Scubapro chrome plated brass regulators...

[saxman242]

Have you tried changing hoses? I wonder if you'd find the same fluctuations with a longer or shorter lp hose

 

[Open Ocean Diver]

With no leaks underwater, your piston shaft HP seal is good, and your piston ring (LP) is good.

With a steady IP, your HP seat and the knife edge is good.

So to me, the first stage is fine.

Next thing I'd try is to change the amounts of suction pump rpm and air bleed, and see if that eliminates the resonance. From your video, it sounded like you could try both higher and lower rpms on the pump. I don't know if you have similar latitude in your flowmeter.

Three different flow rates, varying bleed and rpm. can’t get it to oscillate now. Weird

 

[rsingler]

Well, that's great news!
I suspect you happened upon some magical resonant alternation of second stage valve opening and closing just by luck (good or bad).
Looks like a good performer, in both stages!
Congratulations on your persistence.

 

[Open Ocean Diver]

Well, that's great news!
I suspect you happened upon some magical resonant alternation of second stage valve opening and closing just by luck (good or bad).
Looks like a good performer, in both stages!
Congratulations on your persistence.

Thank you, the only thing that’s has me puzzled is it was fairly persistent to the point where I removed the filter put it back on the tank and it was still oscillating, changed tanks and once again oscillating. Almost like it’s an intermittent problem.

 

[Angelo Farina]

Thank you, the only thing that’s has me puzzled is it was fairly persistent to the point where I removed the filter put it back on the tank and it was still oscillating, changed tanks and once again oscillating. Almost like it’s an intermittent problem.

It could be that there is a very particular regimen of air flow which makes the opening of the valve (piston) to become unstable. I did find a similar case with an hydraulic steering unit, at a particular speed of rotation of the steering wheel the system was unstable and the wheels were rotating erratically.

 

[Open Ocean Diver]

It could be that there is a very particular regimen of air flow which makes the opening of the valve (piston) to become unstable. I did find a similar case with an hydraulic steering unit, at a particular speed of rotation of the steering wheel the system was unstable and the wheels were rotating erratically.

Funny you mention... my mom back in high school gave me 1967 Chevy Impala. I Remember the exact same thing with the steering.

I’ve tried everything won’t duplicate. Tomorrow I’ll fill my tanks maybe it’s HP pressure related.

 

[GJC]

I notice that you are using a different Magnehelic than the one that showed oscillation. Might there have been some unique harmonic oscillation with the other Magnehelic and the configuration and length of hoses and tubes?

 

[Open Ocean Diver]

I notice that you are using a different Magnehelic than the one that showed oscillation. Might there have been some unique harmonic oscillation with the other Magnehelic and the configuration and length of hoses and tubes?

Same one, I use 5-0-5 on the flow tester, 0-3 on the pump. oscillations were measured on the 0-3 mag. That I’m not sure, used the same hose with different 2nd’s never thought to use a different hose.

 

[Open Ocean Diver]

Same one, I use 5-0-5 on the flow tester, 0-3 on the pump. oscillations were measured on the 0-3 mag. That I’m not sure, used the same hose with different 2nd’s never thought to use a different hose.

 

[rsingler]

Okay. I've watched this video
https://share.icloud.com/photos/0F5bO9lhXbQxWvNtN_BsopviA#Downtown_Toronto
a dozen times, now. Here is what I think is going on...

The micro pump is sucking at a very small rate from the mouthpiece of the second stage (remember that much of the pump performance is deliberately wasted by the bleed from the flowmeter, to keep changes small and slow).
As the pump sucks, the magnehelic drops from zero toward the cracking effort negative pressure (even though it's registering as a positive displacement of the Mag needle).
When the negative pressure reaches cracking effort, the second stage valve begins to open microscopically. But what we noticed here was an increasing number on the magnehelic despite a dropping IP. Whaaat?

I think that is occurring because, at this very early point in valve opening, the micro pump was able to keep up with the output from the second stage. During this brief interval then, the IP continued to fall as flow increased from the second stage valve. And the magnehelic continued to rise because the micro pump could keep up with the tiny second stage flow to develop more negative pressure, opening the valve further.

At some point, however, the flow from the second stage valve overcame the ability of the micro pump to suck, and the negative pressure at the mouthpiece dropped back to zero. When that happened, the valve closed in the second stage, the valve closed in the first stage, and the IP returned to baseline. With the micropump continuing to run, the process began all over again: magnehelic rises towards cracking effort; IP begins to drop; cracking effort is reached and the micropump keeps up with the initial flow and continues to suck more negative, until the valve opens fully and the micropump is overcome. And it starts again...

But it was a magical combination of rate of suck and rate of valve opening that allowed this to appear. "Could not duplicate" has been uttered by more than one garage manager when presented with a bizarre auto problem. Same thing here, I'm guessing.