I have a MK25 and a few different SP 2nd stages ("newer" D400, "older" D400, 1st Gen S600, and an A700)...I was wondering if using all 4 LP ports and breathing each Reg (in a pool) is a valid test to determine which 2nd performs best or if there would be any difference in pressures between ports that could affect second stage performance? Seems to me IP should remain constant with airflow only coming from 1 port at a time...but I thought I would ask. Thanks in advance.
Breathability Test
- Thread starter J_Rod
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a pool may not be the best place to test them.
i would think much deeper would be better.
a poor preforming reg will breath harder at depth.
use your regular two reg setup and test one against the other
you could test them over several dives, always keeping the best reg as your primary
do all testing at the same depth, same conditions
i would think much deeper would be better.
a poor preforming reg will breath harder at depth.
use your regular two reg setup and test one against the other
you could test them over several dives, always keeping the best reg as your primary
do all testing at the same depth, same conditions
As long as you are not using the 5th bottom port, all four ports will deliver air in the same manner. The difference with the bottom port is that the gas flowing through it does not have to make a 90 degree turn before reaching it's destination. The IP before the start of a breath will be the same regardless of which port is being used, however once you have been breathing for more than a split second the IP will drop and the first stage will begin to deliver gas and restore balance. As the air rushes down towards the second stage it will get slowed down a little every time it hits a bend, which means that it will take just a tiny bit longer to reach equilibrium at the second stage. In the case of the MK25, there is a 90 degree turn that the air will make to then start flowing down the four LP ports on the turret. The exception to that is the 5th port on the bottom that gets a straight run down the barrel of the piston and into your hose. This is designated as the high flow port.
Now, let me be clear about this. A diver will not be able to tell a difference in performance from one port to the next. These differences are noticeable in a lab on very accurate gauges, but not so much to a diver in the water. For the purposes of your test however, you can rest easy knowing that the playing field was absolutely level if you use the 4 side ports.
Now, let me be clear about this. A diver will not be able to tell a difference in performance from one port to the next. These differences are noticeable in a lab on very accurate gauges, but not so much to a diver in the water. For the purposes of your test however, you can rest easy knowing that the playing field was absolutely level if you use the 4 side ports.
Thanks for the responses...I was surprised with the results. Older D400 and S600 were VERY close with the edge going to 400 because it seems to deliver air more to my liking. My newer 400 was right there, too. The BIG disappointment is the A700....I thought it was fantastic until I had the breath by breath comparison. Maybe it needs to be serviced??
SCUBAPRO Harry
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J_Rod,
The information above describing the 4 LP ports and the in-line LP port of the MK25 is correct however true breathability testing of your second stages should consist of a couple things: 1) be sure they are tuned/serviced to their upmost performance 2) depth will affect many regulators perceived performance so the pool doesn't do the testing justice.
The information above describing the 4 LP ports and the in-line LP port of the MK25 is correct however true breathability testing of your second stages should consist of a couple things: 1) be sure they are tuned/serviced to their upmost performance 2) depth will affect many regulators perceived performance so the pool doesn't do the testing justice.
flots am
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Your MK25 has a flow rate that is actually greater than the tank valve (the reg capacity is limited by your tank valve flow rate). It's not possible for one or two humans to even begin to tax it's capabilities, so the number of ports you use or which one you select shouldn't be an issue.
There is some theoretical possible improvement by using the end port for your primary, but I've tried it and really couldn't tell any difference on even my deepest dive. Admittedly, there are lots of divers that go deeper than I do (mostly recreational depths, sometimes a little deeper), however I don't think it's worth giving a lot of thought to, and would prefer to use the port that gives the best hose routing.
As for your second stage, "which one breathes better" is almost certainly determined by "which one was serviced and adjusted by a really good tech".
I have several identical second stages that breathe a little differently depending on who serviced them.
flots.
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