL divers should have a simple IP gauge that snaps into their BC hose and regularly use it as a health check of their equipment...

 

[Fibonacci]

a valve shutdown could possibly resolve the issue on the first stage, but most likely would have to resort to redundancy, valve feathering, first stage swap if possible, and as a last resort bare valve breathing.
.

I was (unofficially!) taught how to do that during my SSI Deep Diving course by the instructor who was an ex-RAN submariner... and thought it might be useful for us to know to build confidence. It did.
Incredibly, it works quite well and would indeed be a life-saver in a total UW catastrophe... but I can't see it being included in any OW course