Wayward Son
Contributor
What exactly does the plus upgrade do to the Mk10?
Mk10 Plus question
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It replaces the MK10/5 "hockey puck" or cave cone seat with the HP seat that is still used in the Mk20/25. Piston and seat retainer are also new to accomodate the new seat. I believe it is supposed to produce a more stable IP as you no longer have the knife edge piston cutting into the relatively flat HP seat.
The original Mk 10 used a flat seat and a knife edged piston. The Mk 10 Plus upgrade involves a new seat retainer to hold a new Mk 15/20/25 style concave seat as well as a new rounded tip piston.
The concave seat and rounded tip piston smooth the airflow into the flow through piston and improves the flow rate. It is very similar to the rounded tip piston/seat design used on mid production Mk 20's. It should be noted though, that this design did not last long in the Mk 20 as it lresulted in a very soft and indefinite lockup and, in service, the design was prone to excessive IP creep. Consequently Scubapro went back to using what was virtually a knife edged piston with the concave seat in late production Mk 20's as well as in the Mk 25.
The rounded tip psiton design did not fare much better with the Mk 10 Plus as the Mk 10 Plus was subject to a recall for seat replacement soon after introduction since the original seat material was not up to the job and seat life was quite short. In my experience, I never could get a seat to last an entire season (although admittedly I dive a lot) so after converting my Mk 10's to Mk 10 Pluses, I converted my Mk 10 Pluses back to plain old Mk 10's. There probably was some improvement in flow rate but the flow rate on the Mk 10 is fine already so I never noticed the improvement - but I sure noticed the shorter seat life.
To be fair, the latest seat material is fine and premature failure is not a problem on the Mk 10 Plus. However, the plain old Mk 10 with the old style knife edged piston now uses a redesigned concave seat anyway which also improves flow rate. I have not seen any definitive performance numbers but I suspect the improvement in flow rate with the Mk 10 Plus upgrade is relatively small compared to a recently serviced Mk 10 with a new concave seat.
So in short, I would not bother with the upgrade as the Mk 10 with the new concave seat is already very good and is also extremely reliable.
The concave seat and rounded tip piston smooth the airflow into the flow through piston and improves the flow rate. It is very similar to the rounded tip piston/seat design used on mid production Mk 20's. It should be noted though, that this design did not last long in the Mk 20 as it lresulted in a very soft and indefinite lockup and, in service, the design was prone to excessive IP creep. Consequently Scubapro went back to using what was virtually a knife edged piston with the concave seat in late production Mk 20's as well as in the Mk 25.
The rounded tip psiton design did not fare much better with the Mk 10 Plus as the Mk 10 Plus was subject to a recall for seat replacement soon after introduction since the original seat material was not up to the job and seat life was quite short. In my experience, I never could get a seat to last an entire season (although admittedly I dive a lot) so after converting my Mk 10's to Mk 10 Pluses, I converted my Mk 10 Pluses back to plain old Mk 10's. There probably was some improvement in flow rate but the flow rate on the Mk 10 is fine already so I never noticed the improvement - but I sure noticed the shorter seat life.
To be fair, the latest seat material is fine and premature failure is not a problem on the Mk 10 Plus. However, the plain old Mk 10 with the old style knife edged piston now uses a redesigned concave seat anyway which also improves flow rate. I have not seen any definitive performance numbers but I suspect the improvement in flow rate with the Mk 10 Plus upgrade is relatively small compared to a recently serviced Mk 10 with a new concave seat.
So in short, I would not bother with the upgrade as the Mk 10 with the new concave seat is already very good and is also extremely reliable.
OP
Wayward Son
Contributor
Thanks for the info. I'm buying a used Mk10/D400 from a friend, dunno if it has ever been upgraded or not. Asked but have not had an answer yet. My LDS says they can't get the plus kits for them any more, so I got curious as to what it did. I know George can service & tune these so no worries, just curious.
Scubapro may not sell the Mk 10 /Mk 10 Plus upgrade kits anymore (I have not ordered one in a few years so I don't know for sure.) Certainly in the past Scubapro has discontinued other upgrade kits. For example you can no longer get the actual upgrade kit to upgrade an Adjustable second stage to a Balanced Adjustable second stage. But it does not matter as Scubapro still sells all the required parts, they just don't package them together.
In the case of the Mk 10 Upgrade kit, Scubapro still stocks and sells all the parts for the Mk 10 Plus. So if you want to upgrade your Mk 10 to a Mk 10 Plus, have the LDS order the following Mk 10 Plus parts:
10-101-162 Mk 10 Plus Seat Retainer
10-500-114 Mk 10 Plus Piston Bushing
10-500-117 Mk 10 Plus Piston
and
10-550-041 Mk 10 Plus Annual Service Kit (which will have the seat and o-rings you need for the conversion.)
All the other parts are the same and can be used off your Mk 10.
SP dealers can also contact SP's tech support service to identify/obtain parts needed for conversions like this or they can just order the discontinued upgrade kit and let SP sort it out on their end. SP's customer service is exceptional in that regard.
And by the way, the D400 is an exceptional second stage - in my opinion the best ever made - and will offer unbeatable performance if tuned by someone who knows how to do it well.
If you really want the Mk 10 Plus upgrade and your LDS does not want to work with you on it by ordering the parts, send me a PM. You could send your reg here for the upgrade.
In the case of the Mk 10 Upgrade kit, Scubapro still stocks and sells all the parts for the Mk 10 Plus. So if you want to upgrade your Mk 10 to a Mk 10 Plus, have the LDS order the following Mk 10 Plus parts:
10-101-162 Mk 10 Plus Seat Retainer
10-500-114 Mk 10 Plus Piston Bushing
10-500-117 Mk 10 Plus Piston
and
10-550-041 Mk 10 Plus Annual Service Kit (which will have the seat and o-rings you need for the conversion.)
All the other parts are the same and can be used off your Mk 10.
SP dealers can also contact SP's tech support service to identify/obtain parts needed for conversions like this or they can just order the discontinued upgrade kit and let SP sort it out on their end. SP's customer service is exceptional in that regard.
And by the way, the D400 is an exceptional second stage - in my opinion the best ever made - and will offer unbeatable performance if tuned by someone who knows how to do it well.
If you really want the Mk 10 Plus upgrade and your LDS does not want to work with you on it by ordering the parts, send me a PM. You could send your reg here for the upgrade.
OP
Wayward Son
Contributor
Thanks much. I'm sure George can take care of it, but it's always nice to have options 
He is very good at tuning these, too. lots of experience with them. I'm looking forward to diving with it after he gets done with it.
He is very good at tuning these, too. lots of experience with them. I'm looking forward to diving with it after he gets done with it.
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