D400 - Raising the w

[Scubadude_LA]

As usual, just got my MK15/D400 back from the wingnuts at my LDS after the proverbial PFLP annual servicing. 3rd dive dive into it while enjoying a nice dive on the Oriskany the D400 starts to deliver a moderate amount of air with no demand all the way to the surface. Shut it down, swaped tanks and it went away until about 1/3 the way through the next dive then did it again. IP good and locking up nicely, put one of my DR seconds on the MK15 and all was well next couple of dives until the din retainer came loose on the MK15. After two more weeks at the LDS I'm told it was fine and didn't have an issue (even though I told them the problem would not exhibit on the surface) and the real technician won't be back in the shop until late july.
This is the only reg set I have left that is under the lifetime warranty, but at this point and after a lot of bad luck with the LDS I'm done with them for good. Next nearest SP dealer is 1.5 hrs away and I don't really want to mail this thing out if I can help it.
I love this reg (been diving it for about 20yrs) but I'm at a point where I need to be totally self sufficient with my regs, I've already moved to Hogs and DRs for my other reg sets for that reason, but I really want to keep this reg. So, I either need to learn how to service it myself or part with it and get something else for my single tank rig which is what the D400 is dedicated to.

I understand the obscure nature of this reg.

That said I need a service manual for it. I found a schematic on frogkick but I really need some reference for the building and tuning procedures.
Regulator Saavy gives a very good overview of this center balance design but doesn't get into specifics on adjusting/tuning it.
As far as I can see there are three adjustments on the D400; The nyloc nut that sets how the fulcrum engages the poppet, the adjustment spring on top of the poppet and the rotating venturi assist.
Other than that I need some help or a real service manual, not just a schematic.
Also, not sure what the hat trick is to get the exhaust cover off, don't want to break anything doing that.

Had a typo on the thread subject line which is supposed to be Raising the White Flag ( as in I give up) if the mods want to fix it

thx

 

[Zung]

I have the manual, but it's too big to post. PM me with an email address that can take 1.7MB.

 

[halocline]

As far as I can see there are three adjustments on the D400; The nyloc nut that sets how the fulcrum engages the poppet, the adjustment spring on top of the poppet and the rotating venturi assist.
Other than that I need some help or a real service manual, not just a schematic.
Also, not sure what the hat trick is to get the exhaust cover off, don't want to break anything doing that.

Had a typo on the thread subject line which is supposed to be Raising the White Flag ( as in I give up) if the mods want to fix it

thx

I assume you're looking for help with the D400, not the MK15, right? The MK15 needs skinny circlip pliers and enough common sense to not try to remove the permanently pressed in bushing on the ambient side of the HP piston o-ring. Other than that it's very straightforward.

I'm guessing that the nyloc nut you're referring to is the little set screw that holds the lever in place, correct? (part 11011120) I usually get that screw started, just enough to hold the lever in place, then put the poppet in, adjust the spring until it stops flowing, then tighten up the set screw on the lever so that there's a bit of play, not much. You have to make sure the lever is oriented correctly as the flat spot that sits against the seat carrier isn't exactly 90o with the lever. So inserting it from one direction makes it angle a little out, from the other a little in, 'in' meaning leaning just a bit towards the mouthpiece. That's the way you want it. I think on the D400 you install the lever from the left as you're looking at the predive switch. This is the opposite of the D300 and some D350s.

The main adjustment is the little plastic internal cap (with a slot for a screwdriver) that sits on the spring. A very common problem when adjusting this is that the spring itself gets a bit twisted in the process and then as you use it, 'untwists' (there's a technical term for you) or relaxes a bit and then you have some flow. When I do it, I get an idea of where I want that pad to be, then go back and forth past that spot a few times. This should get that spring to be sitting well on the poppet. I also remove any burrs I can find on the ends of the spring (I just touch them up with sandpaper) and put a tiny bit of PTFE grease on the spring ends. that helps to keep the spring from torqueing as it gets adjusted. As a last resort, replace the spring. I'd like to find a suitable replacement spring for these 2nd stages.

