SP MK 10 PLUS: please help ID

[redacted]

I've already removed all the shims. The spring should be the same, since the Plus was also available as a retrofit/upgrade with only the piston, the seat retainer and the seat.

I tried to remove the TIS to relube it as per the SP guide, but it opposed a very solid resistance. I'll try to remove the washer tomorrow; the MDS said something about protection against metal to metal contact between the spring and the body, but it wasn't ther with the non-Plus, and nobody complained.

Unless we decide to go skiing

Why did I upgrade these guys 14 years ago? The Mk5 locks up sooooo much better!

I don't think it is just the upgrade. I have 5 or 6 of each (Mk10 [no +}and Mk5) and I use mostly my Mk5s as IP just behaves better. My theory is that the Mk5 with its larger piston has a stronger spring to offset that force and any friction at the HP o-ring (same design in both) has a lesser impact. My Mk10s give me more IP swing from high to low tank pressure than my Mk5/7s. As soon as I find a din converter for a Mk5 I will probably retire my last Mk10. My Mk20s are little problem, They are just a little mushy on the IP lockup.

 

[DA Aquamaster]

Less IP change is one of the major advantages of a larger piston head and after a brief departure to smaller piston heads on the MK 10 and Mk 3, Scubapro went back to the larger head diameter.

 

[Zung]

Sadly, awap is right.

After the Mk10+/G250 #1 settled in, the IP crept up to 170 PSI over a 15' period. Seat retainer tight, no shim, piston edge smooth.

I removed the washer, the IP dropped to 160 PSI over the same period of time.

I dumped the whole thing in the bath tub, there's absolutely no leak. Then I let the air on for an extended period: the IP crept slowly to 180 PSI after a hour and stayed there.

Oh well, I guess this guy is a perfect candidate for a downgrade!

 

[redacted]

Sadly, awap is right.

After the Mk10+/G250 #1 settled in, the IP crept up to 170 PSI over a 15' period. Seat retainer tight, no shim, piston edge smooth.

I removed the washer, the IP dropped to 160 PSI over the same period of time.

I dumped the whole thing in the bath tub, there's absolutely no leak. Then I let the air on for an extended period: the IP crept slowly to 180 PSI after a hour and stayed there.

Oh well, I guess this guy is a perfect candidate for a downgrade!

I think I would do more troubleshooting before going with a downgrade. At a minimum, swap springs with one of the others to make sure the spring is good as it will continue to be used in the downgrade. While you are at it, put the seat and piston umder a magnifying glass and look for defects. If the seat looks good, I'd also put that seat and retainer in one of the other Mk10s and see if the seat performs OK in one with known good piston and spring. Hopefully that will made it reasonably clear what is causing the problem. Then you can decide; new spring, new seat, or downgrade upgrade (just get another Mk5).

 

[halocline]

That's the one with the new seat, right? You really should lower the IP to 140 or so and see if it still creeps. If you have no shims, no washer, and the IP is 160, something is really wrong with the spring (most likely) or seat, like it's the wrong size. On my MK10s with no shims the IP is never higher than 120.

Try a different seat, maybe the one that was in there before. As awap suggests, try a different spring, too. As far as inspecting the piston, if you have normal IP, a new, correct seat, and very slow creep, there's almost certainly some small imperfection on the piston edge, it doesn't take much. I use a 16X jeweler's loupe (like a watchmaker would use, any of those in your country?) and I bet you'll see some scratches.

The good news is that it doesn't matter if it creeps; 160 is way too high for a freshly rebuilt MK10, so you have to fix that no matter what. You might be surprised that the creep disappears with the right IP. I'm not sure why that is, but if I had to guess I'd say that the spring is under less tension and might be a little more stable. If that's true, it could conceivably result in more stable seating force. Seating force is the amount of pressure the piston is exerting on the seat in order to seal, it equals IP minus whatever the spring is pushing against the other side of the piston.

 

[Zung]

That brings me to another burning question i have for sometime: is it safe to take a good reg apart?

There has been diverging opinions expressed here that break down to:

1. Concentricity of the piston
2. Concentricity of the seat
3. Concentricity of the seat carrier

I think everybody likes the idea of cleaning the guts once in a while, but I'm not sure if that does more good than evil. I started marking everything, but at least the piston WILL rotate when you screw the cap back in.

Even though in this case, the 10+ has a rounded piston edge that doesn't cut the seat. I've looked at the old seat with a loupe (don't know the x-factor) and could barely see a trace.

I'll start by putting the old seat back and report to you guys.

