MK-5 vs. MK-10

[DA Aquamaster]

The piston stems on the Mk 5 and 10 are perfectly straight rather than slightly belled like the Mk 20/25 pistons. Consequently the actual area of the knife edge on the end of the piston is not accounted for in the balancing of the piston. That results in a 4-6 psi drop in IP as the supply pressure falls.

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On the Mk 5 and Mk 10 if you look at the evolution of pistons in each over the years the internal bore diameter of the piston stem gets larger in both. Also the Mk 10 ends up with a concave shape in the piston head. That, along with the rounded seating edge and concave seat on the Mk 10+ gives it a much better flow rate.

Which is to say the 1988 numbers reflect late model Mk 5s and fairly early model Mk10s.

Generally speaking I think the Mk5 is a better reg at back gas pressures than a Mk 10, but a Mk 10 is probably better on a stage where you breathe it at depth to low pressures. And a Mk 10 Plus is more than adequate in either role.

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The mk10 plus had issues with the early seats but it now uses the same seats as the Mk25. And the pistons never had the issues that the Mk 20 pistons had, so I have no issues using them and prefer them to the Mk 5 and 10.

Part of that is because there are some seriously old Mk 5 configurations out there that are not practical to update (pistons, turrets, swivel caps, yokes, HP ports).

 

[halocline]

I would like to get a MK10+ conversion kit and convert one of my MK10s. I understand that the rounded piston edge is designed for more aerodynamic flow across the piston edge; i.e quicker response, less I.P. drop, and the current MK25 piston is truly impressive with it's tiny IP drop and rock-solid lock up. If MK10+s work like that, I'd convert all of mine. But, you often read about mushy lock up, like the middle generation MK20. Someday i'll spring for a MK10+ piston and seat carrier.

While it's fun to talk about the differences in all of these balanced piston regs, I think it's worth noting that in the general scheme of 1st stages, any of the SP BP regs perform admirably and the design has been one of the most successful in history. The simplicity and reliability is pretty remarkable, considering we're talking about decades-old regulators that you can pick up on ebay for $50, overhaul yourself, and dive for another few decades.

 

[ams511]

For those of you having problems with the IP in the MK10, do you have an older or new style body or doesn't it matter? I have some of each. Also how much would it cost to upgrade a MK-10 to a Mk-10+ and will it complicate DIY servicing?

 

[ams511]

On the Mk 5 and Mk 10 if you look at the evolution of pistons in each over the years the internal bore diameter of the piston stem gets larger in both. Also the Mk 10 ends up with a concave shape in the piston head. That, along with the rounded seating edge and concave seat on the Mk 10+ gives it a much better flow rate.

Generally speaking I think the Mk5 is a better reg at back gas pressures than a Mk 10, but a Mk 10 is probably better on a stage where you breathe it at depth to low pressures. And a Mk 10 Plus is more than adequate in either role.

Part of that is because there are some seriously old Mk 5 configurations out there that are not practical to update (pistons, turrets, swivel caps, yokes, HP ports).

I have (don't laugh) 7 MK-5's: 3 with 2 HP ports and 5 LP ports and the SPEC holes, 3 that has 2 HP ports and 4 LP ports non-spec, and 1 with 1HP port and 2 LP ports. How can I tell which have the prefered parts? I assume I could mix and match if I want. I know th 5 LP port are a plus but what about the spec holes? Good or Bad?

 

[DA Aquamaster]

The heavier yoke is obvious as are 7/16" HP ports and the 4 and 5 port lp port turrets. The piston is less obvious - they come in stepped and unstepped varieties (stepped is preferred and un stepped is recommended to remove from service) and the bore diameter got larger later.

SPEC holes are nice if you want to use silicone, not spec holes are larger and make rinsing a lot easier if you opt not to use silicone.

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Mixing and matching works fine in most cases but the tolerances between piston stem and reg body are vital. To much room leads to o-ring extrusion and "pinching", especially at high pressures (on both the mk5 and Mk 10.

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At BTS last year, SP had 8 mk10 plus upgrades left - so I ordered 4 of them, but the shop owner never got around to placing the order, which was incredibly annoying. In any event the upgrade kits are no longer available.

 

[ams511]

So if I understand you correctly, the answer is to proceed with caution. As for the MK-10+ , a person would either need to find a dealer with a kit or order the parts seperately (piston, seat retainer, and some washers, I think). Cost wise it would probably be cheaper to buy a used MK 10+ and sell off the MK 10.

 

[Zung]

Or stop worrying and test what you have. If you can find some that recover within a second or so after a purge with no creep, you may possibly live happily ever after with them, and rebay the rest.

The big plus I see with the MK5 & MK10's: you can get the Trident seats for a couple of bucks each, whereas the MK10+ will require you to find a source willing to sell you the original MK20/25 seats, or buy the the kits.

 

[DA Aquamaster]

It's not a matter of buying parts, new Mk 10 plus pistons and seat retainers are just not available from SP.

 

[Six2Life]

I have (don't laugh) 7 MK-5's: 3 with 2 HP ports and 5 LP ports and the SPEC holes, 3 that has 2 HP ports and 4 LP ports non-spec, and 1 with 1HP port and 2 LP ports. How can I tell which have the prefered parts? I assume I could mix and match if I want. I know th 5 LP port are a plus but what about the spec holes? Good or Bad?

I purchased some regs on Ebay and was going through them trying to decide what to keep and what to rebay.

I would recommend that you finish rebuilding all of the MK5's that you want to keep before letting any of the extras go. There is a chance one or more of the "good" MK5's might need an out of production donor part from one of the less desireable MK5's.

As a newbie DIYer myself I have had a much easier time rebuilding the MK5's to acceptable performance than the MK10's. 3 of the 4 MK5's I've picked up are now in good shape and ready to dive. The one that's not working was pretty much a basketcase anyways. Of the 2 MK10's I have one took quite a bit of fiddling with to get working and the 2nd one I'm still having trouble with.

In a way I don't see the increased parts availability for some of the major MK10 parts as that much of an advantage. The cost of something like a new piston is high enough that you'd likely be just as well off picking up another used 1st stage. Although with the way prices on these used regs seem to be slowly creeping up that may become more of a valid concern as time goes on.

 

[ams511]

As I mentioned before I have 7 MK-5's: 3 with 2 HP ports and 5 LP ports and the SPEC holes, 3 that has 2 HP ports and 4 LP ports non-spec, and 1 with 1HP port and 2 LP ports. Last night I took a look at them and it appears that as the lp ports increased so did the thickness of the yokes. To me the best thing would be to keep the non-spec regs (I don't need cold water performance in Miami) and replace the yokes and turrents from the spec regs. I just need to call around to get the trident parts and the o-rings and I will rebuild them all for practice.

For the people having trouble with the MK10's is this with the older style or the newer one?