Scubapro G250: strange free flow

[Zung]

Dear Board,

I have a strange behavior in a SP G250: when I turn the air on, initially, everything is fine. But after a few breaths, it starts freeflowing slightly, a small hiss. I turn the adjustment knob in maybe half a turn, it stops. After a few more breaths, it free flows again, somewhat less than before, but still noticeable. And this goes on.

First I think maybe the poppet has a problem, replace the whole assembly: poppet+ seat + balance chamber + spring. Same thing. Then I replace the orifice. Still the same.

I don't have anymore part to throw at it. What can it be?

 

[redacted]

Is IP good?

Have you determined whether the leak is from the seat of the balance chamber?

Tough one.

 

[halocline]

First, make sure that the IP isn't creeping with whatever 1st stage you're using. Once that's okay, considering you've tried everything else, the only thing I can think of is maybe the poppet is sticking in the barrel. Try filing a little bit off the wings of the poppet (just a little) and while you're at it very thoroughly clean the inside of the air barrel.

You might also check to make sure the lever feet are working freely on the poppet tabs, but I suspect that's not the problem.

The few times something similar has happened to me it was the spring or that crappy plastic orifice.

 

[Zung]

IP is rock solid at 9 bar / 130 PSI.
Sorry forgot to tell you I put everything in the ultrasonic before attempting to swap parts.
What I haven't done is to look at the thing with the cover off; will try tomorrow.

Edit:
The 1st poppet/chamber/spring/seat/o-ring were new, and so is the 2nd assembly, straight out of the box.

 

[herman]

For what it's worth, I picked up one a while back and it also "freeflowed". Turned out the plastic balance chamber had split along it's mold line. Yours might be slightly cracked and flexing enough to come and go.

 

[Zung]

I replaced the lever with a NOS stepped lever for the 109.
It still free flows.

Replaced the diaphragm.
It still free flows.

Now if I leave the cover off, the free flow stops.

 

[halocline]

You should try the newest style lever, it has curved feet. Or, take the lever that was in your G250 originally, and clean up the feet area with a small file, looking for anywhere it might bind slightly. Inspect the square holes in the air barrel and if you have a small enough file, clean up the corners.

If it doesn't flow with the cover off, but does with it one, it means the lever is too high. It sounds like the lever is not returning to the exact same position after breathing. The action of the lever feet against the air barrel and/or poppet tabs is an area that SP could improve on. Ideally you'd want a very stable but friction-free anchor point in the air barrel and a very consistent, free cam action with the poppet tabs.

 

[redacted]

I replaced the lever with a NOS stepped lever for the 109.
It still free flows.

Replaced the diaphragm.
It still free flows.

Now if I leave the cover off, the free flow stops.

This may get to be fun!!! That suggests the lever is too high. That is consistent with the symptom of screwing in the user adjustment does not cure the FF. If you can cure it with a lever swap the great. I have successfully bent a lever slightly with good results but that is a chancy course. Another cure is to screw the orifice (not poppet) in a bit more to bring down the lever height and get a good seal. That will probably raise cracking pressure above spec. I suspect the cure for that may be to shorten something on the other end. I would be very hesitant to take material off the adjustment knob and the balance chamber does not seem to have much material on the sealed end to work with. I guess that leaves the poppet or the spring. If you can find a slightly shorter or weaker spring, that should work with no risk of damage. Otherwise, a little adjustment of the poppet where it engages the end of the spring should do the trick with nothing but a plastic poppet put at risk.

Enjoy.

Edit: One way to play with this idea a bit is to remove the clip on the adjustment knob so you can set that knob a bit beyond the stop and see if that cures the problem. You might even be able to bend the clip a bit if that works to allow the knob to stay there.

 

[Zung]

Thanks Gents, I'm beginning to see The Light.

I still have one last part swap before I start with the irreversible matter removal: the original single o-ring (balanced) poppet. And maybe a plastic orifice in place of the current metal. After that, EVERYTHING will have been replaced: this one is the toughest 2nd ever!

But 1st thing 1st, it's dinner time.
I'll report back later.

 

[halocline]

You mean you have not been using the current s-wing poppet?