coldstroke
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Which one breathes better? Why?
SP D400 or SP Bal. Adj-better breather?
- Thread starter coldstroke
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Both are great regs and both have poppet designs that allow very low inhalation efforts. The D400 however is a better breathing reg in real world conditions.
Conventional regulator designs like the Balanced Adjustable suffer from a case geometry flaw where the ehxaust valve is substantially higher than the center of the dipahragm in some positions (such as when looking straight down. What this means is that the air inside the second stage will leak out the exhaust valve until the pressure inside the case is equal to the pressure at the exhaust valve rather than an inch or so deeper at the center of the diaphragm. This causes the diaphragm to move inward and if the lever is depressed far enough to initiate air flow before the pressure is equalized, a slight freeflow will develop between inhalations. In order to prevent a freeflow the inhalation effort has to be set high enough so that the pressure difference between exhaust valve and diaphragm does not initiate airflow. This effectively limits the usuable inhalation effort to about 1.0 Inches of water.
With the D400, the exhaust valve is mounted coaxially in the center of the diaphragm, so the difference can never be more than the radius of the exhaust valve - about 1/2". Plus the diaphragm is angled so that the worst case position does not occur in a position the diver normally finds himself in. In fact in a normal swimming position the difference in height is zero. The resut is that you cna get optimum poppet performance in the .5 to .7" of water range and actually use it in the water with no need for adjustment or concerns about lack of stability in some positions.
In addition, the D400 is a very smooth breathing regulator that delivers air directly into the mouthpiece and does not have the turbulence that usually occurs with a conventional regulator design where the air usually has to make a bank shoit out of an airbarrlel in the center of the second stage to a mouthpiece toward the upper edge of the second stage.
In 2003 Scubapro "replaced" the D400 with the X650. The X650 used a good performing poppet similar to the S600 and was easier to adjust than the D400, but while it had the angled diaphragm design it lacked the coaxial exhaust valve and with an exhaust valve in a conventional position, the case geometry issues are in fact aggravated compared to a conventional second stage design. The engineers really screwed it up and/or did not understand diving or the mphysics involved and SP really stepped on it's member by discontinuing the D400 in favor od the X650. Not surprisingly the X650 is being discontinued only 3 years after being introduced.
However if SP were to modify the X650 design to incorporate a coaxial exhaust valve/diaphragm it would be a real winner of a regulator that is both an exceptionally sweet breathing reg like the D400 with an S600 style air barrel that would be familiar to and easy for iregulator techs to adjust. The principle engineering challenge would be to adapt the long lever needed for a conventional air barrel aligned with the mouthpiece to work with a coaxial diaphragm/exhaust valve design.
Conventional regulator designs like the Balanced Adjustable suffer from a case geometry flaw where the ehxaust valve is substantially higher than the center of the dipahragm in some positions (such as when looking straight down. What this means is that the air inside the second stage will leak out the exhaust valve until the pressure inside the case is equal to the pressure at the exhaust valve rather than an inch or so deeper at the center of the diaphragm. This causes the diaphragm to move inward and if the lever is depressed far enough to initiate air flow before the pressure is equalized, a slight freeflow will develop between inhalations. In order to prevent a freeflow the inhalation effort has to be set high enough so that the pressure difference between exhaust valve and diaphragm does not initiate airflow. This effectively limits the usuable inhalation effort to about 1.0 Inches of water.
With the D400, the exhaust valve is mounted coaxially in the center of the diaphragm, so the difference can never be more than the radius of the exhaust valve - about 1/2". Plus the diaphragm is angled so that the worst case position does not occur in a position the diver normally finds himself in. In fact in a normal swimming position the difference in height is zero. The resut is that you cna get optimum poppet performance in the .5 to .7" of water range and actually use it in the water with no need for adjustment or concerns about lack of stability in some positions.
In addition, the D400 is a very smooth breathing regulator that delivers air directly into the mouthpiece and does not have the turbulence that usually occurs with a conventional regulator design where the air usually has to make a bank shoit out of an airbarrlel in the center of the second stage to a mouthpiece toward the upper edge of the second stage.
In 2003 Scubapro "replaced" the D400 with the X650. The X650 used a good performing poppet similar to the S600 and was easier to adjust than the D400, but while it had the angled diaphragm design it lacked the coaxial exhaust valve and with an exhaust valve in a conventional position, the case geometry issues are in fact aggravated compared to a conventional second stage design. The engineers really screwed it up and/or did not understand diving or the mphysics involved and SP really stepped on it's member by discontinuing the D400 in favor od the X650. Not surprisingly the X650 is being discontinued only 3 years after being introduced.
However if SP were to modify the X650 design to incorporate a coaxial exhaust valve/diaphragm it would be a real winner of a regulator that is both an exceptionally sweet breathing reg like the D400 with an S600 style air barrel that would be familiar to and easy for iregulator techs to adjust. The principle engineering challenge would be to adapt the long lever needed for a conventional air barrel aligned with the mouthpiece to work with a coaxial diaphragm/exhaust valve design.
mahjong
Contributor
As usual, DA said it all. I can only add my two cents from experience. I dive mainly two SP second stages--a metal B/A and the D400 (and with both, I use an MK10 first stage). The D400 definitely breathes a bit smoother and easier, and I have also found that I use up air a bit faster with the D400. I have found that my mouth dries out more with the D400, and the D400 does not have great bubble exhaust dispacement (I spear fish, so if I'm stationary, my vision is washed out with bubbles when I exhale). The B/A also breathes great, and my mouth stays moister and bubble displacement is better (wider exhaust tee). Sharks are around in the summer, and just in case any flash from the metal case of the B/A might draw a tiger or bull shark's attention toward me, I use the D400 until the fall, when I switch back to the B/A. Both are great regulators, in my opinion.
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