PS: watchmakers: mattboy: are you talking about these guys? I think they're more the Ferrari type than the loupe type

 

[Couv]

OK, I'm not going to address the things that have been covered already, except one. The stem o-ring. Make sure it is a duro 90 and well lubricated. If that puppy is extruding, it will slow the piston down and allow the IP to rise. Next, try a different seat seal, the orange or amber washer (in some cases a -013 o-ring). If the washer is too think, it will prevent the seat retainer from bottoming out and due to the greater piston travel, the IP will have to rise to overcome more spring pressure. Remember, anything that compresses the spring more will make the IP rise. After you have confirmed the o-ring and hp seat seal are good, you can try something simple, like a small shim between seat retainer and seat. This will shorten the stroke of the piston, but make sure the seat is level. One way to check this is with a bit of putty, modeling clay or (may be called Plasticine in Europe). Put a very thin layer over the hp seat surface where the piston makes it's indentation (use a different color than the seat) and after cycling the reg a few times, remove the retainer and examine the putty. Is the impression evenly distributed? If not, then the seat may be warped or perhaps as you suggested the piston bent.

Awap has already suggested to start doing a parts swap, like the spring. If you do find the spring to be the culprit, as long as we are doing a fix it yourself; I'll let you in on another procedure that is not part of the Scuba Pro manual, but has been used by other manufactures (SAS) to solve a problem with IP….it's "shim to raise, shave to lower." Yep, you already know to add shims to raise the IP, but you've already removed all the shims-including the one under the seat retainer right? So if you know the spring is bad, you may as well try to shave off a bit of material. It is important to shave (on a grinder or sander) in a manner where the spring is still square.

I got a bit long winded (I'm at work and keep getting interrupted) so to summarize:
Try swapping parts with known good ones first.
Use a very, very thin layer of putty on the hp seat to check the piston indentation.
If the spring is found to be bad, shave it to reduce the IP.

Good luck and keep us posted.

Couv

 

[redacted]

I share your concern about unnecessarily disturbing the HP seat. In my box of used parts, most of the older style Mk5/7/10 HP seats that have failed have multiple grooves cut in them which eventually compromise the lockup. Unless I am going to replace the HP seat, I leave the seat in the retainer. So far this seems to work. I try to avoid unnecessary disassembly but I do end up treating the whistling piston 2 or 3 times in the 3 to 5 years I get out of an HP seat.

Be careful shimming between the HP seat and the retainer to lower IP. I tried to take a Mk5 down well below spec for use with an air tool. It worked a bit but somewhere around 90 - 100 psi, the piston would no longer pull away from the seat.

I think I would also work on the TIS bushing a bit more. It looks to me like that should make a 10 to 15 psi change in IP based on the thickness of the bushing on the Mk20. I don't recall any of my Mk10s having that bushing.

Edit: One other thought. In following this discussion, I was looking at a spare Mk`10 spring I picked up on ebay a while back. I remember it had a different part # than was shown in my 12/97 schematic. I just compared it to the springs in two of my Mk10s and it is the same diameter but about 2mm longer and about 1mm thicker material. It does appear to have the TIS coating like a Mk20 spring.

More Edit: Got to looking some more and decided that that spare "Mk10" spring I bought may be a Mk2 spring. Point is, they could be swapped. A Mk5 spring would also fit the envelope.

 

[Zung]

couv

The trouble maker is the ******* (oxy's word) Mk 10 Plus. It has no seat seal at all; the seat is in direct contact with the main body of the reg, and has an o-ring in the middle for the sealing. The seat retainer is also in direct contact with the body. See the cutaway below which is clearer that the one I previously posted.

The stem o-ring was the one with a red stripe that came with the official SP kit for the 10+. After talking to my MDS, I replaced it with a known Duro 90 Buna-N -010 (I don't do EAN). And there's nearly a dollard's worth of Christo in both grooves (piston head too). No change.

Just now, I put the old seat back, and there's no big changes, it just takes less time to stabilize: 15' to 177 PSI instead of an hour, no "Spring Centering Washer".

So that leaves shimming the seat and shaving the piston...

awap

You maybe on to something!
Even though the reg is in good shape and doesn't appear to have a lot of use, the seller, or someone before him, may have assembled it from misc. parts to make a quick buck, or just out of ignorance. The missing turret bolt washer is another clue. The piston and the seat retainer seem to be original, but the spring may have been swapped.

I'll try swapping the spring and report back. Meanwhile, could you please measure the lenght of both types of springs you have? Thanks.

 

[Zung]

I swapped the spring from Mk10+/G250 #2, no change.
Then spring + piston from the same: IP now down to 155 PSI!
This combination in the original body is worth 144 PSI, so there's still a little something, but the bulk of the problem is gone!
So I have to find another piston, or, better still, a downgrade kit!:depressed:

Thanks to all who helped!