Scuba Pro Mark 20

[DA Aquamaster]

I agree with you. I get pretty concerned that SP sends out very few service bulletins on it's regs and that we get left in the dark on most of these issues. They have a dealer/tech only website, they should use it and update it on a regular basis.

I'd also love to submit technical comments to them but that is not really an option. The shop owner has made comments about cold water performance issues but all it has gotten him is a sales rep who regards him as being disloyal.

 

[Scuba Tech]

Lost all my old schimatics in hurricane Ivan last year so this is from memory, dont remember what year.
The universal yoke nut came about as a change to the MK2 reg allowing one part to fit all then current 1st stages (MK 2/16/18/20).
Don't for one minute think it was for safty reasons!
Of the many failures i've repaired on these regs over the years this one I have never seen in person, would love to see one on my bench.
As for the solution of an upgrade to a MK25 this is essentially the same reg in this regard (differences being on the HP seat side of things).
Upgrade to a MK25 because you want a new reg and for no other reason!

 

[DA Aquamaster]

But I would be more comfortable with a little information on the nature of the design defect of the yoke nut that Scubapro believes is contributing to this failure of the body associated with overtorquing.

Actually, I was much happier with the idea that it was entirely a problem attributable to overtorquing...

We did formally get a service bulletin on the Mk 20 that goes into a fair amount of detail on the issue.

I find it a bit scary how many techs and shops may be doing service without using a torque wrench. Apparently, Scubapro may require the shop to have a compressor but has no requirement for a torque wrench.

They do now.

I think it is very significant that SP now also wants their dealers to certify that they actually own a torque wrench. SP is also offerring to provide shops with free torque wrenches if they do not have one. I find it extremely scary that some SP techs may not even have a torque wrench and it is pretty clear where SP thinks the problem lies with the Mk 20 cracks.

 

[moxie]

we lived or died on our torque wrenches and their calibration. Not using them when they are called for is an invitation to disaster.

 

[Guiseppe]

we lived or died on our torque wrenches and their calibration. Not using them when they are called for is an invitation to disaster.

Alright, I guess I am going to have to chime in, I have been quiet long enough.

Consider this –

Scubapro had a reported failure in California back in 2001, although they claim that after NOAA first alerted them to the problem, they took action. NOAA’s first failure was in reported in 2003.

They have also led us to believe that only NOAA has had a problem, therefore it must be NOAA’s tech’s who don’t know how to use a torque wrench. I've seen NOAA’s repair bench and they have a very nice Proto torque wrench and they do know how to use it.

But just like ScubaMoo said earlier, it’s not just a NOAA problem. There have been 14 failures that I have heard of and only 4 of those were NOAA reg’s. So now it’s not just one technician that can’t use a torque wrench. Now you’re talking about several certified ScubaPro repair facilities all of whom “can’t” use a torque wrench? Doesn’t make sense.

Of course, I have heard that some former ScubaPro engineers that have gone on to start their own company have said that basically the MK20 was a flawed design because there is no lip to keep the yoke nut from bottoming out and creating the kind of stress on the body that would cause a crack. It was also speculated that if you didn’t use a torque wrench and just snugged it down, you would be fine. But by torquing it to specs, you impact the first stage, possibly leading to the failure.

At least now, ScubaPro is acknowledging in their latest bulletin that all of this is basically true, except of course that their torque spec is too high.

ScubaPro also claims that they started using the new yoke nut, the one that has the collar to prevent that nut from bottoming out on all of their MK25 since they began manufacturing them (regardless of the part numbers on your schematics). I have opened up some pretty old ones, and so far they have all been the yoke nuts with the collar. Why would they have changed this part if they didn’t know there was a potential problem?

So DA, is seems this has gone from being an “urban myth” (your comments in March, 05) to being an honest danger to any diver using a MK20. And as it turns out there is a significant difference between those parts of the MK20 and MK25, unlike your previous statement (again 3/05) making it not such a “knee jerk” reaction by the government. And since it was ScubaPro that replaced all of the regulators, it wasn’t a waste of tax payers dollar, but a potential life saving “reaction”.

So for all of you that would still prefer to believe that it is just an over torquing problem, does it bother you at all that your reg, by design, is susceptible to this kind of failure? Just a little food for thought.

 

[moxie]

Well, got one MK20 done. No problem. Will get the other done in Dec. when annual service is due.

 

[DA Aquamaster]

was also speculated that if you didn’t use a torque wrench and just snugged it down, you would be fine. But by torquing it to specs, you impact the first stage, possibly leading to the failure.

We are talking speculation here by former SP engineers who started Atomic Aquatics after SP relocated some of their facilities right? So just to keep it in prespective let's make it clear that we are talking about speculation by persons with a bias, a possible axe to grind, and their own competing business interests to protect.

At least now, ScubaPro is acknowledging in their latest bulletin that all of this is basically true, except of course that their torque spec is too high.

SP paid for an independent third party analysis and based on that have concluded that if over torqued, cracking can occur. They are also consequently taking the initiative to upgrade Mk 20's to use the the current universal retainer nut. The accusation that the torque spec is too high is based on, as indicated above, speculation by persons with a bias, a possible axe to grind, and their own competing business interests. We probably ought to be fair and point out here that the effects of under torquing the fitting with any brand of first stage can result in a loose fitting and catastophic air loss during the dive, so going too low is an even worse idea.

ScubaPro also claims that they started using the new yoke nut, the one that has the collar to prevent that nut from bottoming out on all of their MK25 since they began manufacturing them (regardless of the part numbers on your schematics). I have opened up some pretty old ones, and so far they have all been the yoke nuts with the collar. Why would they have changed this part if they didn’t know there was a potential problem?

