Scubapro balanced adjustable second stage freeflowing

[Still Kicking]

Whenever I have had trouble getting an SP second stage to behave it usually comes down to the spring. Sometimes they develop a micro crack that reduces the spring force ... if you pull the spring a little it might break. Replace the spring and I bet all will be well

 

[MarkH]

If my notes are correct, your spring should measure 23.00 mm in the relaxed state, with a constant k of about 2300 N/m. I’d be very interested to hear what your measurements show.

That's an awesome tool and method for calculating the spring force! I'm not a drug dealer anymore so I don't have a small scale, but I tried using a digital bathroom scale and a vernier caliper. The uncompressed spring length was 23mm just like yours. I'll attach a picture of my results using your converter. The average seems a bit lower than yours, but I don't know how accurate the bathroom scale is at such low values. I assume that if the spring is the right length and there is no visible damage or corrosion, then it should be fine. At least in the automotive world, the shop manuals for my old cars just say to measure spring length (for valve springs for example) and if the length is within spec then they are still good.

 

[wdeutsch]

That's an awesome tool and method for calculating the spring force! I'm not a drug dealer anymore so I don't have a small scale, but I tried using a digital bathroom scale and a vernier caliper. The uncompressed spring length was 23mm just like yours. I'll attach a picture of my results using your converter. The average seems a bit lower than yours, but I don't know how accurate the bathroom scale is at such low values. I assume that if the spring is the right length and there is no visible damage or corrosion, then it should be fine. At least in the automotive world, the shop manuals for my old cars just say to measure spring length (for valve springs for example) and if the length is within spec then they are still good.



View attachment 916006

If you want to test the spring theory without buying a new spring, can you shim it a bit? Given Hooke's law, if you compress the spring a bit with a little flat disc of something, then the force exterted in the "extended" position goes up. If that solves your problem, you know the spring was the issue. If not.... Well, it was a cheap thing to try.

I'm not familiar with the reg in question, so I don't know how feasible a small platform shim would be, but maybe you can figure something out?

 

[MarkH]

If you want to test the spring theory without buying a new spring, can you shim it a bit? Given Hooke's law, if you compress the spring a bit with a little flat disc of something, then the force exterted in the "extended" position goes up. If that solves your problem, you know the spring was the issue. If not.... Well, it was a cheap thing to try.

I'm not familiar with the reg in question, so I don't know how feasible a small platform shim would be, but maybe you can figure something out?

This reg has an adjustable second stage with a knob that you turn in to compress the spring. Turning in the knob is like adding shims. When the knob is screwed all the way in, it's like adding almost 1/2" of shims.

 

[Still Kicking]

If you want to test the spring theory without buying a new spring, can you shim it a bit? Given Hooke's law, if you compress the spring a bit with a little flat disc of something, then the force exterted in the "extended" position goes up. If that solves your problem, you know the spring was the issue. If not.... Well, it was a cheap thing to try.

I'm not familiar with the reg in question, so I don't know how feasible a small platform shim would be, but maybe you can figure something out?

Possible indeed. The G250HP uses a shim between the spring and the balance chamber. In a nifty piece of repurposing, it's a MK20/25 first stage bushing (010.60.607).

 

[Tanks A Lot]

[...]The uncompressed spring length was 23mm just like yours. I'll attach a picture of my results using your converter. The average seems a bit lower than yours, but I don't know how accurate the bathroom scale is at such low values. [...]

A great point on the length, as that is what usually changes over time. Assuming the 300 N/m difference comes from the scale, your spring does indeed appear to be perfectly intact. I do like to check the spring constant, just in case the spring was swapped out with an aftermarket one.

One point from your opening post confused me slightly. You wrote:

[...]My problem is that I can't get it to stop freeflowing except when I turn the adjustment knob all the way in. Even then, air hisses by intermittently after I purge it.[...]

Am I understanding this correctly? With the knob fully turned in, you purge the second stage and sometimes it hisses, sometimes it doesn’t? If so, I would strongly suspect that the seat and orifice are not always meeting in the same plane, but occasionally at a slight angle.

Did you have a chance to check the following?

[...]

• Are the short lever feet in good shape, or is one slightly bent? This would put uneven forces onto the poppet, potentially skewing it inside the barrel.
• Does the spring cause uneven pressure? Roll it on a flat surface, does it wobble?
• Are the threads for the orifice in good condition, especially inside the barrel? A crooked orifice in its seating could cause problems, though it’s difficult to verify without cutting the barrel open.

If possible, take a sharp, in-focus photo of the indent in the seat. If the depression is not evenly deep across the seat, this strongly suggests that the seat and orifice are meeting at an angle. In that case, the cause is almost certainly one of the issues listed in the last quote.
Another possibility is that the broach accepting the lever feet inside the barrel has one damaged side.

 

[MarkH]

One point from your opening post confused me slightly. You wrote:

Am I understanding this correctly? With the knob fully turned in, you purge the second stage and sometimes it hisses, sometimes it doesn’t? If so, I would strongly suspect that the seat and orifice are not always meeting in the same plane, but occasionally at a slight angle.

