Scuba Pro MK20 with D-400 2nd. Is it Safe??

[dimitrik]

This is some great information. I am new to diving and recently picked up a MK15/D400 that I just got serviced. I had the opportunity to try it out in the pool and just loved it. It was much easier to use than the dive shops Aqualung that my Brother was using. The only problem was that it had a "light" freeflow that I couldn't get to stop, but it was free flowing from the exhaust instead of the mouthpiece. I gave it back to the tech and after a few minutes of tinkering he said he fixed it.

I really don't know anything about this stuff and I haven't really tried to many regs. I'm not even certified yet. I was just doing my 3rd discover scuba session trying to get my brother hooked so he could do the class with me.

All I can say is that compared to my previous sessions, the D400 was far easier to breath on than the other regulators I had previously tried. And the best part of all is that I picked up the MK15/D400 for only $50.

Once again thanks to everyone on this board for thier wealth of knowledge. I feel way ahead of the game going into my classroom and pool training because of it.

 

[DA Aquamaster]

DA

Is there a problem if the SP adjustable is tuned to FF in the full open position? I believe the Oceanic adjustable 2nd tuning spec call for setting the orifice with the adjustment knob at the 1/2 way position. I have set my BA up that way just to see how easy I could make it breath. Turned out to be something my "sensetive" lungs didn't care much about. But I'm thinking that managing slight FF with the adjustment knob should be part of "normal" operator procedures with a user adjustable (cracking pressure) 2nd rather than an indicator of service requirement.

SP says essentially the same thing and suggests the orifice be adjusted with the adjustment knob in a mid range position, but I have never seen any advantage to doing it this way.

Personally, my preference is to leave the knob all the way out and then adjust the orifice to tune the reg to just short of a free flow with the knob all the way out. In the water, the knob then ends up being adjusted a couple turns in to prevent a freeflow in most swimming postitions. But it still leaves you adequate room to lighten the cracking effort in swimming positions where you can and it leaves you more room to tighten the knob down in a heavy current or to accomodate an aging seat during the dive season.

Some knobs on the original Adjustables and early BA's seem to be threaded a bit funny and will pull back disproportionately far on the last 1/4 turn or so. On one of these, I'll tune them with the knob a 1/4 turn or so in to avoid that particular complication.

I agree with you that with an adjustable regulator, the diver can correct for any seating groove effects that occur in a new soft seat so they are a lot easier for the tech to set up as the consequences of getting it wrong are diver correctable rather than a need for service. Most divers if they measured things carefully would probably also find that they need to turn the knob in slightly farther over the course of the season as the seat wears.

 

[WarmWaterDiver]

Love my D400 - better than my S600. Don't think I'll buy a X650 based on all the info available. I'll keep my eyes open for another D400 'deal' . . .

 

[liberato]

I'm curious about something. The one D400 I have seen had no adjustment knob as was mentioned above (other than the dive/pre-dive switch). Were there different versions?

 

[ericpitar]

DA Aquamaster said:
One of the bigger mistakes is in adjusting the spring tension on the poppet where the tech does not turn the spring adjustment pad past the desired position and then back, which consequently "winds" the spring a bit, and pretty much guarentees the poppet will leak a dive or two later. The other common mistake is to take the slack out of the lever before completing the adjustment of the poppet.

My question--Are these mistakes avoidable if the tech follows the SP manual or is it a "grey area" that it's silent about?

 

[DA Aquamaster]

There is a D400 service guide but it is not available on the Scubapro dealer/tech website, so if a tech does not have access to an older paper copy, they may not have it. One of the major motivations of replacing the D400 with the X650 was that the X650 used the same basic popet design as other SP balanced regs - it is just a shorter version of the S600 poppet.

Apparently they felt it was easier to replace the D400 than it was to properly train techs. That said the D400 could be a bit prone to slight freeflow if tuned for maximum performance and that probably led to a higher than average number of returns to the shop for re-adjustment. That could easily be prevented by increasing the cracking effort to the 1.0 range, but the reg then loses some of its exceptional performance.

THe X650 as it turned out was only produced for a couple years and has been discontinued as it was still "different" to service and it ne er offerred any advantage over the S600. If Scubapro still had a very talented engineer combined with an interest to recreate a reg with D400 performance, it could be done by redesigning the X650 to utilize a coaxial diaphragm and exahaust valve like the D400.

The thing is the vertically mounted center balanced valve design of the D400 was much more ammenable to the coaxial exhaust and diaphragm than is a horizontally mounted air barrel with a conventional balanced poppet design, so designing the lever and the lever/diaphragm interface is a bit of a challenge.