Cheap Octo Performance: Worse than you might think

[StSomewhere]

Its just as I have always suspected. WOB scores do matter.

Our British friends at the HSE have determined that the crappy octo you may have bought with your regulator performs worse than you probably thought when two divers are breathing from the same first stage, and may not meet their EN250 standard when both second stages are in use.

Links to the DiveNews.com article, and the original British HSE Research Report.

Basically, they recommend a completely independent gas supply and demand regulator as the best option, as opposed to the standard single first stage with two second stages. I read this to mean doubles, an H-valve, or stage/pony bottles.

Otherwise newer, high performance regs should be used. The higher performance (and higher priced) regulators did much better than the cheaper or older regulators, and most importantly the poorer breathing octos performed significantly worse than the primary as load or depth increased.

I, for one, am glad I went with basically the same backup reg as my primary.

 

[BIGSAGE136]

I still dont understand the draw of CHEAP life support. :06:

 

[MoonWrasse]

I still dont understand the draw of CHEAP life support. :06:

Cheap buddies?


Having only skimmed the report (I'll read the 41 pages later) one thing caught my eye: the importance of out of phase breathing when two people are breathing off of a single first stage. This hints at the importance of technique as much as equipment expenditure.

:diver: ctopus: :diver:

 

[mwn]

Haven't we all practiced sharing air which involves 2 people drawing from the same first stage? When I certified, I used rental equipment, and we never had any problems. We did it many times, and never a problem.

Not that I would skimp on a regulator.

 

[DA Aquamaster]

I have not read the report, but it the conclusions you state are pretty obvious.

If a diver is huffing hard enough on even a cheap octo to fully depress the demand lever, it will have a flow rate of about 30 SCFM. On a high performance second stage this figure will be between 50 and 70 SCFM.

So if an OOA diver steals your high performance primary and sucks on it for all he is worth you had better have a good first stage as he will be sucking 70 SCFM for the second or two it takes him to inhale and you and the cheap octo will be stuck with whatever remaining air your first stage can supply.

In a worst case scenario with a first stage that can only deliver 70-90 SCFM, common flow rates for unbalanced "flow by" piston first stages on a full tank, there may not be much capacity left to feed the octo you are now breathing off. Both of you may end up outbreathing the first stage and one or both of you may feel that you are not getting enough air. And the situation gets much worse at lower supply pressures where the flow rate is decreased. In extreme cases, one of you may even spit the reg out and bolt for the surface if panic ensues.

What is almost as bad is that even with a moderate performance second stage (with a flow rate in the 150 SCFM range) the large flow rate on the primary second stage may still drop the intermediate pressure substantially (up to perhaps 25-30 psi) so that your inexpensive unbalanced Octo will now have to function at an effective IP well below what it is designed and tuned to operate at. That will result in less downstream force acting to open the unbalanced second stage poppet and in turn will require a much greater inhalation effort to develop the force needed to open the poppet. And even once the poppet is open, the flow rate will be reduced due to the lower IP. So if you are also seriously in need of air, you may not get enough of it. This effect can be worse with diaphragm designs that often have a slower response rate and less flow rate than "flow through" balanced piston designs which results in a greater potential drop in IP when paired with high performance second stages.

Buying a high performance first stage has always been a good idea if you are doing any type of deep diving. And the smart money has always been on using an octo that is equal in performance to your primary because:

1) you will be the one using it, not your buddy, and
2) a higher performance balanced Octo, all other things being equal, will perform better at a reduced IP than a cheaper unbalanced Octo.

 

[moxie]

shallow water, so didn't have any problems. The same thing at 100' or so might overtax some older or lower end reg sets. WOB really counts at depth.

 

[StSomewhere]

DA Aqua, for someone who didn't read the report you have an amazing grasp of the issues and conclusions. You can work on my regs anytime.

After rereading the report last night, one thing still gets me. In the case where the two second stages have different performance characteristics, the performance of the poorer performing regulator (probably the octo) seems to decreases exponentially, not linearly. And yet, many LDS's sell most of their regulators in that exact configuration. Frightening. :11:

 

[PugetDiver]

I guess I may be missing something. In reading this test, I did not see a scenario where a high performance 2nd stage is paired with a low cost OCTO from the SAME manufacturer. I would like to see test results on this pairing as many if not most configurations are of the same manufacturer. If I missed something please let me know.

 

[StSomewhere]

Correct me if I'm wrong, but I don't think it matters PugetDiver. Low performance second stages perform like a low performance second stages, no matter who made it. Same deal for the first stages.

 

[PugetDiver]

Correct me if I'm wrong, but I don't think it matters PugetDiver. Low performance second stages perform like a low performance second stages, no matter who made it. Same deal for the first stages.

I was under the impression that it is best to stick with the same manufacturer when it comes to your regulators.

Are second stages so basic that they will work with any 1st stage? There is no tuning that needs to be done when different manufacturers of first, primary and secondary stages are mixed?

Bear with me as I am new to all this. I am just trying to figure out why they failed to include a high end regulator and low end (inexpensive, basic, non adjustable) octopus from the same manufacturer in their otherwise in depth testing.