D420! How about that?

[rsingler]

As an interesting aside to the poppet modification discussed above, I discovered another wrinkle in D420 tuning.

When I tuned my D420 with the new seat, I was moving quickly and left the pressure on the regulator. I adjusted the lever for the tiniest bit of "tap-tap" space between the diaphragm disc and the lever and then screwed the faceplate on. I had a tiny bit of freeflow and started screwing down the hex fitting on top of the poppet spring. But it took way more than I expected to seal. And I couldn't get 0.5" cracking.

I took the purge lever back off, and to my surprise, I didn't have any "tap-tap" space! WTH? I'd just adjusted it!
What happens is that when you screw down the faceplate, the white anti-friction ring (#41) that prevents the edge of the diaphragm from rolling has a smaller inner diameter than the faceplate. What that does is puts pressure on the slope of the diaphragm as it rises from the edge, and pulls down on the center disc. That removed the play between diaphragm and lever, and recreated all the instability we struggled with when this reg first came out.

Solution?
First, do your initial adjustment of lever height with pressure off, because the lever drops slightly more when the pressure comes on.
Second, after you put on the faceplate, and before you add the purge lever, make sure there's still a little "tap-tap" space between the diaphragm disc and the lever. Now you can tune with the top hex alone.

As a quick lever adjustment check, the lever should be barely visible sighting across the case rim, with the reg pressurized. That should give you the space you want between lever and diaphragm. That also means your reg will rattle ever so slightly with pressure on. It should rattle less, or not at all, with pressure off.

 

[lexvil]

Just did 2 long dives with the 420/104 ala Kupu, over 3 hours on the reg and still holding tune, about 1” cracking but in the water there isn’t any noticeable effort, really incredibly smooth. I’ll probably put another 10-15 hours on it before opening it up to look at the seat.

 

[jakehbk]

Question for those that have dove the D420 in real world conditions, and even more appropriate if you've dove it with a dpv on doubles or as an octo.

How sensitive is this reg out of the mouth? How prone is it to free flows? Usually not having a breathing adjustment is a no go for me on 2nd stages. I hunt lobster on a dpv and with independent doubles so being able to crank down on the reg that's not in my mouth helps greatly with controlling free flows when it gets knocked around. I've even had to adjust going headfirst into a current on my dpv.

Any of you early adopters have input on these types of scenarios? Is the purge lever/button stiff enough to stay put going head long into a current? Is the pre dive switch enough to stop free flows if the reg is bumped around outside the mouth? If anyone's run it with a necklace, is it awkward because it's a slightly taller 2nd stage?

 

[rsingler]

I ran it as my bailout reg on a necklace for CCR training in Florida. Tuned to 1.2" there were no freeflows. I put the lever in pre-dive for giant stride but otherwise left it in normal. With multiple boom drills back and forth between loop and necklace, I had zero freeflow issues.

I'm not a scooter guy, so no first hand experience. Initially, I was worried because the purge lever is so big. But it turns out that both as a primary and on a necklace, the tail of the lever lies almost horizontal in scootering position, so I just don't think it'll be a problem. Pressure on the upper part of the lever does nothing because of the hinge and spring.

 

[lexvil]

An update on my “simon” 420, I have been using this reg almost exclusively for 20 months or so, last week I noticed a stream of bubbles on inhale

I’ve had this reg opened many times as I worked with the modified seat, never messed with the o rings, so this morning I decided to rebuild it back to factory specs, took it apart but it’s so cold in my shop I decided to finish up in the dining room
didnt take a lot of pictures

I decided to use the factory seat since some of the newer 420’s seemed to behave better than these early ones did, now the we have the tuning down, I’ll dive it this weekend if all goes well, right now it’s rebuilt and adjusted and sitting under pressure.

 

[Couv]

Thanks for the update. Did you find the source of the bubbles?

What is this?

 

[lexvil]

Thanks for the update. Did you find the source of the bubbles?

What is this?

I didn’t specifically but the notch in that oring actually seems to be an artifact in the picture, I don’t see it in the old oring. That is one of the few moving parts in the 420 but it doesn’t move far when moving from dive to pre dive. I was leaning toward the 3 seals in that area #’s 28, 30 & 34 since those are the only points in the assembly that can leak there. Don’t know for sure yet until I dive it again, if I get the same leak I’ll have to go over it closely and see if there is a crack in something.


edit; looking closely at the picture, that is the new #30, it has a white paint spot on it that the old one doesn’t

from another kit

 

[350xfire]

The only great feature of this reg is the ability to switch from left to right hose location without any reconfiguring other than hose removal and plug removal. The service kit for this thing is upwards of $70 since it contains a large part that gets replaced every service. I've serviced a couple and I can't say they are so amazing that I need to go get one. Cool odd looking reg though.

 

[hedonist222]

Is it normal for it to make a honking sound when inhaling quickly outside of water?

 

[buddhasummer]

It's not uncommon. Some do, some don't. It's normal.

*** I mean some second stages do and some don't, IIRC my D420 fluttered.