Help! Another Scubapro MK25 whistling

[rsingler]

Halo's comments are right on the mark. And congrats to you for taking the equipment course. Sounds like you indeed are proceeding in a methodical fashion. I apologize.
Sorry I was unclear about rotating the seat, but your returning it to its original orientation more likely than not also included a different "clock position" which may have solved the issue.
Sounds like it's ready to throw on a pony and take for a test.
Best of luck. It's gotta be tough being isolated, though I imagine many of us would love to trade with you.

Rob

 

[NozBzh]

What could you possibly have learned about how your Mk25 works, troubleshooting, and repair that made you think you should rebuild it with new parts "several times" and flip the seat over??? That is alarming.

I meant I rebuilt it with a new service kit, it still whistled so I took it apart and rebuilt it again with the same (new) parts. That doesn't seem too unreasonable to me. I have a whistling sound due to an unknown cause, no apparent leak, so I restart from the beginning. Apparently that seems crazy to you.

As for the flipping the HP seat over, it seemed weird to me but rslinger's suggestion was unclear, at least to me. It's the "180 degrees" that confused me. Yes it seemed weird and I still did it, because if it didn't work, it was less irreversible than cutting the bushings as was also suggested.

---------- Post added December 6th, 2013 at 09:08 AM ----------

You can't flip that seat over. One side is machined (or molded) to precisely fit the piston edge, the other side is not. Trying to pressurize the reg with the seat upside down wouldn't be much different than just connecting a 2nd stage directly to the tank....not so good.

I don't work on these too often, I don't own one, but the seat I'm looking at now has a small dimple on the side that fits in the seat retainer. But you shouldn't confuse this with any sort of recess to fit the piston; the two sides don't look at all similar, it't not like a flat puck seat that you can flip over to use the other side.

Rsingler was suggesting that rotating the seat, meaning turning it like a volume control knob while it's in the seat retainer, might subtly change the resonance between the piston and seat, quieting the whistle. Again, it's not really a 'whistle' its more like a harmonica. I don't know how much you understand about the causes of the harmonica sound (bet you're learning a lot!) but it's because air moves very fast over the piston edge when it opens up, and this creates vibrations. This is similar to how woodwind instruments like flutes work, and when conditions are right, there's enough vibration and resonance to cause the 'musical' sound. It's not a leak at all. If you have any sort of leak, your problem is different. A leak and the harmonica sound? That means two different (but maybe related) problems.

All the tricks like re-lubing the o-ring, moving the seat, bending the small spring (that's a good one, rsingler, BTW, and so is the check to make sure the main spring is not 'balanced') etc...are to disrupt the resonance that occurs with this quick air movement through the piston. It's not just a MK25 problem, all piston regs are susceptible to it. My MK2 sang like a nightingale after a rebuild once.

Anyhow, best of luck and hopefully the problem is solved.

Yes I know one side is molded to fit the metal spacer and the other to fit the piston. This is why I said something didn't look right to me when I flipped it over, which them made very cautious when I turned the air on. Sure enough, it made a big leak. I know which side goes where but as I said in the previous post, it's "180 degrees" that confused me, and since I tried many times to sort out this whistling, I just thought no harm in trying. I always press the purge on my second stage when I turn the air on after I touch my first stage, and I was very cautious turning the air on (like you would do for 100% oxygen tanks).

I am indeed learning a lot, thanks a lot for the help.