D420! How about that?

[rsingler]

Fine tuning without a Magnehelic
Would it be ok to press down the purge flap and turn allen bolt counter clockwise till it starts leaking air when I pressurize the stages?

Lets say I turn it clockwise till it stop leaking - would that be the same while diving?

Asking because plunging water in water and pressure may have an impact

That's the first half. That seals the valve but doesn't tell you cracking effort. You can check that in a bowl of water, holding the diaphragm parallel to the water and immersing it slowly until it begins to hiss. Here's a short except from a recent seminar, taken wholly out of context, that sort of shows how to do it...
The distance from the diaphragm disc to the surface is your cracking effort of inches of water, and it should be 1.2-1.4" for the D420. It doesn't tolerate being tuned hot because the diaphragm is lower on the water than standard case designs. That means it breathes poorly out of the water, but that all goes away when submerged.

And all this depends upon the factory having left a tiny gap between the back of the diaphragm and the lever. Otherwise there's a physical linkage all the way from the "allen bolt" on top, through the poppet, onto the lever and against the diaphragm. When that gap isn't present, increasing spring pressure with the hex fitting doesn't do anything and tuning is unstable. They only modified the service manual to reflect that requirement this year, though we've known it awhile now.
You can check that by pushing out the hinge pin holding the purge lever and removing the lever. Now you can see the diaphragm. With the reg pressurized, tap lightly on the center disc and make sure there's a half millimeter of clearance. If not, adjusting gets a little more complicated...

 

[hedonist222]

I don’t use a magnehelic, the @James79 adjuster helps with fine tuning, the tuning guidelines in this post will get you most of the way there.

There's 101 pages
I've gone through 45....

 

[hedonist222]

That's the first half. That seals the valve but doesn't tell you cracking effort. You can check that in a bowl of water, holding the diaphragm parallel to the water and immersing it slowly until it begins to hiss.
The distance from the diaphragm disc to the surface is your cracking effort of inches of water, and it should be 1.2-1.4" for the D420. It doesn't tolerate being tuned hot because the diaphragm is lower on the water than standard case designs. That means it breathes poorly out of the water, but that all goes away when submerged.

And all this depends upon the factory having left a tiny gap between the back of the diaphragm and the lever. Otherwise there's a physical linkage all the way from the "allen bolt" on top, through the poppet, onto the lever and against the diaphragm. When that gap isn't present, increasing spring pressure with the hex firing doesn't do anything and tuning is unstable. They only modified the service manual to reflect that requirement this year, though we've known it awhile now.

Would love to send it to you but I'm all the way I'm the UAE.

Based on my second post, can I incrementally back it (clockwise), till it stops free flowing when submerged?

 

[rsingler]

I wouldn't do it submerged.
I would incrementally add clockwise 30° increments and  then submerge to the point of valve opening (hiss), checking after each adjustment until the center disc of the diaphragm is 3cm deep in your sink.

Or conversely, UNscrew counterclockwise in 30° increments if your valve doesn't open until deeper than 3cm.

 

[jakehbk]

That means it breathes poorly out of the water, but that all goes away when submerged

That was my chief complaint against the reg. Is there ANY way to get it to breath at least passably while I'm huffing and puffing up my dive ladder? My S600 and G250 just don't seem to care where they are.

 

[rsingler]

Unfortunately not...

But there may be a mistuning issue if you find it that noticeable.
My G250's are tuned to 1.0-1.1"
My D420's are tuned to 1.2-1.4"
In the water the D420's beat the G's by a mile.
Out of the water, it's a pretty small difference.

It all has to do with the fact that with its case shape, the D420 diaphragm is a half inch lower in the water than the G250 in the standard diving position.

 

[hedonist222]

And all this depends upon the factory having left a tiny gap between the back of the diaphragm and the lever. Otherwise there's a physical linkage all the way from the "allen bolt" on top, through the poppet, onto the lever and against the diaphragm. When that gap isn't present, increasing spring pressure with the hex firing doesn't do anything and tuning is unstable. They only modified the service manual to reflect that requirement this year, though we've known it awhile now.
You can check that by pushing out the hinge pin holding the purge lever and removing the lever. Now you can see the diaphragm. With the reg pressurized, tap lightly on the center disc and make sure there's a half millimeter of clearance. If not, adjusting gets a little more complicated...

Thanks Rob and others.

There is some clearance.

 

[jakehbk]

Unfortunately not...

But there may be a mistuning issue if you find it that noticeable.
My G250's are tuned to 1.0-1.1"
My D420's are tuned to 1.2-1.4"
In the water the D420's beat the G's by a mile.
Out of the water, it's a pretty small difference.

It all has to do with the fact that with its case shape, the D420 diaphragm is a half inch lower in the water than the G250 in the standard diving position.

Those were my settings as well, at least for the D420. My G250 is probably in that ballpark as well. I wouldn't say mine blew the other regs out of the water while being underwater. It felt fine. But the surface breathing for me was very noticeable. I like to keep my reg in my mouth until I have 2 feet on solid boat deck and I was ending each dive on a sour note of rough breathing.

I ended up putting my evertrustworthy S600 on my shiny new MK19evo.

 

[scrane]

Just cracking at 1.4 shouldn't be that big a problem. Is there something else going on?

 

[jakehbk]

Just cracking at 1.4 shouldn't be that big a problem. Is there something else going on?

Couldn't tell ya. Maybe I'm hyper sensitive to the change for whatever reason. Underwater I didn't really feel anything remarkable in the breathing. I'd just as happily breathe from my G250 as I would the 420. But for me each dive was like a good movie with a bad ending.

Doesn't matter too much tho. I mainly bought the reg set for the MK19evo anyway. This was before it was sold ala carte.