Scubapro MK20 vs MK25

[JKSteger]

I just wanted to pass along some information that I received from my Scubapro Tech today. I took in my MK20/G250 to get the IP adjusted and the "cracking" pressure of the G250 set to specs. that I would prefer. While there the SP tech changed out some part for free because Scubapro said that over torqeing (he showed me his torque wrench and said that I wouldn't believe the number of techs who don't use one even though SP service manual says they are required) the part could/would lead to cracking. (the only thing I noticed changed was the little black skirt thing has 2 slots now instead of the 3 slots it had before, although, he did show me the part he took out and replaced with the new one....tech stuff). After all adjustments made (adding "shims"?) I asked how much a MK25 1st stage would run me.

His answer suprised me! He said that he had already replaced something (what, I do not know--the spring, seat or piston) on my last anual service and that my MK20 was basically a MK25 "under the hood". He then showed me where he could replace a piece on top that would allow him to adjust the IP a little bit w/o having to take it apart, (he said I didn't need it). He also said he could add the metal turrent "fins" for $45.00 and a new LP swivile for more $$$.

He basically said that other than a few cosmetic and a new piston, spring or something that the two were identical "under the hood".

He said that ScubaPro probably needed to get a new model out after the MK20 so people would rush out and get the "new model" and chunk their MK20's.

I thought it was interesting. I just wanted to pass this along to thoes who have MK20's and were thinking about upgrading to the MK25's.

...I have no reason to doubt he is telling the truth. He could have easily tried to sell me the MK25 1st w/o any of this knowledge.

Jeremy

 

[Vie]

He basically said that other than a few cosmetic and a new piston, spring or something that the two were identical "under the hood".

I thought this was relatively common knowledge? Early MK25s looked practically identical to late-model MK20s; basically a MK20 could be upgraded to a MK25 by replacing the one piece seat retainer plug with three parts (spacer/adjuster screw/seat retainer) - this enables the IP to be adjusted via the adjuster screw on the MK25 without having to use "shims," I think. Later MK25s have the "ribbed" swivel cap, supposedly to increase resistance to freezing, and this changed the "look."

Otoh, the changes from the MK20 to the MK25 was evolutionary/gradual - LP port turret design, a change in the shape and size of the swivel cap holes, a small change in the chrome finish, three different piston designs, a seat design change, TIS components changes, yoke retainer and finally, the "defining feature" (which caused a designation change from "20" to "25"), the seat retainer.

Anyway, I'm sure DA Aquamaster will be along shortly to share his expert knowledge (and probably correct me).

 

[JKSteger]

I just thought that the MK25 had a little "better" performance. But what do I know?

I thought it was pretty cool how he explained a "formula" on the Intermediate pressure and depth. Evidently, there is a forumula that you can use to see how deep your IP setting is good to before you get a performance hit. So say if you set the IP to 130. You run this formula and see that the reg's performance will not take a hit until it gets to something like 291' or something.

Does anyone know what I'm grabbing at here?

Thanks,
Jeremy

 

[Scubakevdm]

The changes gave the reg better cold water performance, hence the AF (anti-freeze).

 

[Hoosier]

I think your tech tried to explain the upgrade kit from MK20 to MK25. It has been covered here by DA Aquamaster several tiems.

 

[JKSteger]

Thanks everyone, I wasn't aware that the "word" was out.

Jeremy

 

[DA Aquamaster]

Vie has it right. The defining feature that made a Mk 25 a Mk 25 as compared to a Mk 20 was the new seat carrier that allowed for an external adjustment of the intermediate pressure. Otherwise the Mk 20 and Mk 25 were, at that point in time, identical.

The Mk 20 itself underwent several detail changes over the course of it's production life, so earlier Mk 20's are increasingly different than the initial Mk 25. For example the Mk 20 used two previous piston designs before using the one that went on to be used in the Mk 25 (and this piston has since also underwent minor change with a mirror polished piston stem). The TIS system was also introduced during Mk 20 production so some are marked TIS and others are not - but all of them are readily upgradeable with most of the upgrade occurring automatically with the new parts included in the annual service kit.

The Mk 25 also underwent evolutionary changes with the adoption of a "universal" yoke or DIN retainer (actually introduced late in Mk 20 production), different swivel caps with progressively largeer and more oval shaped holes, with the last one being the current fnned swivel cap, and a new LP port turret.

What SP does with reg design is basically what car companies due with improvements to a particular model every year, with the difference being that SP normally makes the improvements retrofitable into older versions, which is a nice touch.

I agree that changing the designation from Mk 20 to Mk 25 was as much a marketing ploy as anything else as the Mk 20/25 is best regarded as one continual evolution of a single design. Since the first stage body itself did not change at all, and since all the changes were just parts added on to the body, a change in numbering was not really justified, but the rationale was that the design had evolved enough over time that a new number was warranted.

In my opinion, the only upgrade worth spending money on is the new composite piston (if you have the opriginal stainless steel piston or the slightly later brass tipped piston.) Dealer cost is $20 and it comes with the TIS bushing installed. It provides a much more solid lock up than the mid Mk 20 production rounded brass tipped piston in addition to offering more freeze protection. But if you wanted to, you could take the first Mk 20 ever produced and bring it up to the current Mk 25 production standard.

 

[JKSteger]

Thanks DA,
Jeremy

 

[Andrew Dawson]

Is there a chart with pics that shows the first MK20 all the way to the latest MK25?

Or just one for either of them?