MK10 squeals like a pig

[SeaCobra]

The problem is in the piston, yours is cattywampus and not traveling cleanly through the body of the first stage. This causes the squeal/whistle and can affect ip lockup.

 

[DA Aquamaster]

As noted above, a rough (inconsistently rough) or mis-aligned piston will resonate regardless of the quantity or quality of lube used. in some cases if the roughness is in an isolated spot, changing the Ip/seat height significantly can help if the HP o-ring then rides in a slightly different spot. But basically the fix is to replace the piston.

 

[halocline]

It looks like I flattened the knife edge of the piston too much which messed up the balancing of the reg. Now a 1000psi difference in tank pressure will change IP by about 8psi. Over the full range of tank pressure it will probably be close to 20psi.

I'm not sure how this would cause more IP rise with increased supply pressure unless the piston is sealing on the 'inner' edge and leaving a small 'shelf' exposed to supply pressure. But, one I've noticed is that IP rise in my MK10s is not really linear with an increase in supply pressure. I think actually more of the IP rise has to do with increased friction and very slight extrusion in the HP o-ring. When I switched to a 90 duro polyurethane o-ring there was noticeably less IP rise with supply pressure increase, and of course the geometry of the piston was unchanged. Anyhow, due to the factoring in of friction and extrusion, I found that there's basically a 'bump' in IP going from around 1000 to 2000 PSI,(That could easily vary from reg to reg) in which most of the IP rise occurs. So that might explain your 8 PSI rise, at least partially.

Bottom line, if the reg is locking up well and working well, I wouldn't be in a huge hurry to replace the piston. They seem to be going for around $40 on ebay these days; not a lot, but also not much less than MK10s used to go for.....then again, it's nice to have a spare piston or two.

 

[bkbomb123]

I had the same problem with the flat white seats. The 1st stage would sound off at 70' and stop at 10'. When I changed to the grey conical seat all noise stopped.

 

[Six2Life]

Problem solved.

I swapped out the piston from a donor MK10. This fixed the creep but the noise was still there. So I swapped out the last part I could think of that could possibly be causing the noise, the stem oring. A viton 90 eliminated the problem completely. I really didn't suspect the poly oring since it came out of the same bag as the oring in the quiet MK10. Production tolerances I guess.

 

[DA Aquamaster]

The older tan colored urethane looking o-rings had a 5 year shelf life and have been out of production for at least 15 years.

An issue with the Mk 10 is the wear in the reg body, as the brass body is softer than the piston. Over time this results in larger clearance between the piston and body, which at high pressures can result in the piston stem o-ring getting pinched. This pinching will result in cresent shaped pieces being cut from the o-ring, but in the short term, the greater resistance to the piston's movement can cause vibration and resonance.

The use of 90 duro o-rings was I think intended in part to help prevent this problem in older Mk 10s and in Mk 10s being used more frequently at high (3300 psi) pressures.

 

[Six2Life]

All orings used in these regs were new sourced from oringsusa.com. Both of the poly -10's for the stems were also duro 90. I used the poly's for their supposed extrusion resistance to try to keep IP stable across all tank pressures. I'll have to see if switching to viton made any difference. FWIW I don't think the material had anything to do with the noise. That particular poly oring just happened to be on the tight side. The piston slid into place much easier with the viton.

 

[redacted]

All orings used in these regs were new sourced from oringsusa.com. Both of the poly -10's for the stems were also duro 90. I used the poly's for their supposed extrusion resistance to try to keep IP stable across all tank pressures. I'll have to see if switching to viton made any difference. FWIW I don't think the material had anything to do with the noise. That particular poly oring just happened to be on the tight side. The piston slid into place much easier with the viton.

I would expect that the effect of 3000+ psi would overwhelm any differences within tolerances of the two o-rings. Are you sure the fix was not simply a result of the re-lubing. I know when I get one that starts to squeal, a little added lube will often fix it.

 

[halocline]

I suspect the squealing can be caused and/or cured by any number of little nit-picky factors; lubrication, o-ring composition, maybe even the glaze on the piston shaft, maybe something to do with the spring, anything that could fail to dampen the vibrations caused by the air rushing past the piston edge. If you think about it, that type of air movement is sort of like a flute; air rushes past a thin metal surface and starts vibrating a metal tube.

So, certainly the o-ring and lube wrapped around the piston shaft could be responsible for most of the dampening.

 

[Six2Life]

I think the only way I could have put more lube on those orings would have been to just pack the ambient chambers.

I do remember the suspect oring being uncommonly tight when inserting the piston. It was tight enough that I had to hold the bullet onto the piston from the HP side otherwise as the piston/bullet junction passed through the oring it would separate the two.