Scubapro MK 15 History

[BillP]

Hi All:

I have a vague memory of the Scubapro MK 15 first stage regulator having a design problem that had to be fixed with a retrofit kit. Scubapro usually seems to keep products in their line for an extended period of time, but the MK 15 came and went pretty quickly. Can you fill me in on the details of the history of this first stage?

TIA,

Bill

 

[rainreg]

hello bill sorry it took so long to get an answer to you, the problem that i have run into is conflicting information from scubapro reps, I have tracked down more infomation on the mk15 and as I finish reading it I will get you an answer asap.

rainreg

 

[BillP]

Thanks. No hurry. Just curious.

Bill

 

[Tai Mo Shan]

Thanks. No hurry. Just curious.

Bill

The very first reg I bought was a Mk15.
Likewise, I have found that it seems to have disappeared off the map with Scubapro.
Can anybody suggest where I can get some spare HP seats for the regulator?

TMS

 

[DA Aquamaster]

Scubapro introduced a new concave seat design on the Mk 15 and had some initial problems with the materials used in the new seats and had to makes a couple changes before they got it worked out. All of the older seats were automatically replaced as a matter of normal procedure at the next annual serivce, but SP may have actually recalled some Mk 15's for immediate replacement - I'm not sure on that.

The Mk 15 is very similar to the later Mk 20 and Mk 25. The Mk 20 design was an evolutionary progression of the Mk 15 and just addressed a couple of issues that came up in service. So it is not that the Mk15 was defective or short lived, it was just a ground breaking reg that was additionally developed in a fairly short period of time. But as indicated above the Mk 15 did introduce concave seats and a much larger piston stem diameter which both improved flow rates. The Mk 15 also introduced a replaceable bushing system that allows tighter tolerances around the HP o-ring and prevents wear in this area. This allowed 300 BAR (4350 psi) service presures without problems with HP o-ring pinch.

The bushings in the Mk 15 were retained with a C-clip that was not popular with techs as it takes a longer and skinnier than normal set of snap ring pliers to remove and install this clip. The bushings were retained in the Mk 20, but they are held in place with spring pressure rather than with a clip and are easier to change.

The rear end of the Mk 15 was also all metal like the previous Mk 10 but the Mk 15 was substantially larger and heavier. The dull chrome finish was also a bit more prone to chipping off on the corners of the reg with impacts etc, so the Mk 20 incorporated a regulator body with much less (and un-needed) metal in this area covered with a rubber end piece that improved the cosmetics of the reg and, in conjunction with another scallop of removed metal on the bottom, reduced the weight significantly.

One of the plastic bushings in the Mk 15 was also permanently pressed into the body of the reg and this design was altered on the Mk 20 to allow this bushing to be changed. There was a problem with some techs (mostly non SP trained techs) attempting to remove this permanently installed bushing resulting in the need for either SP or the customer to pay for a new first stage body. Making it removeable made it much more idiot proof.

 

[Tai Mo Shan]

DA Aquamaster.
Many thanks for your two exceptionally informative messages.
I am developing a genuine interest in the servicing of my own regulators mainly because I live and cruise on my own trawler and often dive remote areas where there simply is no service support. I have already accumulated quite a good selection of the Peter Built inventory and I would dearly like to get the appropriate training and authoriozation from Subapro to be able to purchase spares etc.Very difficult, I know.
I took down my Mk15 after it came back from servicing and started free flowing. The main spring had sheared and I guess the subsequent mis-alignement of the stem had damaged the stem O ring (or at least I am guessing this is what happened.) I replaced the the spring and o-ring and the regulator seems OK but I have been unable to find anyone who can supply me with a new HP seat. Interestingly a small amount of air seems to be escaping from the pin hole in the HP cap. (Around the HP seat?)
Also I cannot find the upper bushing you refer to in your previous message. Where exactly is this supposed to fit. I am wondering if the people who serviced the reg left it out or something similar!
I am currently diving with the Mk25 which seems to be working fine.

Brgds

TMS

 

[DA Aquamaster]

The upper bushing in the Mk 15 is a white plastic affair that is pressed into the main body at the point where the piston stem enters the body on the ambient pressure side. It should be visible with the swivel cap removed. If it is missing it could be part of the problem with the leaking Hp o-ring and possibly with the broken mainspring.

