Aqualung ABS octo intermediate pressure???

[Bubbletrubble]

• 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.

@reefraff: I have to disagree with you on this point. One does not need "adjustable cracking pressure" (I'm assuming you mean a user-adjustable breathing inhalation knob) in order to have a 2nd stage that is set for a cracking pressure of 1.0"-1.2". The Aqualung Legend and Titan LX do not have a breathing inhalation adjustment knob. My preferred cracking pressure setting for the Legend 2nd stage is 1.0". If I owned a Titan LX, I'd set it the exact same way. FWIW, my Legend octo is set at 1.0"-1.1".

Quite frankly, I think any good-quality 2nd stage (even without inhalation adjustment knob) should be able to be tuned in the 1.0"-1.2" cracking pressure range.

FYI, the Venturi adjustment shouldn't affect cracking pressure at all, so I'm not sure why you specified that as one of the two 2nd stage features required for someone desiring a cracking pressure in the 1.0"-1.2" range.

 

[SDAnderson]

@reefraff: I have to disagree with you on this point. One does not need "adjustable cracking pressure" (I'm assuming you mean a user-adjustable breathing inhalation knob) in order to have a 2nd stage that is set for a cracking pressure of 1.0"-1.2". The Aqualung Legend and Titan LX do not have a breathing inhalation adjustment knob. My preferred cracking pressure setting for the Legend 2nd stage is 1.0". If I owned a Titan LX, I'd set it the exact same way. FWIW, my Legend octo is set at 1.0"-1.1".

Quite frankly, I think any good-quality 2nd stage (even without inhalation adjustment knob) should be able to be tuned in the 1.0"-1.2" cracking pressure range.

FYI, the Venturi adjustment shouldn't affect cracking pressure at all, so I'm not sure why you specified that as one of the two 2nd stage features required for someone desiring a cracking pressure in the 1.0"-1.2" range.

Case dynamics play an integral role in how pressure differentials impact regulator performance. The distance between the center of the primary diaphragm and the highest point on the exhaust diaphragm needs to be subtracted from the "dry" cracking pressure to give you a "wet" cracking pressure. Depending upon the model and the orientation of the 2nd stage, the gap between the diaphragms can easily exceed an inch, in some that distance can come close to 1.5 inches. If you've set your cracking pressure to 1.0" when dry and you have a gap of 1.0" when the 2nd stage is held face down in the water, a bird flying overhead is going to cause the valve to open. If the gap is 1.2" the bird can take a break - the valve is going to open without any further assistance. If you've ever witnessed an alternate start to free-flow as the diver walks into the water, you've seen this how this works.

Once the valve opens and the gas begins to flow, the Venturi effect actually reduces the pressure inside the case in many modern regulators and makes it even harder for the valve to close. This may be counter-intuitive but it's still true. The reason for an adjustable Venturi lever is to allow the user to disrupt the otherwise laminar airflow inside the 2nd stage case, creating more back-pressure to help offset the sucking effect of a free-flow.

 

[Speardoggin]

Thanks for all the replies! We took the setup for a dive and it worked great (no free flows thus far). time will tell. She liked the Z2 a lot as well. For my personal setup, I use an A700/MK25 set at 1.0 cracking with 7 foot hose and Legend second stage on a necklace set at 1.2.