MK10 Question - DA and Others

[mahjong]

I now dive regularly (average 12-15 dives/month) using an MK10 (with the metal-head Yoke nut; I use a balanced adjustable metal second stage). On a whim before a dive, I asked a technician (we meet and hang out in an old dive shop, which is by the boat pier) to check the IP on my MK10. It registered a bit over 150 and was still slowly creeping as we read the gauge. I have many regs (though I almost exclusively dive this MK10 here in HK) and so I cannot recall the exact date of the last service, but I am quite certain that it was within the last year.

My question, in short, is how can I instruct the technician to service or even upgrade (which seat, which piston) my MK10 to minimize the possibility of IP creep?

Also, to what pressure would the IP need to creep before I should become very concerned?

Many thanks.

Mahjong

 

[redacted]

I usually deal with Mk5/10 IP creep problems when it gets to 10+ psi. I set IP about 130 and service before it breaks 145. 150 is a definite service for me. I don't really have any problems with those Mk5/10 seats but so you may want to take a close look at the piston knife edge to see if that may be contributing to the problem.

 

[Couv]

Hello Majong,

First off, I would not dive with that regulator until the IP creep is sorted out. The normal rage is 135 +/- 10psi with no creep. I am more concerned about the creep than the high IP. High IP can be caused and rectified in a few ways, but the creep must be solved first. It could be something as simple is a new HP seat; which is the first and easiest thing to change. Next, if the piston stem o-ring has extruded and is pinching the piston stem, that would be my next fix attempt. But in order to replace the piston stem o-ring, you have to remove the piston; so with the help of a bright light and a 10x magnifying glass, have a good look at the knife edge. Run your fingernail around the edge and feel for any nicks. Check the stem itself for corrosion that could be dragging on the HP o-ring. If there is any, remove the corrosion with a Scotch Bright pad or very fine sand paper or crocus cloth. Generously lube the HP o-ring and stem.

Keep us updated,

c

...quick draw awap...

 

[mahjong]

Thanks AWAP and Couv--both quick draws...I will keep you posted.

 

[DA Aquamaster]

What Couv said...there should be zero creep with a Mk 10 when initially serviced. If it is quickly developing IP creep in service it is most likely a piston problem as any nick in the knife edge will eventually be rotated somewhere else on the seat as the piston rotates slightly and itwill often leak in the old location. Alternatively if the stem is slightly off center, you will end up with two seating grooves over time and they will leak at the two points where they intersect.

 

[mahjong]

Thanks DA. Can the MK10 be upgraded with an MK20/25 piston, or are they all the same today?

What Couv said...there should be zero creep with a Mk 10 when initially serviced. If it is quickly developing IP creep in service it is most likely a piston problem as any nick in the knife edge will eventually be rotated somewhere else on the seat as the piston rotates slightly and itwill often leak in the old location. Alternatively if the stem is slightly off center, you will end up with two seating grooves over time and they will leak at the two points where they intersect.

 

[DA Aquamaster]

The Mk 10 uses a smaller diameter piston than the Mk 5, Mk 15, Mk 20 and Mk 25. It came in a rounded tipped version in the Mk 10 plus that uses a Mk 20/25 style seat and the Mk 10 can be updated to a Mk 10 Plus, but the regular Mk 10 piston and seat usually lock up better.

 

[mahjong]

What Couv said...there should be zero creep with a Mk 10 when initially serviced. If it is quickly developing IP creep in service it is most likely a piston problem as any nick in the knife edge will eventually be rotated somewhere else on the seat as the piston rotates slightly and itwill often leak in the old location. Alternatively if the stem is slightly off center, you will end up with two seating grooves over time and they will leak at the two points where they intersect.

Hi DA and Couv,

My technician replaced my MK10 seat and the IP was normal and holding. After 10 dives, the IP had bumped up to maybe just over 140 and the needle didn't appear very stable--perhaps a tiny bit of creep. I told the technician to please check carefully the piston edge, but he was very confident that the problem was the seat itself. He said there are two types of seats, each with a slightly different base shape (I believe he said something like one of them is a bit convex). He said my MK10 likely needed the "other" one, and so he replaced the seat again. On my first dive with the new seat, my MK10 was now whistling with every breath, at least when the tank was full. The whistling seemed to disappear gradually as the tank pressure went down. I told the technician about it and he said it was "high pressure" whistle and that a minor adjustment would fix it. We didn't check the IP again, but will do so prior to my next dive.

He said the piston edge looked fine, though I'm not 100% certain he actually looked at it.

This is where things stand. Never had such a headache with an MK10 before.

 

[redacted]

It sounds like your piston knife edge is fine. A problem there will show up as readily noticeable creep. Balanced pistons sometimes just want to whistle. Something about harmonic resonance involving the spring and the HP o-ring. Lubing the HP o-ring real good and flipping the spring often corrects, for a while at least.

Current Mk5/10 HP seats come in three different heights which give the tech a way to adjust IP without removing the piston. It sounds like you experienced some additional break-in after the service.

 

[halocline]

He probably put one of the old style flat seats in your reg, which were thought to contribute to whistling. The newer style seats have a conical shape which is supposed to eliminate the whistling. What you need is the conical seat and a piston edge that will mate with it. Since the newer seat presents a 3D shape to the piston edge, if the piston is not absolutely round it will not seal against the seat as effectively. A flat seat could theoretically seal with an out-of-round piston.

The problem is that I can't think of any reason that the piston would be out of round except for two things; 1) it got nicked or dinged, in which case you need a new piston, or 2) it's flared out a little at the edge from years of use. I have seen what looks like a tiny bit of flare on one of my MK5 pistons, but it's so slight I thought it was an optical illusion. I have a guitar maker friend with a nice accurate micrometer, but I'm not quite obsessive enough to take the piston out, bring it over to his shop, interrupt his work, just to see if the piston has flared .001".

Anyhow, I've had some IP creep problems with a MK10, and a very careful cleaning/inspection of the piston and a new (conical) seat took care of it. If you want to get really geeky with the tech, ask him to remove the piston so you can look at the edge with a dissecting microscope or a jeweler's loupe, and get someone with a micrometer to check for roundness and flare; it's easy to do both. If the piston is toast, you might be able to find a new one, but it might be easiest to see if a machine shop could put a new edge on it. I have no idea how realistic that is. You could probably clean up the edge by hand if you had the right kind of abrasive cone to fit inside the piston, a piston bullet tool to protect the edge while you sand/polish the outside, a little jig (a board with a hole drilled by a drill press the same diameter as the piston shaft) to hold the shaft still while you CAREFULLY "lap sand" the edge itself, and a spare piston for when none of this works.

Probably there's a little wear in the piston but it will still work with a conical seat once it's set. You can help "tap" it in place by tapping the purge a few hundred times with the reg pressurized; not enough to start a big flow (doing that repeatedly would really freeze the piston) just enough to bump the seal.

One other thing, and AWAP will confirm this, is that MK10s seem to have a slightly "mushier" seal than MK5s. Both my MK10s drift a little but the MK5s are rock solid. I don't think it makes any difference, and we're only talking about a few PSI.