Luis,
That conclusion comes from the graphs themselves. The same second stage was used on both tests. The graphs are dramatically different.
http://archive.rubicon-foundation.o...456789/4087/NEDU_1970_05letter.pdf?sequence=1
If you look at the graphs, you can see that at 200 feet sea water the Mk 1/Adjustable second stage was pulling just over 5 cm of inhalation resistance at 40 liters/minute RMV (2 liters per breath, 20 breaths per minute; adjustable valve open). The graph for the Mk 5, with the old-style ports (2 on each side) was pulling right at 10 cm water resistance to 200 feet, under identical RMV of 40 liters per minute.
I have seen other EDU tests which do use work of breathing in their evaluation, but that was after the Mk 1 was discontinued.
Evaluation of Commercially Available Open Circuit Scuba Regulators.
There is another evaluation I have somewhere, which does show a difference with the Mk 5, A.I.R. I combination depending upon which port was used. I'm trying to find that report now, but have not done so.
In the interest of fairness, I put together a fast test of my hypothesis, using my Mk 5/A.I.R. I combination. Here is that test:
Hypothesis
The end port on the Scubapro Mk 5 gives better flow rates than the side ports.
Test
Equipment: Twin 53 cubic foot cylinders and the Scubapro Mk 5/A.I.R. I regulator second stage.
Protocol
Each position will be tested for a 1 minute flow, using the purge button depressed to full extent. PSIG before and after 1 minute will be recorded. (I stopped the first test at 30 seconds because I was concerned about the flow emptying the cylinders.) Because of the hypothesis, the end port will be tested second. Readings will be recorded from my Cobra dive computer of psig before and after the test.
Discussion prior tot he test
The end position is postulated to provide an advantage because of straight-through flow. This has been challenged, and so this test will be conducted to determine whether there is a surface advantage. Testing the end position of the regulator will be done second because it would use a lower tank pressure. That should have no effect because the first stage is balanced. However, iic there is an advantage, it would occur for the first position tested (because of higher tank pressure). A Seiko Solar dive watch with a sweep second hand is used to time the test.
Results
A = side port; B = end port
Test 1......................Initial psig............Final psig...............Total psig lost (30 seconds)
A...............................1080..................960.........................120
B................................960...................840.........................120
Test 2 (one minute)
A................................840...................612.........................228
B................................612...................392.........................220
Test 3 (30 seconds)
B................................394...................285.........................109
A................................285...................177.........................108
Conclusion
There is no significant difference between the two positions at surface pressures. This is not surprising, as the study by the EDU only showed significant differences below about 100 feet of sea water.
Obviously, this is a rather primitive study, but it is the best I can do at the moment. It also does seem that the amount of pressure does influence the air flow, which gives an advantage to the first position (higher pressure) to be tested. The EDU used a constant pressure system in their tests of regulators, so that variable was not present in the EDU tests.
____________________________
So Luis, this confirms your position for surface use. I'll look to see if I can find anything else, but the story I heard about Scubapro changing its ports to include a top port stemmed from that study I cited above. I'll put some photos of my test up later.
Luis, I would like to see posted some of the test results you talked about. I like data, and don't just take word-of-mouth, which is why I used the EDU tests.
SeaRat
I do have a complete MK 5 with a heavy yoke. It has a 5 port turret, but only one 3/8'' hp port. It has recently been rebuilt. I can throw in a gauge and hose.
