G260 Micro-Adjust question?

[Nemrod]

@rsingler, thanks for your thoughts. I think we are on the same wavelength.

When I am setting up a second stage of this design, this case being a G260 (but it could be a 109, 156, G250 etc), I want the lever feet to be parallel to the broach in the air tube and for that to be a neutral condition without any preload on the lever by the diaphragm and cover purge button, Scubapro asks for 2mm (purge button depression) play in the case of the G260 (I use less) for this purpose. The orifice ideally, as you indicate, should seal with just a slightest kiss of the seat. That would introduce a slight rattle in the lever but nearly imperceptible. This result ideally cannot be any other way. A bad seat and/or orifice causes us to want to run the orifice in further and further to get a seal and this can drop the lever dangerously low (affecting flow volume). Or, attacking the problem (lack of sealing due to a bad seat or orifice knife edge) from the other direction by cranking in the Micro-adjust screw to attempt to get a seal of the poppet and orifice but this now resulting in a high cracking force out of specification.

"SP wants the seal to be just a kiss at IP, with cracking effort thus determined solely by the poppet spring tension."

This sentence from your post is exactly why I think the instruction at (9) above is incorrect or incomplete. The spring force against the poppet is solely adjusted for (cracking force) tuning purposes by the Micro-adjust screw. Thus the orifice position adjustment is setting the lever height and lever play (lever rattle) and the poppet spring force adjusted by the Micro-adjust screw is setting the cracking force (the external adjustment knob being turned fully out when tuning).

I just do not see why at this point Scubapro wants me to (9) must always now readjust my orifice position. It undoes what was just done.

Without Micro-adjust, such as is the case with a 109 or a G250, the only way to adjust cracking force ultimately is to grab another poppet spring and another and another until the perfect one is found. But not everyone has a box of leftover springs. Micro-adjust is a good improvement and does make the techs life easier.

James

 

[buddhasummer]

I've read it about 10 times, getting there slowly.

 

[BoltSnap]

I've read it about 10 times, getting there slowly.

You need more pictures.

 

[Nemrod]

I am thinking the issue Scubapro is trying to address is poppet seat indention. As the seat breaks in we loose that "kiss" between the seat and the orifice and the regulator may now begin to flow. Turning the orifice in ever so slightly (1/16 turn or so) restores the seal between the poppet seat and the orifice. This minor adjustment after break in should not require further adjustment of the Micro-adjust.



I know a high volume shop cannot cycle a regulator like I do while watching a movie and then let it sit overnight under pressure before doing a final adjustment. They just set them up too stiff, high side of specification, in hopes that as the seat breaks in (indents) the regulator will be acceptable to the customer and still within specification. An experienced tech gets a feel for this I would reckon.

 

[L13]

Looking at @Nemrod 's diagram, I would think the position of the orifice (green on the right) would set the lever height. While the distance between the Micro-adjust (green on the left) and the orifice would set the preload on the spring and therefore the cracking pressure.

Unless the seat indent changes significantly with a change in the Micro-adjust, the orifice position should not need to change after a Micro-adjust change. It seems that "break in" would be a bigger effect than Micro-adjust on the ideal position of the orifice. However, after "break in", if the orifice is moved in X distance, I would expect that the micro adjust would need to move out X distance to maintain the same preload on the spring and therefore the same cracking pressure (though this change might be negligible depending on how small X is).

 

[Nemrod]

Looking at @Nemrod 's diagram, I would think the position of the orifice (green on the right) would set the lever height. While the distance between the Micro-adjust (green on the left) and the orifice would set the preload on the spring and therefore the cracking pressure.

Unless the seat indent changes significantly with a change in the Micro-adjust, the orifice position should not need to change after a Micro-adjust change. It seems that "break in" would be a bigger effect than Micro-adjust on the ideal position of the orifice. However, after "break in", if the orifice is moved in X distance, I would expect that the micro adjust would need to move out X distance to maintain the same preload on the spring and therefore the same cracking pressure (though this change might be negligible depending on how small X is).