The Mk 15 uses the older style Mk 5 / Mk 10 seat that uses a seat o-ring and seat bushing on top of the seat to seal the gap between the seat carrier, main reg body and the seat itself. There is another seat carrier o-ring on the base of the seat carrier, but this is partially redundant and does nothing to prevent air leaking between the seat and seat carrier and ultimately out the hole in the middle of the seat carrier. This hole is there to allow air to escape when installing the seat and to enable the tech to use air pressure to blow the seat out of the carrier when it needs changing.

If you have air leaking out the hole, the seat o-ring is either in need of replacement or perhaps it or the seat bushing is even missing entirely.

A broken mainspring is fairly rare and is usually the result of the spring being overshimmed (more than 3 shims total) and working outside its normal compression range. But I have noted Mk 10 springs tend to work harden with age, so it's possible the same thing could occur with a Mk 15 spring if the same materials were used.

If you have a trawler with a spare cabin aboard, there is no need to learn to do your own regs - I could be available as your own personal tech for a very reasonable annual salary.

 

[Tai Mo Shan]

The upper bushing in the Mk 15 is a white plastic affair that is pressed into the main body at the point where the piston stem enters the body on the ambient pressure side. It should be visible with the swivel cap removed. If it is missing it could be part of the problem with the leaking Hp o-ring and possibly with the broken mainspring.

The Mk 15 uses the older style Mk 5 / Mk 10 seat that uses a seat o-ring and seat bushing on top of the seat to seal the gap between the seat carrier, main reg body and the seat itself. There is another seat carrier o-ring on the base of the seat carrier, but this is partially redundant and does nothing to prevent air leaking between the seat and seat carrier and ultimately out the hole in the middle of the seat carrier. This hole is there to allow air to escape when installing the seat and to enable the tech to use air pressure to blow the seat out of the carrier when it needs changing.

If you have air leaking out the hole, the seat o-ring is either in need of replacement or perhaps it or the seat bushing is even missing entirely.

A broken mainspring is fairly rare and is usually the result of the spring being overshimmed (more than 3 shims total) and working outside its normal compression range. But I have noted Mk 10 springs tend to work harden with age, so it's possible the same thing could occur with a Mk 15 spring if the same materials were used.

If you have a trawler with a spare cabin aboard, there is no need to learn to do your own regs - I could be available as your own personal tech for a very reasonable annual salary.

I am beginning to wonder if my Mk15 is a locally produced hybrid or something similar. It doesn't appear to contain half the parts you mention!
The seat cap does indeed have the pin hole but as far as I can see from dis-assembly the nylon HP seat has just been pressed into place with no bushings or o-rings. The metal cap itself has an o-ring to seal it when screwed into place. The next component down is what looks like a stainless or chrome bushing with a shoulder which sits just proud of the end of the HP stem and, I guess, keeps the HP seat in place. I located the plastic bushing you mentioned but this doesn't seem pressed into place and readily came away with the stem o-ring.
Anyway, I will try to get hold of a Mk5/10 seat and see if it all works OK.
The next voyage departs Hong Kong for the Philippines at the end of the month but I regret we are somewhat booked up despite your very obvious qualifications!
We hope to get as far south as the Tubahatta Reef this time and also spend a few days at our dive school in Puerto Galera to complete the Dive Master course we began just before Christmas.

Brgds
TMS

 

[DA Aquamaster]

The seat o-ring should be between the seat and the metal bushing you found. If it is not there, that would be the source of the leak. The shoulder on the bushing goes inside the seat o-ring to center it.

There is also potentially a rubber sleave over the piston stem that is part of the antifreeze kit if your Mk 15 was so equipped. So if the part you found is soft and squishy that would be it. If it is hard plastic it is the bushing that should be both pressed and crimped into the first stage body. There is normally no way to remove them short of picking it out in pieces so I would be surprised if you have a loose one in one piece.

The Mk 5 and Mk 10 seats are similar in general design concept to the Mk 15 seat but the Mk 15 seat is much thinner.