Suspense is killing me... What was the issue?
A change of heart, Scubapro D420
- Thread starter lexvil
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Of course! Your frustration was completely justified if you followed the service manual to tune it, because it's my opinion that the manual is flat out incorrect. Tuning it their way ADDS to the instability.
- Messages
- 17,253
- Reaction score
- 9,449
- Location
- Somewhere between here and there
- # of dives
- 2500 - 4999
From Rob PT1:
"Okay, guys, I have an answer of sorts.
First, your reg is now performing well, below spec, with no freeflow or instability.
Hooray!
Second, I believe that Scubapro has some great engineers who just don't communicate very well with the marketing department.
What did I find?
No nicks in the orifice. No crack in the spring plate (it's a mold mark). No flaw in the seat.
After taking it apart, it was my plan to throw in the new parts from the included kit and tune it up. But I realized that wouldn't teach us anything.
So on camera, I fiddled with the seat and the orifice. The seat looks like firm memory foam. It takes a dent with even a gentle touch from a brass pick, and that dent takes hours to recover. The good news is that it should conform to any orifice perfectly. However, the "memory" in the memory foam composition was a red herring for me, as I thought that if the poppet shifted rotational position after sealing against a flawed orifice, it might leak until the seat material recovered. But I think that isn't the problem.
The orifice is interesting. Under 30x mag, the "knife edge" is marginally uneven, like a cobblestone street. It's a function of the molding process. So I tried to improve it. But using Micromesh 4,000 and 6,000 didn't do a thing! Not a visible thing! I tried the pencil eraser trick next, even though I think that's usually too rough. But that didn't do anything, either. That's one tough polymer.
I next tried "preimprinting" the seat by applying pressure with it to the knife edge before assembly. I don't think that did anything either, because of what I subsequently found.
So I re-assembled it with all the old parts, and found that the seat sealed at 0.5"!! The memory foam truly must conform to the knife edge cobblestones.
But when the diaphragm went on, with the lever at the nominally correct height, it was freeflowing until I screwed the top hex adjuster in ALL THE WAY! At that point, I figured it was 1.6" or more, and was ready to swap out to new parts. But when I measured it, it was only 0.8" and I had no more spring pressure to apply! The hex was in all the way!
So I checked the lever/diaphragm interface once more, and the lever was tight up against the diaphragm disc with the pressure on. I thought that perhaps when things settled in after multiple purges, things shifted subtly. Turns out that was wrong, too.
Anyway, that's when the light bulb went on. All the instability was due to preloading of the valve by the blue elastic diaphragm!
When I dropped the lever until there was 1/4mm of light "tap-tap" distance before the diagram disc contacted the lever with pressure OFF, then there was 1/2-3/4 mm when the reg was pressurized.
With that, the reg sealed right up, and I kept backing the top hex out until it was 0.8". Still no leak.
And that's the key. The Service Manual advice to use the lever screw to adjust cracking effort after initial tuning is wrong, Wrong, WRONG.
[EDIT: I've since learned that the manual isn't wrong. I misread the translation from the Italian. It's just very cryptic. It does not suggest that you tune with the lever hex. My mistake. Apologies to Scubapro, whom I must seem always ready to criticize.]
Start with the lever co-planar with the case. Start with the top hex all the way out. Reassemble the reg and confirm that there's a hint of "tap-tap" between the lever and diaphragm disc. If not, unscrew the lever hex a touch and drop the lever another mm at a time. Pressurized, the reg will probably hiss. Add spring pressure with the top hex until it seals. Now start tuning with increasing spring pressure until it reaches 1.2". That cracking effort is fine, because it means a true effort of 0.4" in the standard diving position with the diaphragm lowest (due to case geometry fault). You could trim down to 0.8" like I did in the Keys. But that means zero effort on inhalation underwater and EASY freeflow if you're not meticulous when removing the reg.
Anyway, the short answer is:
1) the new orifices are fine
2) the new seat material seals very well
3) the spec of 1.2" isn't what it seems
4) this reg really blows some air!