If you have a later D400 with a plastic orifice, my condolences, and it would be worth looking for an older one (or D350 or 300) that has the metal orifice with that nice sharp edge.

The venturi assist flap I don't usually play around with. I leave it so that it's more or less is in the middle of it's range. Feel free to experiment!

Getting the exhaust cover off is simple but a bit of a tug. You can carefully work it off the reg body with a plastic blade or just give it a pull from one of the exhaust holes. I've had a few with pre-existing slight tears but I've never torn one. That part is tougher than you think.

By far the hardest part of rebuilding these regs IMO is dealing with the square o-ring under the dive/predive switch and the spring lever it operates. All I can tell you is have a bit of patience, don't lube that o-ring, except maybe a light dab of grease AFTER it's installed, and take some photos or draw a picture before you take it apart. The spring lever has to fit around the seat carrier in a specific way that's not easy to visualize.

Hope this helps!

 

[Scubadude_LA]

First, thanks Zung for the speedy delivery of the service guide.

Second, thanks Halocline for the in depth info on the adjustment.

Yes, the nyloc nut is the lever screw, not sure where I got 'nut" from. I did see the reference to the orientation of the lever (says to use the aspirator detent as a guide).
After looking at the service guide there are definitely some unique things to address when servicing this reg. It does talk about the tendencies for the spring twising up and to go past a bit then back off as Haloc stated. I did see the part about leaving the lever loose while adjusting the spring pressure on the poppet, then taking the slack out the lever when finished. The Viva adjustment seems fairly straight forward too. The swtich must be a royal pain because the guide says to have another switch pre-assembled with oring then install while holding pressure on the screw to keep things inline.

Mine is an earlier D400, however the exhaust cover was replaced so it looks like a later model. So I've got the good one. I managed to get the cover off earlier using soapy water. Looks like some blue locktite may have been used on the lever screw.

The problem it was having was sort of sporatic so my hunch is there is some 'twisty untwisting' type activity on the spring, technically speaking. Seems like a lever issue would be a more of a static type of issue. Just a guess.
All I've ever heard about these seconds is how hard they are to service and tune. After taking a good look at it doesn't seem too bad except for maybe the switch, don't think I'll need to mess with that now. Of course that view is subject to change this evening when I break down the reg and attempt to repair it. I'll check the hard and soft seats and take a good look at the spring then reassemble and try to retune it. I don't have a flowmeter yet but neither does the LDS so I assume a Magnehelic will be enough for the job. The lever screw should be interesting if threadlock was used. Not sure why that would be needed if the tech replaced the screw like he should have during the annual a month ago.

---------- Post Merged at 04:05 PM ---------- Previous Post was at 03:34 PM ----------

I looked up some recent parts kits for the reg and looks like the screws come with the blue threadlock on them out of the box. I guess the original design of the screw with the nylon insert has been changed.

 

[redacted]

The blue thread lock is applied by the manufacturer so not problem there. If you want to try an adjustment, loosen the set screw a bit so cracking pressure is not being effected by the set screw. Then, with air on, tighten the cap about 1/4 turn past leaking. Then it would be great to back it off to the point just before it starts leaking again - but you can't do that. So, back it off until it just starts leaking and note to position. Then tighten it up another 1/4th turn and back if off to just before the point it started leaking. With a new seat, you would want to cycle this a number of times to let everything set but should be unnecessary on a re-adjustment. Finally, readjust the set screw to just short of leaking and you should have one of the best breathing regulator made. Magnehelic is of little use unless you just need some numbers associated with great breathing. Enjoy

 

[halocline]

I've only seen the set screw with the blue anti-slip coating, and I've re-used those many times. Once or twice I went to the trouble of putting a drop of nail polish on them, but I've never seen one slip.

Once you get the hang of adjusting the spring on top of the poppet, these regs are a breeze to work on, other than the damn pre-dive lever. Thankfully, that big o-ring lasts a long time. If you reg holds a vacuum well, I wouldn't bother replacing it. The large o-ring (022) under the cap is not part of the annual kit but IME its one that gets pretty crispy. I have a feeling that the original size (mostly I've seen red ones) was not exactly 022, just a tiny bit thinner cross-section, but the 022 fits well. Sometimes you can have a bit of trouble getting the cap started straight. I'd go ahead and replace that o-ring unless the shop did it on the last rebuild.

