G260 Micro-Adjust question?

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Nemrod

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Not exactly a newb to regulator innards but this is my first Scubapro product with the Micro-Adjust feature. The manual says this:



It is my opinion that the "MUST" should read MUST NOT as otherwise readjusting the orifice undoes the Micro-Adjustment that I just did? The way I see it is that with the Micro-Adjust at a neutral position per the MM and the adjustment knob fully out we adjust the orifice to get lever height correct and I usually set my regs to just barely, ever so lightly, flow when the knob is fully turned out. Once a new seat on the poppet is broken in and takes a set I then use the Micro-Adjust to back poppet spring tension down until I get 1.0-1.2 inches on my Magnehelic (and again with the knob fully out, a very slight, almost imperceptible free flow).

Anyways, if I follow the Scubapro MM my G260 breath like (insert popular name for excrement here) and if I do it my way they breath almost as good as a G250 or a lowly AL Core :wink:.

Is Scubapro full of (excrement)?

My brand new and hardly dived Mark 17 Evo had a loose yoke retention nut! Might want to apply the correct torque per your MM Scubapro! If that happens in use more (excrement) happens o_O. Just saying :).

James
 
Pretty sure I agree with you, once lever height is set I wouldn’t mess with it just because the spring tension was adjusted.
 
I never play with orifice again once lever height is set. I've never had any issues doing it this way. I used to follow manual but it just increased tuning time and netted same results as not re adjusting orifice.
 
Ever buy a SP second stage that was in spec? I've bought around 14 and not one was in spec as per SP, not one. Every one has been cracking over 2" and in some cases almost 3". My guess is they don't really bother and simply put the onus on the dealers to tune before sale (?)
 
Ever buy a SP second stage that was in spec? I've bought around 14 and not one was in spec as per SP, not one. Every one has been cracking over 2" and in some cases almost 3". My guess is they don't really bother and simply put the onus on the dealers to tune before sale (?)
What better way to appear as a “magic” tuner than to start out needing tuning.
 
the dealers to tune before sale

The dealer should be doing that with any regulator and all brands. That's what I have always done. I do a basic regulator check including IP and cracking pressure checks before the regulator kit is handed over to the client. I put a $$$ value to this service and offer it for free to my customers who bought their kit from me but I charge somebody who comes through the doors wanting their kit to be put together and checked if they bought it from somebody else.
 
A G260 view below:


I have purchased new several AL regulators and they were all fine and in specification and performed well out of the box. The only SP regulators I have bought new (since sometime about in the mid 70s) is a G260 set and it performed as if it had a cardboard diaphragm. Tuning it per the manual, with the exception of the reason for this thread, resulted in a fine performing regulator, like I said, nearly as good as a G250 or an AL Titan LX/Core/Helix :wink:.

I bought this Titan LX circa 2004. It worked perfectly from first dive until now and has never been adjusted or messed with or rebuilt. It has many dives on it and it breaths great and is my most reliable regulator ever. When in doubt, I grab it to dive:



But the Titan LX above is about to get a full rebuild and then it will take number 2 position behind my new G260/Mark 17 Evo now residing in pole position.

James
 
It is my opinion that the "MUST" should read MUST NOT as otherwise readjusting the orifice undoes the Micro-Adjustment that I just did?
@rsingler
 
@Nemrod has a point. But it's complicated.

In a perfect world, the perfect lever foot sits flat up against the orifice side of the square lever broach in the barrel (green box in pic below), and the perfect lever arm is shaped to almost kiss the back of the diaphragm disc when under pressure. Confirm that Scubapro wants this with their step 10. above.
In this configuration, the orifice knife edge has depressed the face of the seat enough to create a seal without pushing the poppet towards the balance chamber enough to allow the lever to fall away from the broach side.
_IMG_000000_000000.jpg

That commonly happens with less sophisticated designs, where the service manual specifies, e.g., "Screw in the orifice until the lever is 2mm above the case rim."
So in SP's ideal world, the poppet almost doesn't move. The seat is a little more compressed when unpressurized (hence the seat saver in the purge button) if the lever foot doesn't trap the poppet, but then tries to move fractionally away from the orifice when IP is applied, though not enough to unseal. Therefore, there's almost no point in re-seating the knife edge after 1/4 turn on the micro-adjust.

But Scubapro's position is that (especially in those cases where the lever foot is not held right against the lever broach by the poppet), increasing the spring tension (even in a "micro" way) slightly increases the indentation of the orifice knife edge into the seat. SP wants the seal to be just a kiss at IP, with cracking effort thus determined solely by the poppet spring tension. When the lever requires some tiny drop to fit under the diaphragm disc without having the valve opened by the cover when it's screwed on, the orifice/seat interface "floats", with its position in the square broach governed solely by the interplay between seat compressibility and poppet spring tension.
Whether the interface position floats or is right against the side of the lever broach, unless you are absolutely diligent about using the G260's purge button seat saver after every dive day, you'll quickly put a slight permanent indentation in the seat, which is equivalent to backing the orifice out a hair, and the reg's cracking effort will drop. If you tune hot to start, that may result in a tiny bubbling freeflow.

We're really splitting hairs here. The thread pitch of most brands' micro-adjusts is 1/2 to 2/3 of the orifice (sorry, can't open up my G260 just yet, to check). The thread pitch of a Scubapro orifice is about 0.675mm/turn. My "standard" extra 1/12 turn after sealing the orifice adds less than 0.05" to cracking effort, and moves the knife edge in 0.05mm. A quarter turn on the micro adjust to raise cracking effort pushes back about 0.1mm. So backing out the orifice and resealing it will remove about half of that correction. If you need to raise cracking effort significantly (like 0.4") then you might see much more indentation of the seat, and it makes sense to reseat the orifice, which may remove 25% of your correction.
So tuning will be an iterative process designed to minimize pressure on the LP seat to the minimum required for your cracking effort. But with most regs that have a slightly dropped lever, the floating interface inside that square broach means that you end up in the same place in the end, and @Nemrod is right.
 

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