Yes, I think you are exactly right, that is what I am saying. However, the orifice adjustment needed after break in (of a good seat and orifice) is very small, like 1/16 turn, so while you are correct in that a similar adjustment could be done to the Micro-adjust, in practice it just is not needed. Unless of course gross adjustments are needed and at that point we need to be looking at the (possibly cut) seat and orifice knife edge closely for a defect.

To follow Scubapro's procedure, which is surely incomplete, to readjust the orifice when the Micro-adjustment is set, we could chase our tails forever, like walking halfway to a wall and then halfway again we would spend infinity before getting there. I am of the position that once we have our lever set via orifice adjustment to get that just enough kiss to stop flow post break in (more ideal) or via experience prior to break in (less ideal) and then set our Micro-adjustment per the manual then we need not readjust the orifice or go back and forth with these two adjustments. After the LP seat is indented and the orifice final adjustment made compensating for seat break in a readjustment of the Micro-adjust screw just is not needed, again in practice, and we can call the job done.

I generally set the orifice on my regulators, post break in to slightly free flow with the adjustment knob fully out. I usually have to turn it in a half to a full turn to stop free flow. On the 109/156/G250 sort of becomes a seat saver in effect and reduces cracking force too near zero for those times you might really want to honk on your reg!

 

[L13]

Yes, I think you are exactly right, that is what I am saying.

I'm glad we agree on that. It means I might actually understand how it works.

I generally set the orifice on my regulators, post break in to slightly free flow with the adjustment knob fully out. I usually have to turn it in a half to a full turn to stop free flow.

I like this idea.

 

[rsingler]

@Nemrod has it right.

However, after "break in", if the orifice is moved in X distance, I would expect that the micro adjust would need to move out X distance to maintain the same preload on the spring and therefore the same cracking pressure (though this change might be negligible depending on how small X is).

Theoretically, that's correct, after seat set has occurred. In practice, however, seat indentation is functionally equivalent to having the orifice unscrewed by the depth of the indentation. Cracking effort falls, and you either now like that (because the shop set things up stiff), or the reg begins to freeflow, and you need a bit more spring tension via the microadjust.

When I am setting up a second stage of this design, this case being a G260 (but it could be a 109, 156, G250 etc), I want the lever feet to be parallel to the broach in the air tube and for that to be a neutral condition without any preload on the lever by the diaphragm and cover purge button, Scubapro asks for 2mm (purge button depression) play in the case of the G260 (I use less) for this purpose. The orifice ideally, as you indicate, should seal with just a slightest kiss of the seat. That would introduce a slight rattle in the lever but nearly imperceptible. This result ideally cannot be any other way. A bad seat and/or orifice causes us to want to run the orifice in further and further to get a seal and this can drop the lever dangerously low (affecting flow volume). Or, attacking the problem (lack of sealing due to a bad seat or orifice knife edge) from the other direction by cranking in the Micro-adjust screw to attempt to get a seal of the poppet and orifice but this now resulting in a high cracking effort out of specification.

"SP wants the seal to be just a kiss at IP, with cracking effort thus determined solely by the poppet spring tension."

This sentence from your post is exactly why I think the instruction at (9) above is incorrect or incomplete. The spring force against the poppet is solely adjusted for (cracking force) tuning purposes by the Micro-adjust screw. Thus the orifice position adjustment is setting the lever height and play (rattle) and the poppet spring force adjusted by the Micro-adjust screw is setting the cracking force (the external adjustment knob being turned fully out when tuning).

I just do not see why at this point Scubapro wants me to (9) must always now readjust my orifice position. It undoes what was just done.

Without Micro-adjust, such as is the case with a 109 or a G250, the only way to adjust cracking force ultimately is to grab another poppet spring and another and another until the perfect one is found. But not everyone has a box of leftover springs. Micro-adjust is a good improvement and does make the techs life easier.

