Whine in a Mk10

[rsingler]

You may have run across that really irritating whine in your Mk25, and Scubapro has long fought that issue with a variety of trial fixes.
But until today, I had NEVER run across it in a Mk10. Just finished a standard overhaul and used an OEM Service kit 10.500.045, two shims and a -| seat for the repair. Locked up right at 135 with no creep, and I was happy until I breathed from the second stage.
A loud, high-pitched whine sung out, and I thought, WTH? There's no stack spring in the HP gas pathway to vibrate! So I did the other Mk25 fixes: I greased up the the o-ring and piston shaft with extra lube. I rotated the HP Seat 180°. Nothing helped. At 500 psi, the whine was almost gone, but at full tank it was unbearable.

To digress, in the old days, that purple .147 o-ring would rarely buckle and your HP seat carrier would bubble away.

The same problem exists with the 2-013 that folks use when they make up aftermarket kits. It's not common, but it happens.
Well, Scubapro made a switch somewhere around '98-'99 to that orange plastic washer, and they've stuck with it.

Well, here's what I think was happening today. I think the square edge of that washer, for some reason in that high-flow gas pathway, was acting like the mouthpiece of a flute. Because of the problem of that thinner o-ring in the old days, I'd been using a metric 10x2mm duro 90 oring in my aftermarket kits. So I stuck one in this reg, even though I was a little unhappy about deviating from an OEM kit for a customer.

And when I switched that 10x2 in, in place of the plastic washer, things were completely quiet. I think the rounded surface smoothed out the flow.

I'm learning new stuff every year. I thought I had the Mk10 down pat after all this time...

 

[Pressurehead]

It's fixes like this I like this site. Thanks Rob.

 

[Mobulai]

And here I thought xmas gifts come a bit later, awesome discovery/soln.

Next time I rebuild an mk10 I’ll try to remember filing/rounding off the square washer if O haven’t sourced any 10x2s, just in case

 

[happy-diver]

Fairdinkum, half a dozen years ago half a dozen regs, two sets for manifolded tanks and a couple
of stage bottles, and they are screaming and I'm using orings as that is all I know, and the people
on the boat are fixing them for me, put extra grease on the piston put new seats different grease

Went home swapped all the seats around some old some new and voila life was wonderful again

Took them back into the water recently untouched and could not even hear the piston operating

But boy was the exhaust pumping, through only one port really loud, maybe that was the reason

With nice clean cam bands holding the vessel to the pestle

Did you all know that when you add a pound of weight to your cam band
you are adding a pound of weight, to the 35 pounds, that is already there

Did you ever hear anything like that

Yeah interesting!

 

[halocline]

You may have run across that really irritating whine in your Mk25, and Scubapro has long fought that issue with a variety of trial fixes.
But until today, I had NEVER run across it in a Mk10. Just finished a standard overhaul and used an OEM Service kit 10.500.045, two shims and a -| seat for the repair. Locked up right at 135 with no creep, and I was happy until I breathed from the second stage.
A loud, high-pitched whine sung out, and I thought, WTH? There's no stack spring in the HP gas pathway to vibrate! So I did the other Mk25 fixes: I greased up the the o-ring and piston shaft with extra lube. I rotated the HP Seat 180°. Nothing helped. At 500 psi, the whine was almost gone, but at full tank it was unbearable.

To digress, in the old days, that purple .147 o-ring would rarely buckle and your HP seat carrier would bubble away.
View attachment 875977
The same problem exists with the 2-013 that folks use when they make up aftermarket kits. It's not common, but it happens.
Well, Scubapro made a switch somewhere around '98-'99 to that orange plastic washer, and they've stuck with it.
View attachment 875979

Well, here's what I think was happening today. I think the square edge of that washer, for some reason in that high-flow gas pathway, was acting like the mouthpiece of a flute. Because of the problem of that thinner o-ring in the old days, I'd been using a metric 10x2mm duro 90 oring in my aftermarket kits. So I stuck one in this reg, even though I was a little unhappy about deviating from an OEM kit for a customer.
View attachment 875978
And when I switched that 10x2 in, in place of the plastic washer, things were completely quiet. I think the rounded surface smoothed out the flow.

I'm learning new stuff every year. I thought I had the Mk10 down pat after all this time...

Rob, I have a feeling that switching out the HP seat seal for an o-ring might have been a red herring. I just don’t see what could be vibrating in that spot. The typical whining is caused by the piston and/or main spring vibrating. I was going to suggest either replacing the main spring or simply turning it around. But, since I don’t have an alternative explanation of why it stopped making noise (and presumably you didn’t touch the ambient chamber parts when you replaced the seal) then congratulations, you’ve fixed another touch one!

 

[rsingler]

Yes, I had never seen it before. I'm sure that my reassemblies rotated the mainspring (I don't know if I removed it from the piston, so I may have flipped it over, too). Alas, it's gone back to the customer, so I can't play with it further.
Have you seen that in a Mk10? It was a first for me. With no gas flow in the ambient chamber, I had never considered main spring vibration. All my Mk25 and Atomic success with whine has been playing with the little spring that holds down the stack of washers and HP o-ring, as it sits directly in the high speed flow path for tank gas.

Happy New Year, Matt!

 

[halocline]

Yes, I had never seen it before. I'm sure that my reassemblies rotated the mainspring (I don't know if I removed it from the piston, so I may have flipped it over, too). Alas, it's gone back to the customer, so I can't play with it further.
Have you seen that in a Mk10? It was a first for me. With no gas flow in the ambient chamber, I had never considered main spring vibration. All my Mk25 and Atomic success with whine has been playing with the little spring that holds down the stack of washers and HP o-ring, as it sits directly in the high speed flow path for tank gas.

Happy New Year, Matt!

It used to happen on MK5s for me and occasionally on my MK2, so I know it had nothing to do with the little spring that holds the HP bushings in place on the MK25. I think your flute analogy is apt, but I believe it’s the piston edge that acts as the vibrating ‘reed.’ That’s where the air is moving the fastest. Then the piston vibrating starts resonating with the main spring. I believe the whole thing is kind of hit-or-miss in terms of resonance and that’s why it happens at some tank pressures, and why adding a shim or otherwise adjusting IP or even just turning the spring over can interrupt the noise.

 

[rsingler]

Well, @halocline , you're absolutely right: red herring.
Had two old Mk10's in the shop last week and  both whined at 3000 psi, but only one had a tiny squeak at 1500.
Traded the orange washer for 10x2 - no change
Rotated the main spring 1/2 turn. Changed seats and added shims. I started by trying to keep track of each step I took. But nothing worked. It was so frustrating by the end that I can't honestly say what did it for both regs.

It was clear that getting the IP I wanted was part of the harmonic issue. They both started over spec at 148 & 153.

I  think that flipping the spring over helped. I think that polishing the spring ends helped. And I think that settling for a slightly higher (138) IP than I had planned helped.

But it wasn't my magical o-ring.
Thanks for the skepticism, Matt. How it is I've never seen it before and now three in a row is telling me something. Maybe it's the switch from thick silicone in the old days to slippery T-71.

 

[Pressurehead]

But it wasn't my magical o-ring.

I was hoping this was the easy fix.

 

[bretski]

So glad I could be your guinea pig, @rsingler !