octopus vs. regulator

[ifukuda]

MikeFerrara,

The guy at the shop actually did dunk my octo in a bucket of water to test. But, when I asked him if he had fixed my freeflow problem, he told me he wasn't sure.


gulfdiver,

I actually never said that my free flow was "bad." But, isn't any unwanted air loss bad?

I don't think the freeflow started at the surface (at least, I didn't hear it). I didn't notice the freeflow until I was 20ft under. Also, the air wasn't gushing out like it would when I hold down the purge button. It was more similar to a stream of bubbles that a diver would exhale. At first, I thought the bubbles from the primary (in my mouth) was getting into my face. But then, I realized that there was too much air in my face and looked down to find my octo was graciously oxyginating the waters of Laguna Beach at the expense of my bottom time.

 

[Douglas]

After opting for the Air II - to simplify the kit, but also because it looked cool, and diving about 10 dives with it, I'm changing it for a regular octopus.

It's position is great - always in the same place.

It's not at all possible to offer it to a buddy though. You have to offer your regulator instead, then take the Air II for yourself - not too cool.

It's true also, that you can't turn you head much with it.

It's rate of flow is much greater than the regulators I'm used to and it can be quite unnerving to have so much air pumping through.

In France - if you are responsible for other divers (Divemaster and up), you are obliged by law to have two complete first stage systems (regulator and octopus) so for me an extra hose is now unavoidable.

Doug

 

[ifukuda]

Is it possible to adjust the actual tension of the spring inside a second stage?

I have an octo with a freeflow problem. If the mouthpiece points up, even at a depth of 30ft (10m), the octo freeflows. A guy at the LDS made an adjustment to the octo (he gave the diaphram some slack before touching the arm), but this did nothing to resolve the freeflow. Unfortunately, I did not find out my freeflow problem was not fixed, until I jumped off a dive boat and submerged to a depth of 10m.

Since I had nothing to do (unable to dive on a 10 hr. dive boat trip), I opened up both the octo and primary second stages to see if I can find any differences. I noticed that the tension on the arm of the octo was a lot softer than on my primary. Barely touching the arm on the octo would make it release air.

There were no techs on duty when I took my reg to the shop to get looked at. When I described my symptoms to the only guy in the shop, he kept insisting that there was nothing wrong with my octo. He even told me that octo's are (and should be) preset to be a lot more sensitive than the primary second stage ... after a day long ride on a boat, I was too tired to argue with an obvious idiot.

I ended up buying a new octo because I was not about to sit out another boat dive beacause of a $80 piece of gear. But, I am curious to know if there is anything that can be done to my old octo to prevent (at least minimize) freeflows?

 

[Stone]

Originally posted by ifukuda
Is it possible to adjust the actual tension of the spring inside a second stage?

ifukuda,

The answer is "it depends on the type of regulator".

Spring tension on some 2nd stages (barrel poppet models in particular) can be easily adjusted with just a screwdriver.

Other regulators require special tools and the know-how. For example, you can ruin a low pressure seat while making an orifice adjustment if you don't depress the lever.

One way to check if the cracking pressure is set too low is to connect your reg to a tank and to slowly lower the octo into a sink of water with the mouthpiece pointing up. Octos are usually "de-tuned" so that the reg won't start flowing until the diaphragm is 1 to 1.5 inches under water. If your octo starts to flow at less than an inch, it is too sensitive (for an octo).

If you have a venturi adjustment, it should be set to "min"

Did you try breathing off the octo to see if it would stop freeflowing?

 

[ifukuda]

Thanks for the response Stone,

Did you try breathing off the octo to see if it would stop freeflowing?

Yes, I've tried breathing off the octo... it breathes (too) easily.
No, this did not stop the octo from free flowing once I pulled it out of my mouth and pointed the mouthpiece upward.

I don't think there was a screw adjustment on the octo. There was an allen wrench adjustment, but this one only seemed to adjust the play on the lever instead of the spring tension. Oh well, too bad.

FYI: The octo was a Mares Axis. Replaced it with a LPO, which breathes like s**t but won't free flow.

 

[Stone]

Originally posted by ifukuda
FYI: The octo was a Mares Axis. Replaced it with a LPO, which breathes like s**t but won't free flow.

The info I read on the internet says the Mares Axis is a good performer, and if properly adjusted, should not be prone to free-flow. In general, your 2nd stage should be tuned to match the Intermediate Pressure supplied by your 1st stage. Both your LPO and Mares might work fine with minor adjustments.

 

[TexasMike]

This past weekend, I had my first foray into being taught the basics of diving a technical rig (aka doubles, 7-ft. hose, and bungeed backup).

As part of the class, we practiced the out of air drills at several depths, including the bottom which was 83 ffw.

My contribution to this thread is that I appreciated having a high quality regulator as my backup. While I realize that a technical rig puts the back up reg on it's own first stage, it was nice being able to exert the same minimal effort to breath when sharing air.

Another thought is that it might be you who is using the "octo" if your out of air buddy starts over stressing and goes for the one in your mouth. So if this was the case, would you want to be breathing the low end, hard breathing reg while you solve the problem and you're stress level is rising?

-- TM (who all the time finds it fascinating how much thought must go into proper gear selection for our sport)

 

[oxyhacker]

There are two adjustments (if we can ignore venturi adjustments for a moment) that effect how easily a reg 2nd breathes, the lever height and the demand valve/poppet spring pressure, aka cracking pressure. Some 2nds allow you to adjust both, and are referred to as "two adjustment" 2nds, others just one, and are referred to as "single adjustment" 2nds. When a 2nd has only one adjustment it will almost always be the lever height. Usual practice on an octopus is to set the poppet spring pressure a little higher on an octopus, to make it less likely to freeflow, which can be done on a two adjustment 2nd just by increasing the spring pressure a bit. However, on a single adjustment 2nd the only way to increase the cracking pressure is to replace the poppet spring with a stiffer spring (or maybe, shim it). Some seconds sold specifcially as octopuses have a stronger spring installed which will make them breathe harder than is desirable when used as primaries, and inversely, the non-octopus version of the same reg may have a softer spring, which will make it breeathe easier but be less suitable for use in an octopus. Only a look in the manufacturers parts sheet can tell if this is the case.

Compounding the problem, on many single adjustment regs the lever height is adjusted exactly the same way as the spring pressure is on most two adjustment 2nds - by screwing in or out a little orifice located inside the fitting where the hose screws on. It is not unknown for a reg tech to be confused about the function of the two adjustments, or even not aware of the difference. If one such tech tries to adjust a single adjustment oct with a stiff spring to make it breathe easier, he'll usually end up cranking the lever up so high that's its fouling the diaphragm, which will make the reg unstable and erratic, and prone to freeflows in the water.

Originally posted by ifukuda
Is it possible to adjust the actual tension of the spring inside a second stage?
least minimize) freeflows?

 

[ifukuda]

Thanks for the insight oxyhacker.

The Mares Axis octo does not seem to have an adjustment for valve spring tension. You're explanation seems to be right on the money regarding the behavior of my old octo.

Is it expensive to replace the poppet spring? If it's not, I have a friend, who is shopping for a reg (and on a tight budget), that would like to take the Axis off my hands.

 

[Bob3]

Big difference, an octo comes off the same first stage as your primary reg.
A backup has its own seperate 1st stage.