Aqualung ABS octo intermediate pressure???

[Speardoggin]

My girlfriend just bought an Atomic Z2 and an aqualung ABS octo to go with it. Im just not sure that they are compatible. What is the intermediate pressure for the AL ABS octo?

 

[SDAnderson]

Atomic 1sts = 125 - 145 psi.
ABS = 135 - 145 psi.

 

[Capt.Gene]

Actually you tune the 2nd stage to the supply press it recieves from the 1st stage.

 

[Speardoggin]

Actually you tune the 2nd stage to the supply press it recieves from the 1st stage.

Please explain how that is different than intermediate pressure.

 

[Bubbletrubble]

Please explain how that is different than intermediate pressure.

I think Capt.Gene was explaining the following...
The 1st stage steps down the higher tank pressure to an intermediate pressure (IP; 135 - 150 psi usually).
IP is adjusted on the 1st stage.
When tuning a 1st stage + 2nd stage reg setup, the reg tech will first adjust the IP on the 1st stage to be within the manufacturer's recommended range.
Next, the reg tech will adjust the cracking pressure (pressure at which flow starts) of the 2nd stage to be within the manufacturer's recommended range.
AFAIK, for its 2nd stages, Aqualung specifies a cracking pressure of 0.8" - 1.4" of water for a primary 2nd stage and 1.2" - 1.8" of water for an octo.

In general, when one talks about the "tuning" of a 1st stage, it's understood that the speaker is referring to adjustment of the IP.
In general, when one talks about the "tuning" of a 2nd stage, it's understood that the speaker is referring to adjustment of the cracking pressure.
To confuse you a little bit, there are certain regs (e.g., Mares) where the manufacturer recommends fiddling with the IP on the 1st stage to fine-tune cracking pressure on the 2nd stage.

FWIW, most modern-day 2nd stages from one manufacturer can be mixed-and-matched with a modern-day 1st stage from another manufacturer. The only problem this might create is that, when it comes time to service the reg setup, the reg owner would have to find a reg tech who is authorized to work on both brands of regs. If the reg owner can't find such a reg tech, then he'll have to get his 1st stage serviced at one shop...and his 2nd stage(s) at another shop.

I used to have an ABS octo installed on an Aqualung Legend 1st stage. It worked OK, but the cracking pressure had to be set in the 1.5" - 1.8" range to decrease the possibility that the "overbalanced" 1st stage would cause it to free-flow at depth. Just one of the disadvantages of having a non-adjustable 2nd stage.

The bottom line is: a reg tech should be able to tune the ABS properly once it's installed on your girlfriend's Z2 1st stage.
If you are going to be your girlfriend's dive buddy, I'd make certain that her ABS octo cracking pressure is to your liking (so long as it doesn't cause any annoying free-flows while diving). After all, that's the 2nd stage you'll be breathing from in an out-of-air/low-on-air scenario.

Hope this helps...

 

[Zung]

I doubt anyone can tune that octo to a "likeable" state. I tried everything I know on mine, finally the best "tuning" I can find is to leave it at the bottomost layer of my closet.

Sorry.

 

[Bubbletrubble]

I doubt anyone can tune that octo to a "likeable" state. I tried everything I know on mine, finally the best "tuning" I can find is to leave it at the bottomost layer of my closet.

@Zung: I prefer my 2nd stage cracking pressures to be in the 1.0-1.25" range. I could never get the ABS cracking pressure in that range without causing a free-flow in the water.

I see that particular octo as a stop-gap measure until a better 2nd stage can be purchased.
Perhaps the OP will buy a balanced adjustable 2nd stage for his gf at some point in time.
The Atomic octos are nice, but pricey. Cheaper alternatives would be the Aqualung Titan LX, Legend octo, any Apeks octo, Zeagle octo, certain Scubapro 2nds, etc.

 

[aquaregia]

I doubt anyone can tune that octo to a "likeable" state. I tried everything I know on mine, finally the best "tuning" I can find is to leave it at the bottomost layer of my closet.

I had the same experience. I used it for a 40' for 0:40 once and my first breath on the surface tasted so sweet. I fully intend to demand to buddy breathe if anyone hands me that in an OOG situation.

Alternately, I have some old metal seconds. I'll carry one, and if handed an ABS, I'll unscrew it and put my own second on. Problem solved.

 

[Zung]

... Cheaper alternatives would be the Aqualung Titan LX, Legend octo any Apeks octo, Zeagle octo, certain Scubapro 2nds, etc.

Yep, that's what I do for the kids: they each get a SP R290/295 and that's OK. Anyway, they use more air than I do... for now.

 

[SDAnderson]

Actually you tune the 2nd stage to the supply press it recieves from the 1st stage.

Sure you do but what happens if the 1st stage output range and the 2nd stage inlet range don't overlap - that's the problem OP is trying to avoid. You and I may know that this isn't a problem with most regulators (but is with some) but he doesn't and he's asking a smart (if rookie) question. Suffice to say that OP's two units will perform together.

Cracking pressure is off-topic to the question but I will add this to the muddle: cracking pressure isn't all it's cracked up to be. How hard you have to draw to start the flow is less important than how much gas the unit supplies once you open the valve. Some other thoughts:

• There are a number of factors that go into determining optimum cracking pressure, probably most important is case dynamics followed by intended use, anticipated case orientation, environmental conditions, supply pressure and, finally, user preference.
• Most folks will be happier if their alternate 2nd cracking pressure is set higher than their primary 2nd. If you or your buddy need to breathe off the alternate, you'll be excited enough that you'll never notice that it opens a little harder. In the meantime, the reduction in dribbly (or worse) free-flows that results from the extra tension will be appreciated. The ABS specs call for 1.2 to 1.6 inches in most circumstance, about .2 higher than, for instance, a Titan 2nd used as a primary. If you're diving in cold water you'll probably want to go even higher than that, maybe even if you reduce the 1st stage IP.
• If you want any 2nd stage to have a 1.0 - 1.2 cracking pressure, you really need to spend the money on an adjustable cracking pressure and adjustable Venturi. They cost a little more to buy and fail a little sooner unless well maintained but are highly effective.