5) the diaphragm/poppet spring balance is critical
Corollary of #3: doing the usual SB thing of tuning below spec has consequences with a reg that delivers so much air over such a short path."
"Okay, guys, I have an answer of sorts.
First, your reg is now performing well, below spec, with no freeflow or instability.
Hooray!
Second, I believe that Scubapro has some great engineers who just don't communicate very well with the marketing department.
What did I find?
No nicks in the orifice. No crack in the spring plate (it's a mold mark). No flaw in the seat.
After taking it apart, it was my plan to throw in the new parts from the included kit and tune it up. But I realized that wouldn't teach us anything.
So on camera, I fiddled with the seat and the orifice. The seat looks like firm memory foam. It takes a dent with even a gentle touch from a brass pick, and that dent takes hours to recover. The good news is that it should conform to any orifice perfectly. However, the "memory" in the memory foam composition was a red herring for me, as I thought that if the poppet shifted rotational position after sealing against a flawed orifice, it might leak until the seat material recovered. But I think that isn't the problem.
The orifice is interesting. Under 30x mag, the "knife edge" is marginally uneven, like a cobblestone street. It's a function of the molding process. So I tried to improve it. But using Micromesh 4,000 and 6,000 didn't do a thing! Not a visible thing! I tried the pencil eraser trick next, even though I think that's usually too rough. But that didn't do anything, either. That's one tough polymer.
I next tried "preimprinting" the seat by applying pressure with it to the knife edge before assembly. I don't think that did anything either, because of what I subsequently found.
So I re-assembled it with all the old parts, and found that the seat sealed at 0.5"!! The memory foam truly must conform to the knife edge cobblestones.
But when the diaphragm went on, with the lever at the nominally correct height, it was freeflowing until I screwed the top hex adjuster in ALL THE WAY! At that point, I figured it was 1.6" or more, and was ready to swap out to new parts. But when I measured it, it was only 0.8" and I had no more spring pressure to apply! The hex was in all the way!
So I checked the lever/diaphragm interface once more, and the lever was tight up against the diaphragm disc with the pressure on. I thought that perhaps when things settled in after multiple purges, things shifted subtly. Turns out that was wrong, too.
Anyway, that's when the light bulb went on. All the instability was due to preloading of the valve by the blue elastic diaphragm!
When I dropped the lever until there was 1/4mm of light "tap-tap" distance before the diagram disc contacted the lever with pressure OFF, then there was 1/2-3/4 mm when the reg was pressurized.
With that, the reg sealed right up, and I kept backing the top hex out until it was 0.8". Still no leak.
And that's the key. The Service Manual advice to use the lever screw to adjust cracking effort after initial tuning is wrong, Wrong, WRONG.
[EDIT: I've since learned that the manual isn't wrong. I misread the translation from the Italian. It's just very cryptic. It does not suggest that you tune with the lever hex. My mistake. Apologies to Scubapro, whom I must seem always ready to criticize.]
Start with the lever co-planar with the case. Start with the top hex all the way out. Reassemble the reg and confirm that there's a hint of "tap-tap" between the lever and diaphragm disc. If not, unscrew the lever hex a touch and drop the lever another mm at a time. Pressurized, the reg will probably hiss. Add spring pressure with the top hex until it seals. Now start tuning with increasing spring pressure until it reaches 1.2". That cracking effort is fine, because it means a true effort of 0.4" in the standard diving position with the diaphragm lowest (due to case geometry fault). You could trim down to 0.8" like I did in the Keys. But that means zero effort on inhalation underwater and EASY freeflow if you're not meticulous when removing the reg.
Anyway, the short answer is:
1) the new orifices are fine
2) the new seat material seals very well
3) the spec of 1.2" isn't what it seems
4) this reg really blows some air!
5) the diaphragm/poppet spring balance is critical
Corollary of #3: doing the usual SB thing of tuning below spec has consequences with a reg that delivers so much air over such a short path."