It's not a conspiracy, it's the result of standardization due to economics, to reduce the number of the parts inventory, and to facilitate easier conversion to DIN by eliminating the need for separate DIN kits for each model.

SP has in fact moved toward universal retainers that can be used in all their first stages. The lip allows that to happen as it eliminates any differences due to how the first stage is milled in that particular area. If you order a replacement for an older SP first stage you will get the current universal part rather than the one specified in the schematic. (For all of them except the Mk 5, which due to its design still requires a unique retainer.)

So DA, is seems this has gone from being an “urban myth” (your comments in March, 05) to being an honest danger to any diver using a MK20. And as it turns out there is a significant difference between those parts of the MK20 and MK25, unlike your previous statement (again 3/05) making it not such a “knee jerk” reaction by the government. And since it was ScubaPro that replaced all of the regulators, it wasn’t a waste of tax payers dollar, but a potential life saving “reaction”.

In March it was still an urban myth. Additionally, the idea that the Mk 20 has some sort of serious and fatal design flaw is still an urban myth. It does have a part that will lead to a failure if abused by over torquing so, at worst, all you can blame SP for is designing a part that was not completely idiot proof.

As for the Mk 20 and Mk 25 being essentially identical that is still the case. The two designs have always been evolutionary and if you look, a late production MK 20 has far more in common with an early Mk 25 or even a late MK 25, than it does with an early Mk 20. SP has always continually developed designs and made the improvements retrofittable into older models whenever possible. Before you start pointing fingers and crying conspiracy and accusing SP of "fixing" initially defective designs, consider that this evolutionary and unfrozen design approach is the same approach that every auto maker in the business uses.

So for all of you that would still prefer to believe that it is just an over torquing problem, does it bother you at all that your reg, by design, is susceptible to this kind of failure? Just a little food for thought.

I have yet to see a Mk 20 crack, but then I service the same Mk 20's every year and torque them properly so I know their maintenance history in most cases. And it is no surprise as out of thousands and thousands made and in service for over a decade, only 14 have developed cracks and none have resulted in fatalities. Let's not do a chicken little imitation here and blow it out of proportion.

And to give credit where credit is due, with the new retainer, the potential for them to be damaged through over torquing dissapears. SP is doing it voluntarily after their own privately funded third party investigation. They did not have to do that nor would they have to replace them for free so I think they deserve credit for addressing the issue as well as for taking steps to prevent problems that are developing in improperly maintained regulators. In my opinion it speaks to a committment to customer service through a willingness to do a free parts upgrade and to take steps to improve the quality of their technical services.

As a tech I would prefer they keep us updated about problems in a more timely manner. But to be honest given the tendency for some people to bash others based on limited or biased information or just plain speculation, I can't really blame them for wanting to keep their cards close to their belt until they have all the facts and are ready to present them.

 

[DA Aquamaster]

Last night I did a DIN conversion on a new, unused and never previously serviced Mk 20 made in 2001 (one of the last ones produced as a Mk 20). It was in all respects identical to the initial MK 25 except for not having the adjustable seat retainer. This included the yoke retainer which was in fact the Mk 25 style retainer with the lip.

The point here is that the evolution of the Mk 20 and 25 was gradual and constant and the defining feature that a made a Mk 25 a Mk 25 was the seat retainer and only the seat retainer. It was essentially the one additional improvement that prompted a numeric change to Mk 25 to identify what the evolved Mk 20 had become.

In this evolution I have seen a change in LP port turret design, a change in the size and shape of the holes in the swivel cap, a minor change in the chrome finish, 3 separate piston designs, a change in seat design, changes in the TIS components, the yoke retainer and finally, the seat retainer.

In effect, SP did not change the yoke/DIN retainer at the same time they changed the seat retainer and model number of the MK 20 and 25. Given that the change in yoke/DIN retainers occured during Mk 20 production it's safe to say no factory produced Mk 25 will have the old style retainer, but you have to inspect all Mk 20's to determine if they have the old retainer as most, but not all of them, will have the old retainer.

 

[oversea]

Last night I did a DIN conversion on a new, unused and never previously serviced Mk 20 made in 2001 (one of the last ones produced as a Mk 20). It was in all respects identical to the initial MK 25 except for not having the adjustable seat retainer. This included the yoke retainer which was in fact the Mk 25 style retainer with the lip.

The point here is that the evolution of the Mk 20 and 25 was gradual and constant and the defining feature that a made a Mk 25 a Mk 25 was the seat retainer and only the seat retainer. It was essentially the one additional improvement that prompted a numeric change to Mk 25 to identify what the evolved Mk 20 had become.

In this evolution I have seen a change in LP port turret design, a change in the size and shape of the holes in the swivel cap, a minor change in the chrome finish, 3 separate piston designs, a change in seat design, changes in the TIS components, the yoke retainer and finally, the seat retainer.



In effect, SP did not change the yoke/DIN retainer at the same time they changed the seat retainer and model number of the MK 20 and 25. Given that the change in yoke/DIN retainers occured during Mk 20 production it's safe to say no factory produced Mk 25 will have the old style retainer, but you have to inspect all Mk 20's to determine if they have the old retainer as most, but not all of them, will have the old retainer.

Hey, its good to see you got on it pretty quick.
Regards,
Justin

 

[Vie]

Last night I did a DIN conversion on a new, unused and never previously serviced Mk 20 made in 2001 (one of the last ones produced as a Mk 20). It was in all respects identical to the initial MK 25 except for not having the adjustable seat retainer. This included the yoke retainer which was in fact the Mk 25 style retainer with the lip.

Could you please post a picture of the yoke retainer (MK25-style, with the lip)?