Did you have a chance to check the following?


If possible, take a sharp, in-focus photo of the indent in the seat. If the depression is not evenly deep across the seat, this strongly suggests that the seat and orifice are meeting at an angle. In that case, the cause is almost certainly one of the issues listed in the last quote.
Another possibility is that the broach accepting the lever feet inside the barrel has one damaged side.

With the knob turned all the way in, the flow would often stop, but as soon as I took a breath or hit the purge slightly or touched the lever, it would start hissing again and not just a tiny hiss, but enough for me to call it a freeflow, although not a loud, violent freeflow. As for your other questions:
Lever feet: They seem fine and not bent. I tried the lever from my 109 second stage that works fine in the 109 and it acted the same (freeflow), although I should be able to take the lever out altogether and the reg shouldn't leak so I don't think the lever is causing it. I ordered a couple of the newer curly levers that you're supposed to use with the S wing poppet anyway.
The spring is straight and seems like new when I look at it up close.
It's hard to tell the condition of the threads in the barrel. The orifice screws in ok, but there's the resistance of the o-ring of course. It's not cross-threaded or anything. I ordered one of the new plastic orfices that Scubapro replaced the metal ones with, just to try out a new orifice.
As for the poppet seat, it has now formed a couple of minor indents, which is probably why the out-of-focus picture looked like it had am out-of-round indent. The problem with these regs is that you only get one chance to set it up. If you take it apart and re-assemble it multiple times, the orifice and seat don't match up exactly every time and you end up with a misaligned groove. I'm now leaning toward my issue being a orifice/poppet issue. I got the poppet from E-bay. They claimed it was OEM, but who knows. The length was the same as the old-style poppet. I think next, I'll try and find another S wing poppet or at least a new seat. My problem is finding a seller that doesn't charge $40-60 for shipping (to Canada). The real shipping cost for something that tiny that weighs almost nothing is around $14 (including customs brokerage). To pretend that shipping costs $40 and then pocket the difference is almost the definition of fraud, but all the sellers seem to do it.

 

[Tanks A Lot]

[...]I should be able to take the lever out altogether and the reg shouldn't leak so I don't think the lever is causing it.[...]

While this is from a G250, the principal remains exactly the same.

As you noted that the feet are in good shape, could there be something on the barrel broach that catches the lever earlier on one side only? That might cause an occasional crooked poppet, which could explain the issue. Are the poppet feet in sound shape and equal in length?

[...]The problem with these regs is that you only get one chance to set it up. If you take it apart and re-assemble it multiple times, the orifice and seat don't match up exactly every time and you end up with a misaligned groove.[...]

While that is true, it wouldn’t cause the problems you’re seeing. As you noted, it would produce a slight hiss, not a near free-flow. Is the seat itself in good condition? I once had one with a cut in it, which drove me mad and behaved much like what you describe, though without requiring excessive spring tension from the knob.

It’s an interesting problem for sure. Apologies for chasing ghosts so far. Keep us updated on how things progress.

 

[Nemrod]

I ordered one of the new plastic orfices that Scubapro replaced the metal ones with, just to try out a new orifice.

You will need to change the poppet seat as well. No short cut here. New orifice, new seat.

I like the new plastic orifice. It cannot be tuned as finely maybe but it also is resistant to indenting the seat and can thus go longer intervals for service. All in all I think them an improvement unless you have the Holy Grail of Scubapro orifices, the gold plated versions. And only because they are pretty.

There is nothing wrong with the 109 mechanism. It is tried and true and copied copiously by other manufacturers. It is virtually identical with the current G260 and the currently produced Halcyon (G250V) products. And can use the same parts. The failing of the 109 is the restrictive exhaust and the lack of a Venturi control and this was partially addressed with the 156 CE. The other issue for me is maintenance of all that chrome plating which is no different than an AL/USD 1085 or the modern Scubapro A700.

 

[Mobulai]

E-bay. They claimed it was OEM, but who knows. The length was the same as the old-style poppet. I think next, I'll try and find another S wing poppet or at least a new seat. My problem is finding a seller that doesn't charge $40-60 for shipping (to Canada). The real shipping cost for something that tiny that weighs almost nothing is around $14 (including customs brokerage). To pretend that shipping costs $40 and then pocket the difference is almost the definition of fraud, but all the sellers seem to do it.

That’s an ebay thing (in my experience) — I was able to reach out to a couple sellers outside ebay and things were much more reasonable
(Ebay even double charged me when getting tiny stuff from the same person)

Ok, back on topic. One more shot in the dark (even tho unlikely as you said the lever when touched prompted freeflow)
Is there any play in the lever motion (rotationally, basically in the direction it should move in) or “abrupt” clicking when you breathe from the reg?

I just wanna make sure the poppet leg isn’t stuck between the lever feet and the orifice
This happened to me on the 1st g250v I got used and only noticed it in water (when pressing the purge did nothing)