I wonder about clearing the reg though. Since it has no purge, if you have no air left in your lungs, what is the procedure?
I have also read about the physics of double hose regs but I am unclear about easier / harder flow due to position in water.
Diskskip,
I'm no pro at it, but I do enjoy my Cyclone/HPR DAAM.... in response to clearing, there are 2 methods I use that don't require full lungs.
First is to rotate the mouthpiece to face down and hold it above the level of the cans briefly (this will make it freeflow and the downward facing mouthpiece will trap the air bubble) then rotate it into my mouth. That leaves minimal water in the mouthpiece, allowing that first breath. My other approach is to just put the flooded mouthpiece in my mouth, and use my tongue to puff my cheeks in and out. With each "puff" out, a little water goes out the exhaust non return, and on the inward "puff" a little air comes in. The mouthpiece clears pretty quick that way.
After either method, exhale while rolling approx 90 degrees left (making the exhaust on the can the lowest point of the loop) to clear the water out of the exhaust hose.
As for the DH position in the water effecting breathing... it does, but good can positioning will minimize the effects. To oversimplify it, second stage regulator cracking pressure is measured in inches of water... based on center of diaphragm vs mouthpiece. In a normal diving position (flat or near flat trim) and the cans positioned below the base of your neck, it will crack (initiate a breath) at a very similar effort to a single hose reg. But if you roll on your back and surface swim with the mouthpiece in you mouth... now the diaphragm (in the cans) is underwater by 6 to 12 inches while the mouthpiece is in your mouth.... so it will chipmunk your cheeks out with 6 to 12 inches of water pressure (feels almost like it is trying to force you to inhale) and exhaling is against that same pressure (the loop's exhaust is right by the diaphragm). Roll head down and get the cans above lung height, and the exhale is super easy... but cracking pressure goes up. The better you get the can positioning (closest as possible to the top of your lungs and tight to your back) the less orientation in the water effects breathing resistance.
Hope that helped some.
Respectfully,
James
edit to add: Cheeks getting chipmunked out is separate from actual cracking effort changes... the work of inhale/exhale is done by the lungs (which should be close to the cans) while the cheeks feel the pressure differential of their vertical distance from the can. You can have the cans on the same level in the water as your lungs and your head up and get chipmunked cheeks even though the actual breating resistance is normal.