- Messages
- 17,253
- Reaction score
- 9,449
- Location
- Somewhere between here and there
- # of dives
- 2500 - 4999
From Rob PT2:
"And I'm STILL discovering things!
To wit:
I was just now putting my own reg back together, following the steps I just outlined above. I had my tap, tap, and then pressurized the reg. Hissing lightly, as expected, so I started tightening up the top hex.
I got it where I wanted (1.2") and then decided to back it down a little to test the seal. It was unstable again!
When I tap, tapped, there wasn't one! Where did it go? I'd already set the lever. But the clearance was gone.
Time for one more light bulb:
When I increased spring pressure via the top hex, the seat compressed a bit, the poppet dropped a bit, and the clearance to the lever disappeared! Now, the assembled diaphragm was contributing.
So I left the top hex alone, took off the diaphragm, and dropped the lever a second time. The cracking effort went UP, as full spring pressure came to bear against a poppet that had been held in check by the diaphragm.
Now it's stable again, and responding to the hex screw alone.
SOOO....
I guess the manual isn't completely wrong. They just didn't tell you why you have to go back and adjust the lever when it doesn't tune out. It's not to adjust cracking effort, though that does in fact happen. It's to relieve the added tension contributed by the diaphragm, and restore the ability of the top hex screw to smoothly change poppet spring pressure. But the manual doesn't tell you to go back to step 1 (top hex). They only say to adjust lever height. And that's incomplete as a procedure."
"And I'm STILL discovering things!
To wit:
I was just now putting my own reg back together, following the steps I just outlined above. I had my tap, tap, and then pressurized the reg. Hissing lightly, as expected, so I started tightening up the top hex.
I got it where I wanted (1.2") and then decided to back it down a little to test the seal. It was unstable again!
When I tap, tapped, there wasn't one! Where did it go? I'd already set the lever. But the clearance was gone.
Time for one more light bulb:
When I increased spring pressure via the top hex, the seat compressed a bit, the poppet dropped a bit, and the clearance to the lever disappeared! Now, the assembled diaphragm was contributing.
So I left the top hex alone, took off the diaphragm, and dropped the lever a second time. The cracking effort went UP, as full spring pressure came to bear against a poppet that had been held in check by the diaphragm.
Now it's stable again, and responding to the hex screw alone.
SOOO....
I guess the manual isn't completely wrong. They just didn't tell you why you have to go back and adjust the lever when it doesn't tune out. It's not to adjust cracking effort, though that does in fact happen. It's to relieve the added tension contributed by the diaphragm, and restore the ability of the top hex screw to smoothly change poppet spring pressure. But the manual doesn't tell you to go back to step 1 (top hex). They only say to adjust lever height. And that's incomplete as a procedure."
- Messages
- 17,253
- Reaction score
- 9,449
- Location
- Somewhere between here and there
- # of dives
- 2500 - 4999
For selfish/pride/ego reasons:
PT3
"Feel free to quote the results!
I'll try to put the two simultaneous cameras into a video shortly. I'll send it to you two and you can decide if it can be released.
Hardly your error, Simon. It took me a couple hours of pondering to realize what was going on. And that the manual specified the exact opposite didn't help at all!"
PT3
"Feel free to quote the results!
I'll try to put the two simultaneous cameras into a video shortly. I'll send it to you two and you can decide if it can be released.
Hardly your error, Simon. It took me a couple hours of pondering to realize what was going on. And that the manual specified the exact opposite didn't help at all!"
- Messages
- 17,253
- Reaction score
- 9,449
- Location
- Somewhere between here and there
- # of dives
- 2500 - 4999
axxel57
Contributor
Can't wait to get one of the D420s in my hands....
Good job from Rob as usual!
Most of the SP Manuals which have been published after the ones from Pete Wolfinger have been pretty lousy and sometimes even confusing, that's the reason I don't use them in my practical work on regs.
To me it seems they cost me more time than they save me.
It's sad that other manufacturers seem to have improved their repair manuals by learning from the well made SP Manuals from the early 90s, while SP seem to have orientated their manuals on the others manufacturers manuals from the 80s and 90s......
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