ScubaPro G-500

[Rusty Shackleford]

It's not terrible now but both of my currently used G-250s. One HP(but with a brass air barrel and just marked G-250) and one not, both beat it slightly in breathing effort.

 

[rsingler]

Playing with the balance chamber, I guessed it was a way to adjust cracking pressure independent of the lever height and that was it's true purpose.

Almost exactly right. The balance chamber adjustment is a way to adjust cracking pressure independent of the orifice's sealing position. What is desired is to use the minimum pressure on the orifice-LP seat interface, to keep from grooving the seat excessively. All you want is what will seal. THEN, add spring tension with the balance chamber adjustment to give you the cracking effort you want. As a secondary issue, just as you said, it adjusts cracking effort independent of the lever height, so the end result is the same. However, the benefit as you figured out is that you can have optimum lever height (and thus maximum valve opening on inhalation) with fully adjustable cracking effort.

With the old G250, if getting a seal and correct cracking effort dropped the lever excessively, then the lever would rattle (the tell-tale sign) and the valve wouldn't open as widely as it should. The only solution was to bend the legs. Often though, the problem was the opposite: the spring tension would be too LOW, and the washer would give you adequate cracking effort without screwing in the lever past minimum seal and dropping it. But when all else failed, you just had to bend the feet to get the lever 1/32" under the diaphragm when pressurized at the cracking effort you wanted.
Hence: Scubapro finally did what they did long ago with the S600, and created the G260.

 

[rsingler]

It's not terrible now but both of my currently used G-250s. One HP(but with a brass air barrel and just marked G-250) and one not, both beat it slightly in breathing effort.

You can quantitate that with a kitchen sink cracking effort measurement. (Again, pardon me if you already know this, or have your own magnehelic)
Hold the pressurized reg so that the mouthpiece is up and the diaphragm is horizontal. The seam between the faceplate and the reg case is a rough zero point.
Slowly dip the reg into a sink full of water, immersing it gradually until it just begins to hiss. The distance from the surface of the water down to the faceplate seam is the cracking effort that you'd measure on a magnehelic.
You can compare the two regs easily that way, unless the cracking effort is so high that the mouthpiece drops below the surface before the valve hisses. In that case, your cracking effort is over about 2", or whatever the vertical distance is from the faceplate seam to the mouthpiece.

 

[Rusty Shackleford]

Even all the way out, it did not appear to be quite touching the diaphragm.

 

[rsingler]

Even all the way out, it did not appear to be quite touching the diaphragm.

That's almost enough information.
I presume 1) that the valve did not leak at your 1st stage IP in this configuration
and 2) that you are telling me the lever height was "just below" the diaphragm. The adjustment knob position won't affect lever height, only the orifice position.

Therefore, this is a good position for the lever if the valve is sealed and the orifice is about 1/12 turn past sealed. If the orifice is screwed in a lot more to get this tiny gap between diaphragm and lever, that's not a good thing.
So if the orifice was just past sealed, and with the adjustment knob all the way out, what was your cracking effort?

If the orifice was in a lot more, then how high does the lever get when the orifice is 1/12 turn past sealing?

Maybe I'm asking too many interrelated questions. PM me if you like.

Rob

 

[Rusty Shackleford]

All the way out meaning the maximum liver height the matter what I did I couldn't get the lever to quite completely touch the diaphragm.

For now, I just adjusted it to where it was as hot as it could be, and I left it there and then finished the adjustment with the balance chamber.

 

[Couv]

Maybe I'm asking too many interrelated questions. PM me if you like.

Rob and Rusty,

This a very informative thread with information that this forum was created for. Taking it underground (unless you have business matters to discuss) would be a sin and a shame.

 

[rsingler]

I just adjusted it to where it was as hot [high?] as it could be, and I left it there and then finished the adjustment with the balance chamber.

I'm dying to hear...
did you get the cracking effort down to an acceptable level?

(Roger, couv! We won't sneak away together. I promise. )

 

[Rusty Shackleford]

Bad news and good news. Bad news is the high-pressure O ring on the MK 20 blew about 30 seconds after I pressurized the regulator today.

Good news is I had a great dive in Summersville lake today. This is why you always bring a spare set of regulators with you I am assuming it was the high-pressure O-ring that blew because I haven't taken apart yet. It made a high pitched leak in whistle noise and submerging it the bubbles came out of the pressure equalization ports on the first stage. I did not rebuild the stage myself a famous dive shop in central North Carolina rebuilt it whom shall remain nameless because everyone can have a bad day.

So I did not get the test today as I had planned perhaps next week. Will take the first aid your part tonight and analyze the failure. I am likely going to need a high pressure O-ring to replace the one that I cannibalize out of a rebuild kit. It should be only that part that needs to be replaced. Can anyone hear recommend a source for that par? If McMaster-Carr ha a part number I'll buy a bag of them.

 

[Rusty Shackleford]

What is funny is I had this reg on my test cylinder and accidentally left it pressurized overnight. It was when the 500 had a slow leak and the cylinder dropped from 3k to about 600psi before I noticed it the next morning so it had been pressurized before.

That said, The IP was creepy. It stayed in the proper range but it acted strange compared to the regs Inassembled a couple weeks ago and other Regs I recently done.

Could the o ring have been nicked during its service last summer?