scubahorse
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Any one know the differents between SP MK20 and newer MK25? What about the MK20 with black coating? Thanks.
SCUBA PRO from MK20 to MK25
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scubahorse once bubbled...
Any one know the differents between SP MK20 and newer MK25? What about the MK20 with black coating? Thanks.
There's not a lot of difference between the two. The MK25 has the anti-freeze bushings and a few more refinements. I'll let somebody else more knowledgable than me elaborate.
I think you're refferring to the ultra light model (black coating.) The first stage is made of aluminium as opposed to brass. This created lots of corrossion problems between the hose fittings and the first stage ports.
The Mk 25 offers an externally adjustable intermediate pressure while the Mk 20 relies on the traditional Scubapro design using shims to adjust IP.
You can upgrade a Mk 20 to Mk 25 status if you prefer but it really is not worth the bother as they are otherwise identical. There have also been a few small design tweaks and some minor styling changes throughout the evolution of the Mk 20 and Mk 25.
For example the ambient pressure chamber holes have gotten larger over the course of Mk 20 production and the body around the piston and ambient pressure chamber has gained a bit in surface area to improve heat transfer a bit in the Mk 25.
The yokes on the newer Mk 25 models also have a black rubber coating on them that I suppose helps prevent the chrome from getting chipped.
The Ultralight Mk 20 and Mk 25T use a titanium first stage body and yoke. They make some small degree of sense for a traveling diver but cost a ton of extra money for the slight weigth reduction. And when you hit the water you end up adding more lead to offset the decreased weight of the first stage anyway. The suitabilty of titanium and it's durabilty over time is not really known yet and brass is preferred by just about everybody for very high O2 nitrox mixes.
Both use the Thermal Insulating System that is designed to work in 50 degree water, which is the main problem, the cold water encounterd by most cold water divers is a lot colder than 50 degrees. (Scubapro needs to start testing their equipment in places other than the tropcs - they can come to my neck of the woods and dive in an cold alpine lake if they like.) I have heard about a MK 25 AF that is supposed to be an improvement but I have not yet seen one.
As far as improving the freeze resistance of the Mk 20 and Mk 25, you can insure that the bushings and shims are in place to isolate the first stage spring from the piston. You need to insure the parts in the ambient chamber are coated in cristo lube, and you can decrease the intermediate pressure to around 120-125 psi instead of the nominal 140 psi. This will reduce the flow rate a bit and help prevent the first stage from freezing up.
One of the reasons for the Mk 20/25's tendancy to freeze is that it has an extremely high flow rate.
I have never had a problem with my Mk 20 freezing up and yet have had a very experienced and air sipping dive buddy freeze up on every dive with his new MK 25.
You can upgrade a Mk 20 to Mk 25 status if you prefer but it really is not worth the bother as they are otherwise identical. There have also been a few small design tweaks and some minor styling changes throughout the evolution of the Mk 20 and Mk 25.
For example the ambient pressure chamber holes have gotten larger over the course of Mk 20 production and the body around the piston and ambient pressure chamber has gained a bit in surface area to improve heat transfer a bit in the Mk 25.
The yokes on the newer Mk 25 models also have a black rubber coating on them that I suppose helps prevent the chrome from getting chipped.
The Ultralight Mk 20 and Mk 25T use a titanium first stage body and yoke. They make some small degree of sense for a traveling diver but cost a ton of extra money for the slight weigth reduction. And when you hit the water you end up adding more lead to offset the decreased weight of the first stage anyway. The suitabilty of titanium and it's durabilty over time is not really known yet and brass is preferred by just about everybody for very high O2 nitrox mixes.
Both use the Thermal Insulating System that is designed to work in 50 degree water, which is the main problem, the cold water encounterd by most cold water divers is a lot colder than 50 degrees. (Scubapro needs to start testing their equipment in places other than the tropcs - they can come to my neck of the woods and dive in an cold alpine lake if they like.) I have heard about a MK 25 AF that is supposed to be an improvement but I have not yet seen one.
As far as improving the freeze resistance of the Mk 20 and Mk 25, you can insure that the bushings and shims are in place to isolate the first stage spring from the piston. You need to insure the parts in the ambient chamber are coated in cristo lube, and you can decrease the intermediate pressure to around 120-125 psi instead of the nominal 140 psi. This will reduce the flow rate a bit and help prevent the first stage from freezing up.