Once they're rebuilt well they really last. I've got one that's at least three years since the last rebuild and it's holding a tune great.

 

[Scubadude_LA]

Got the D400 partially broken down. Seats look good, spring looks ok and seem to slide nicely on its surfaces but does have some sharp edges that could be softed up a bit.
Couple of things offhand that look funny:
- The tech had the aspirator opening is facing the pre-dive lever, not the mouthpiece opening. I didn't even think that was possible due to an indexing tab that is supposed to be on the aspirator which mates with a notch on the valve body.
- The second thing, which may be normal, is that the dynamic oring on the poppet is very loose and wiggles around on the popped freely, also seems very loose in when it's in the valve body. I just turned the reg over and the poppet fell out on it's own. Maybe this is normal but seems like a better fit would be needed.


I'm going to break it down completely and take a good look.
Looks like it could use a ride in the ultrasonic anyway.

 

[Scubadude_LA]

Figured I would post this incase it helps any other D400 users in the future.

The aspiratior was backward fresh out of the shop, which can be done since the valve body is symetrical except for the detent which orients the aspirator (sort of backs up the reason I want to work on these myself). Although I don't think that was the cause of the problem with the reg. Broke the reg down and did an ultrasonic cleaning since it was a little crusty then reassembled properly and adjusted it. Dove it this morning and all was well, no issues. I set the aspirator just to the point the it would not freeflow when purged. I may set it the viva to pull a little lighter, because when this thing cracks you better be ready to breath, it is really pushing some air now, almost too much.

Read suggestions above and my experience tuning it :
It reminded me of trying to sight in a rifle with a broken scope. Just when you think you have it dialed in you probably don't.
I followed the manual and combined that with the suggestions above. I would get it where I thought it was good then adjust the lever to not freeflow, then if I move the pre-dive switch around the reg would start leaking. Or I could bump it firmly against my palm and cause it to start leaking. Even after I had set the spring to just flow, then 1/4 turn in and back to just before the flow point. Also had done the back and forth movements over the intended set point to get the spring seated good. I kept playing with it and ended up about 1/2 turn tighter on the spring cap than the initial setting I found following all the suggestions, it is solid now, cracking at about 1.1 inches. Maybe my reg is a little more temperamental for some reason.
Just keep in mind, the seats had already been dived a few dive before all of this so they were broken in before I started all of this.

Thanks again for the help.

 

[halocline]

If moving the pre-dive lever gets it to start leaking, I suspect the aspirator might not be securely in place. Maybe it's loose because the genuine scubapro one-day-no-fail-seminar-factory-trained-professional installed it backwards and broke something. Is it possible that the movement of that spring over the horizontal carrier that holds the aspirator and poppet housing assembly (orifice) when you flip the dive/pre-dive switch is causing something to move with it?

I think your efforts in fine tuning it are likely slightly hampered by the fact that you've had the poppet out and now it's going back in with a different orientation to the orifice. In general I have found that these regs are a bit finicky to tune, but hold a tune very well.

 

[Scubadude_LA]

Thanks Haloc. I didn't notice anything that looked broken, unless maybe a hairline crack or something I didn't catch. By moving the switch, I was actually switching from dive to predive and vise versa then a leak would start, just figured I had the spring set too loose and the jiggling was aggrivating the poppet. I didn't take the switch and pre-dive spring apart, only removed the valve body, aspirator, spring and poppet assembly. Now you got me thinking I need to open it again an verify that the pre-dive spring, etc wasn't installed improperly at the shop at some point.
Good point on the re-orientation of the seat, hopefully it will hold a tune. When I was having the issues tuning I followed the procedures, I checked with a mag for reference and at that point it was cracking at aobut .8 even though I had followed the procedures, so on the light side. After putting a little more tension on the spring it seems solid so far. I guess I may possible have another break in on the seat to deal with though.