Complete 1st stage failure (scubapro MK5)

[Leicamshooter]

While working on ditch and don drill today, I had a complete failure of my 1st stage scubapro MK5. There was a very loud pop/shrill behind my head. On the surface I saw that the swivel portion on my scubapro MK5 had completley snapped off. I'm going to post two pics of it, and maybe someone can tell me if this is an easy fix. I just had the reg serviced three weeks ago by my LDS. The repair guy said it looked to be in great condition. Is it worth fixing, or should I move on. What could have casued it?

Thanks!
G Medina

 

[HilaryRN71]

Interested in some more details, you heard a loud pop? Were you able to get ANYTHING (air) from your second stage at this point? How did you handle it?

 

[Leicamshooter]

I was in about 15 feet of water. There was no air comming from my 2nd's becasue they were attached to the swivel LP port section that snapped off. I looked around, saw my buudy was a ways off, and made a slow accent to the surface, exhaling all the way up. I think I would of been a bit more afraid if it had happened at 90 feet.

Looking inside, I can tell that the connection sheared off. I hear parts are hard to find for the MK5.

 

[Ben_ca]

Overtorqued?

 

[redacted]

That looks like it is one of the old brass turret bolts. They are very vulnerable to failing in the mode you experienced. My 1997 schematic for the Mk5 has Scubapro calling for the brass versions to be replaced by a stainless steel version that is common to all the Scubapro balanced piston regs. Seems to me that some tech in the past 9 years should have caught that and made the change.

It is definately worth fixing if you can find a good tech.

 

[DA Aquamaster]

Yep, definitely looks to be an older brass swivel retianer.

The brass swivel retainers were prone to damage from being over torqued and were also potentially able to be damaged if excessive stress or impact occurred to the swivel turret.

The older brass retainers require a more or less normal hex socket to remove although you have to grind off any taper on the end to ensure it has adequate bite. So it's basically impossible for a tech to miss that it is brass and not one of the newer stainless retainers that requires an allen wrench to remove or install.

Consequently, it would appear that during the last annual service it was either not removed (and the o-ring between the swivel cap and turret was not inspected/lubed/replaced or the tech serviced the o-ring and then re-installed the brass nretainer rather than replace it with a new SS retainer.

Either way, talk to your tech about it -although it is very likely he was not aware of the need to replace the retainer. Scubapro does not cover servicing their older regs in their tech seminars and while they used to offer a "vintage" class on techniques for older regs, I have not seen one offerred lately. Consequently, that type of information tends to get passed down in house from old techs to new ones and if the dealer is new or tech turn over has been high, that information exchange won't occur.

The last Mk 5 schematic (12/97) mentions the need to change the retainer in a service note on the page, but in practice these tend to be small hard to read print in the service manual. Plus the Mk 5 is so simple to service that there is nothing that prompts a tech to check the schematic for assembly assitance, to it is often skipped. And, it has been over 10 years since the change was made and it would not be uncommon for a tech to be generally unware of the need to change the swivel retainer and regularly used and serviced Mk 5's have usually been updated already so it is not always an issue.

SP also has a tech website, but they do a very poor job of keeping it updated with incredibly long delays before service bulletins are posted and again there are no reminders to inspect and check for needed updates on older regs when they come in.

As an aside, in the late 1970's and early 1980's Scubapro had a Mk 9. It was basically a Mk 10 but with a solid non swiveling swivel cap and turret for divers who did not trust swivel turrets. It was not very popular and is quite rare, as if properly updated and serviced, swivel turret separation is virtually unheard of.

 

[Couv]

I recently bought a MK10 on ebay and it also has a defective swivel retainer. I was looking through a parts list and indeed, the retainers are either brass or stainless steel (inox). The illustrated parts list gives the torque value as 70 in lbs for inox and 35 in lbs for brass. The parts list I have is dated 02/01 (I assume that is Feb 2001) so I had a look at some of the other SP 1st stage diagramsand to my surprise all of the regs with swivels (MK10, MK18, MK20) have the same item with the same part number.

If this was a known problem with the MK5 I wonder why they chose to use the same retainer (I am assuming it is the same as I do not have a parts list for the MK5)

DA, was there a material other than brass or inox used in this application for the MK5?

Thank you,

couv

 

[DA Aquamaster]

The Mk 5 used part number 10-105-102.

The Mk 10 and 15 used 10-500-103, which was also brass, but slightly heavier and with the center cut for an allen wrench.

The Mk 18, Mk 20, Mk 25 and Mk 25T all use the stainless steel 10-500-104 retainer

I have not checked latelyu nut I am pretty sure the only retainers you can get now are the stainless version.

The problem was not the strenght of the material in the intended use but rather the fact that you could over torque the retainer which led to stretching, cracking and breakage. In short it was a tech problem, not a design problem. Switching to a retainer that used an allen wrench was a good news bad news thing. The good news was that if a tech was not going to properly torque it, he was more likely to use a standard L or T shaped allen wrench which natually limited the torque that could be applied compared to a socket and ratchet. The bad news is that to properly torque it the tech now needed an allen head socket to use the torque wrench. Since it really was in the end a tech problem, switching to stainless steel was the solution to make it more Conan the Technician proof.

As far as replacing a brass retainer, that should be done, not because it may break due to a "defective" design" but because you don't often know the service history of the reg and whether the retainer has always been properly torqued.

Scubapro has had some torque wrench ignorant tech issues recently that indicate their tech training could be better, but on the other hand their tech training is still better than most other company's training - the difference is that SP regs tend to stay in service long enough for potential tech induced fatigue problems to become actual problems. We are after all talking about a Mk 5 - the last of which was produced in the early 1980's and the first of which was produced in the mid 60's.

 

[oxyhacker]

This is a well known problem, and definately the one weak point on an otherwise fantastic 1st. However it is entirely the result of inept servicing.

Overstressed pivot bolts can often be spotted during the visual parts inspection that should be an essential part of any reg overhaul. They'll be "waisted", that is to say, narrower, in the overstressed portion, with the threads being further apart due to the stretching.

 

[Couv]

Spot on Vance and DA,

Inept is the key word. A torque wrench is an essential tool in anyone's tool kit; remember to have it calibrated annually and one should always pull rather than push on the wrench to get the most accurate measure.

DA, the -102 and -103 do not appear on the drawings I mentioned earlier. This makes sense if the -104 is inox and the only replacement available. The torque value for the brass unit would be for reference should the re-builder need it.

I think the OP should have a word with the LDS who rebuilt three weeks ago.


couv