One of the reasons for the Mk 20/25's tendancy to freeze is that it has an extremely high flow rate.
I have never had a problem with my Mk 20 freezing up and yet have had a very experienced and air sipping dive buddy freeze up on every dive with his new MK 25.
ElectricZombie
Contributor
Ditto what DA Aquamaster said.
The black Mk20 is the Aluminum version...stay away from this model. ScubaPro has had a lot of problems with the Aluminum 1st stages because they are not suitable for such stresses.
The black Mk20 is the Aluminum version...stay away from this model. ScubaPro has had a lot of problems with the Aluminum 1st stages because they are not suitable for such stresses.
OP
scubahorse
Guest
Thank you very much. It is really helpful. I will print it out and put it into my dive log.Actually, Scubapro specifically recommends not lubricating the piston stem inside of the ambient chamber because the grease provides nucleation sites for ice. Only very small amouts of lubricant are to be added to the piston o-ring.
Other than the afore mentioned external adjustment, there are numerous changes to the Mk25 piston specifcally addressing cold water performance. This includes changes in material and design for two parts in the bushing system, several changes to the piston base cap, and mirror polishing the piston stem. I haven't heard whether or not these changes really help, but the piston upgrade is available for the Mk20.
Other than the afore mentioned external adjustment, there are numerous changes to the Mk25 piston specifcally addressing cold water performance. This includes changes in material and design for two parts in the bushing system, several changes to the piston base cap, and mirror polishing the piston stem. I haven't heard whether or not these changes really help, but the piston upgrade is available for the Mk20.
That's interesting to hear. We (me and my Scubapro tech/dive shop owner/dive buddy) dissected his brand new recently delivered free flowed on every coldwater dive it ever made MK 25 and found the remains of some type of largely dried out white lubricant. We removed it and left the interior of the ambient pressure chamber, the spring and piston clean but it still free flowed as badly as before.
Neither my Mk 20 nor Mk 25 has ever freeflowed at all in well over 200 dives.
Unlike my MK 20 or MK 25, his MK 25 also has flutes around the body where the piston is located. I suspect this is for improved heat transfer. Would this be a MK 25 AF?
Personally, I am a really big fan of the MK 10 and it's silicone grease filled SPEC system.
That's the Mk25AF, its a new model and the chamber around the big end of the piston looks like something out of the Borg.
The TIS MK20/25 bushing garbage is crap. It is what has created the need for the "special" piston ring, as the ability of O-ring to seal is compromised by the screwball bushings (plastic, even) and they are subject to wear.
It also fails to solve the problem, at least completely. The solution to freezing problems is to isolate the water from parts that are cooled by adiabatic expansion and must move under those conditions. That simply can't be done with "TIS bushings" or anything else.
It is not a design suitable for ice diving, and never will be. But by God, SP can drive up the price of both the regs and their upkeep this way.
The only real difference of note between a Mk20 and 25 is the external IP adjustment, which, by the way, must be made with the stage DEPRESSURIZED. I wouldn't spend 25 cents to upgrade a Mk20.
The TIS MK20/25 bushing garbage is crap. It is what has created the need for the "special" piston ring, as the ability of O-ring to seal is compromised by the screwball bushings (plastic, even) and they are subject to wear.
It also fails to solve the problem, at least completely. The solution to freezing problems is to isolate the water from parts that are cooled by adiabatic expansion and must move under those conditions. That simply can't be done with "TIS bushings" or anything else.
It is not a design suitable for ice diving, and never will be. But by God, SP can drive up the price of both the regs and their upkeep this way.
The only real difference of note between a Mk20 and 25 is the external IP adjustment, which, by the way, must be made with the stage DEPRESSURIZED. I wouldn't spend 25 cents to upgrade a Mk20.
Agreed, the bushing system is crappy. There have been numerous changes in it over the years and they still don't seem to be able to get it right. BUT, my understanding is that they came up with this design because of the huge number of complaints regarding the pain-in-the-ass installation of the Mk10 stem o-ring deep inside the guts of the body. They apparently had too many come back from shops because of attempts to force the o-ring in. They also frequently were not replaced because of the difficulty in getting them out or a hack not knowing that it's in there.
If anybody's interested, PM me and I'll send you Engineering Bulletin #272 describing all of the changes in the Mk25.