James

Yes, James. We're thinking the same about this.
For those reading along, this discussion revolves around the one shortfall in the G250 and ALL its kin (and there are many): the seeming requirement to tune the reg with the adjustment knob all the way out. It wasn't always this way. Sherwood, who has been making regulators longer than Scubapro, delivered regs that deliberately freeflowed with the knob all the way out. This is from the 1998 Maximus service manual. Note the second sentence in step 5.5 A.1.:

And they even have a section on checking exhalation effort!
Divers weren't as clueless back then. You expected a freeflow; adjusted it away and picked your cracking effort, as low as 1.0" static and .75" dynamic due to Venturi assist!

But now, every barrel reg without a microadjust has you set it up with the knob in the minimum resistance position. If cracking effort is too low, many manuals tell the tech to screw in the orifice to raise spring tension. This is positively, absolutely wrong, because it begins to drop the lever, impairing maximum valve opening. Your comment above about having regs that freeflow with the knob out fully is exactly right.
Once the seat seals to the orifice at IP with "some" level of spring tension, you shouldn't mess with orifice position any more (and we can quibble about Scubapro's recommended slight readjust after determining your desired cracking effort). Anything else risks dropping the lever, which can be fatal at high gas density (think Air at 120' fighting a current).
At this point, you should adjust your cracking effort with your knob, just like Sherwood taught. If you can't get a high enough cracking effort without using up most of your knob range, you need to shim the spring or get a new spring. If your cracking effort is too high with the knob out all the way, you're stuck with a pig of a regulator.
Having a microadjust changed all that. Now the knob (fully out) is actually in a sort of "mid position", due to the protruding nub of the microadjust. You adjust your orifice and then go in or out with the micro to set spring tension.
But all of this presumes that the lever foot is not floating, but jammed up tight against the square broach in the barrel. Once a dull orifice knife edge or a flawed seat requires extra pressure from the spring to seal, it's very tempting to screw the orifice in more to seal. As suggested above, this is a very dangerous practice due to the secondary effect on lever height. Instead you should screw in the adjustment knob (or microadjust) a bit to provide more spring tension for the seal. You'll have less knob range if you need to adjust the reg for giant stride or octo use, and the reg will freeflow if you unscrew it fully, but at least your lever retains maximum excursion.
If your reg case requires lever drop to avoid triggering the valve when you screw down the faceplate, that's a design flaw in a barrel reg, IMO. Now the lever foot is displaced away from the broach, and seat indentation over time will cause freeflow not just because the spring is relaxing as the poppet moves toward the orifice, but because the lever will want to rise, but is constrained by the diaphragm, and the valve opens. In the old days, @herman made us a tool to actually safely bend the lever feet so the lever had optimum position.

That's no longer accepted practice. Instead, manuals (including Scubapro) set a desired lever height to fit inside the case, and as this topic originally discussed, any change to spring tension via the microadjust should optimally require orifice reset (which removes part of the change you just made to the microadjust!) until you iteratively end up with
1) the desired change to cracking effort
2) minimum seat pressure to seal
3) maximum lever excursion.
And 3) should be done pressurized.
But as you pointed out, @Nemrod, that iterative process can have you chasing your tail forever, lol!

NONE of this is taught to service techs at mfr seminars, so it's not surprising that there are so many dangerously rattling levers and stiff breathers.

 

[Nemrod]

@rsingler, thanks for the rest of the story. Yes, yes, indeed. I have seen plenty of incorrectly adjusted levers too high and especially too low which can be dangerous. Thanks again, great post!

For entertainment, here is the SP G250V which does not have the Micro-adjust as does the G260:




This G250 diagram shows the ideal position of the feet of the lever in the barrel broach, parallel to the cut face (exactly 90 degrees to the barrel):




Then imagine if the lever is lowered by running the orifice inward to the barrel, to attempt to stop a leaking (damaged?) orifice/seat, that a dangerous condition would be created. It can also be seen that when the seat indents during break in that the lever will rise exacerbating the issue as the diaphragm will now be preloading the lever and opening the valve further, exactly what is not wanted.

 

[Bob DBF]

You need more pictures.

I always need more pictures.