Scuba Tech:
Non of the ports on a mk17/16 ARE "HIGH FLOW" this 1st stage does not have any venturi assisted ports. What they mean is that the indicated potrts on the 1st stage are closer to the main valve and, do not have to travel down a bypass within the body to reach the port's. This is not a high performance 1st stage despite what you may have read, configure it any way you want, at 100ft you wouldnt know any differance!
Hmmm. My Mk 17's are currently on the boat but I thought there was one port per side that was a high flow port.
But I agree the difference if any is minimal as all of the ports are in the main internal chamber with good flow.
As for not being high performance, that's a relative statement. The Mk 10 was considered to be "high performance" and with the old flat seat it had a flow rate around 120 SCFM. Now they probably have around 140-150 SCFM with the newer concave seats. Which as it turns out is more than adequate for any rec or tech purpose. Back in the day, I never ran short of gas on a Mk 10 during deep air dives to around 150 ft.
It makes sense when you consider that you can't get a second stage that flows more than about 65-70 SCFM anyway. So once your first stage can support two full blown freeflowing high performance second stages and have some left over for dry suit infaltors, etc. there really is nothing left in terms of "need" for more flow rate.
The Mk 25 in contrast has a flow rate of 300 SCFM out the end port and about 240 SCFM out the side ports. So I suppose it is superior in that you could have four freeflowing high performance second stages attached to it if you prefer - but I don't see any reason or it.
In comparision to that, the Mk 17's flow rate of 177 SCFM is arguably less, but it is still well over the 150 SCFM mark where anything extra is just gravy. And by any standard other than the Mk 25's excessive 300 SCFM flow rate, the MK 17 is definitely a high performance regulator.
I have taken my Mk 17's to 150 feet on air with no issues at all, I have used them on very hard working commercial dives with no shortage of gas and if you go deeper, helium mixes flow through them even easier and more than compensated for the increased depth. So all in all the Mk 17 offers more than enough performance for what ever a diver might do with it.
In terms of subjective breathing performance, I use D400 second stages adjusted to inhalation efforts of about .6 to .8 of water. These are arguably the best breathing second stages ever produced and I can tell absolutley no difference in breathing quality between the Mk 25 and Mk 17 on the surface or at depth, so obviously the MK 17 is not experiencing any lag or IP drop issues even at depth.
Personally, I feel the flow rate on the Mk 25 is excessive and I'd gladly trade trade some of that excess flow rate for cold water reliability - which is basically what I did when I retired my Mk 20's and Mk 25's for Mk 17's.