In a conversation I had with SP's Technical Services mgr, he confessed that the "TIS" system really doesn't "insulate" anything, but the bushing is really there to break up the ice that does form on the piston.
With all of the little tidbits I've learned from SP Tech Services throughout the last few years, I do have to respect their engineering. They are very concerned with covering themselves during every combination of A, B, and C happening (regardless of how unlikely it is to happen). I think that's why you're always seeing new tweaks to their kits, but sometimes the condition they're fixing is so esoteric that even their people forget exactly why they put a little hole here or a tab there. Even so, I still wouldn't use them in cold water....
If anybody's interested, PM me and I'll send you Engineering Bulletin #272 describing all of the changes in the Mk25.
In a conversation I had with SP's Technical Services mgr, he confessed that the "TIS" system really doesn't "insulate" anything, but the bushing is really there to break up the ice that does form on the piston.
With all of the little tidbits I've learned from SP Tech Services throughout the last few years, I do have to respect their engineering. They are very concerned with covering themselves during every combination of A, B, and C happening (regardless of how unlikely it is to happen). I think that's why you're always seeing new tweaks to their kits, but sometimes the condition they're fixing is so esoteric that even their people forget exactly why they put a little hole here or a tab there. Even so, I still wouldn't use them in cold water....
Those are hard to get in? Huh?
Peterbilt has a very nice tool that makes it simple. Even without it, its not difficult - you just plug the short end, insert the O-ring sideways, and use the piston bullet tool to work it SLOWLY down until it slides in.
No problem at all.
Getting the old one out doesn't require any great expertise either, just care so you don't damage the groove.
The Mk10 is perfectly happy with a standard 70 duro EPDM O-ring in that location. I own several Mk10s and NONE have ever leaked using that O-ring in that location. The Mk25, despite using the same SIZE O-ring, is NOT happy with it, and will leak like bejeezus at tank pressures over about 3000 psi if you attempt to do that.
SPs "solution" to that is to use a 90 duro O-ring. The solution the problem THAT causes, that of excessive abrasion wear, which is the bug-a-boo of harder durometer ratings, was to go to Polyurethane for it. Since that O-ring is exposed to full tank pressure (its one of the few that is, and the ONLY dynamic O-ring that is), O2-compatability for Nitrox is a real issue.
That's not a solution, its a series of kludges to get around the original problem which they created by putting low-tolerance plastic pieces in there in the first place! And oh, by the way, the "inside" bushing can be inserted reversed (the outer one can't as it has a shoulder on it), and if you make THAT mistake the reg will leak like hades at virtually ANY tank pressure - so much for making it "stupid tech proof."
Oh, by the way, the MK10 is both simpler to rebuild (due to the lack of all that silly garbage in there that you have to keep track of) and breathes darn near as well as the Mk20/25 - one has to wonder if the "enhancements" were more to keep being able to file patents and keep clones away than anything else.
Peterbilt has a very nice tool that makes it simple. Even without it, its not difficult - you just plug the short end, insert the O-ring sideways, and use the piston bullet tool to work it SLOWLY down until it slides in.
No problem at all.
Getting the old one out doesn't require any great expertise either, just care so you don't damage the groove.
The Mk10 is perfectly happy with a standard 70 duro EPDM O-ring in that location. I own several Mk10s and NONE have ever leaked using that O-ring in that location. The Mk25, despite using the same SIZE O-ring, is NOT happy with it, and will leak like bejeezus at tank pressures over about 3000 psi if you attempt to do that.
SPs "solution" to that is to use a 90 duro O-ring. The solution the problem THAT causes, that of excessive abrasion wear, which is the bug-a-boo of harder durometer ratings, was to go to Polyurethane for it. Since that O-ring is exposed to full tank pressure (its one of the few that is, and the ONLY dynamic O-ring that is), O2-compatability for Nitrox is a real issue.
That's not a solution, its a series of kludges to get around the original problem which they created by putting low-tolerance plastic pieces in there in the first place! And oh, by the way, the "inside" bushing can be inserted reversed (the outer one can't as it has a shoulder on it), and if you make THAT mistake the reg will leak like hades at virtually ANY tank pressure - so much for making it "stupid tech proof."
Oh, by the way, the MK10 is both simpler to rebuild (due to the lack of all that silly garbage in there that you have to keep track of) and breathes darn near as well as the Mk20/25 - one has to wonder if the "enhancements" were more to keep being able to file patents and keep clones away than anything else.
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