MK25/G260 whistling

[redacted]

The insertion tool we use in the shop is made of plastic or Teflon,.. not sure which. Looks like the metal ones, but is hollow on the wide end (that holds the o-ring/ bushing assembly in the chamber while pushing the piston through. Yes, the course I did 2 yrs ago was only 2 days, but I had serviced 100's of those regs in the years before I went. My mentor who originally taught me was VERY mechanically inclined (I'm not particularly, but I did learn to do it & do it well). Though the course was short, I did manage to learn a few techniques that made life easier & made things more efficient. The course was taught by the designing engineer of the regulator. No offense taken.

It sounds like your instructor taught you a different method than is called for by Scubapro in EB 267. The recommended method is the use the tool to insert the first bushing without the o-ring and 2nd bushing. You then flip the tool to hold that bushing in place as you insert the piston and install the ambient chamber. Then you remove the tool and install the o-ring and 2nd bushing over the end of the piston again using the tool the push them into place. It sounds to me like your instructor had you install both bushing and the o-ring before inserting the piston. I have done this but you have to have a very light touch holding that sandwich in place to keep the o-ring from dislodging and blocking the installation of the piston. If it is dislodged and you push hard enough, you could damage the o-ring even with that dull edge. In that case, using the tapered bullet tool should help push the o-ring out of the way and back in place. It works, it is just not the Scubapro documented procedure.

BTW, my metal tool also has plenty of room for the bullet tool to be used as you describe. There is more than one way to skin a cat.

It really is good to read the manuals. Every time I do I find something I had forgotten or overlooked.

 

[buddhasummer]

Went out for a dive this morning before work and to my surprise the whistling has stopped. Go figure. I wonder if it was a one off or will return. Time will tell I guess.

 

[redacted]

Went out for a dive this morning before work and to my surprise the whistling has stopped. Go figure. I wonder if it was a one off or will return. Time will tell I guess.

It may be that some lube just had to move around a bit to stop the friction. Scubapro usually loads up the lube on those dynamic o-rings. The whistling is really much more annoying than any danger. I would just dive it as is rather than go through the nut roll of trying to have it fixed; with the reasonable hope that it works OK until the next service.

 

[buddhasummer]

I have the tools on order, an accessible supply of service kits so when the time comes guess I'll pull it apart. I've no trouble servicing Apeks so guess these won't be a quantum leap. Hopefully you are right and lube has got where it needed to be. Cheers.

 

[buddhasummer]

It came back, sporadically, but definitely back. I tried to tune out but the more I tried the more it irritated me, don't think of pink elephants and all that. Tools on the way, thanks Herman, I'm OCD so will pull it apart and silence it. Cheers.

 

[fmerkel]

Old thread but among the ones I found searching for [Scubapro MK20 whistling] this one seems the most useful. This is an overhaul when the 1st stage was found to be leaking out of the ambient chamber at a slow trickle. Reg was working fine. I found the piston O-ring somewhat shredded and with the help of this forum learned I was putting one of the bushings in upside down. GREAT!. Re-assembled using all previous parts (1 year use, looked fine), with a new kit O-ring for the piston.
No leaks, IP stable @ 130, breathes nice. Took it for a dive, persistent whistle from 3500>600. Even the BC inflator squeaked.

This thread indicates more lube, maybe flip the spring. Did that > still whistled. Even more lube, thick silicone on the spring ends, moved a shim > still whistled. One more time > still whistled. Rats!

Thought maybe the bushing being in wrong which allowed the O-ring to get shredded maybe caused unusual movement and wear in the bushings. Put in new bushings > Whistling gone!
By eye and feel I could not tell the difference in the old vs new bushings.

 

[halocline]

The whistling is caused by vibrations in the piston resonating, my guess is with the spring. When the 1st stage valve opens under demand, HP air rushes past the piston edge, and starts the piston vibrating. It's kind of like a flute mouthpiece, there is no way to prevent the piston shaft from vibrating. So the only thing you can do is dampen the vibrations enough so that they don't resonate and cause sound. This is basically hit-or-miss, although I will say that I've never had a MK5 or 10 whistle after servicing it. My MK2 used to honk from time to time.

 

[fmerkel]

The whistling is caused by vibrations in the piston resonating, my guess is with the spring.

First time I've had this issue in 10 years of overhauls. I flipped the spring, moved shims, coated with Dow thick silicone.....none of that worked. Only replacing the bushings did any good. Have not dived it yet so don't know if it'll stay quiet through the whole tank pressure cycle.

 

[halocline]

I guess in your case the bushings really changed the way the piston can or can't vibrate, but don't forget that changing the bushings also means that you remove everything else and replace it, so it's hard to know exactly what fixes it. Personally I think it's hit-or-miss with the whistling issue as to what exactly is allowing the piston to transmit enough vibrations to make a sound.

I do know that it never happens on my MK5s or MK10s, but they have a knife edge piston, which is not nearly as aerodynamic as the round piston edge in the MK25. That is, in fact, why they changed to that style of piston; air gets around that round piston edge very efficiently. So I guess it's better at setting off harmonic vibrations in the piston.

 

[fmerkel]

Do you think re-working the edge of the piston (essentially making it flatter with very fine sandpaper) due to IP creep contributes to....or maybe interferes with this kind of harmonic?