How does the Scubapro Mk 7 work?

[redacted]

Well, nostalgia and opportunity have overcome the threat of spousal abuse and I purchased another regulator - a Mk7. The idea that it might help my trim didn't serve to mitigate the criticism either.

While I wait for it to arrive, I've been looking at the schematic to ID unique o-ring needs and to figure out how the "honker" side works. Without a cutaway view, I'm having to guess at how some of these bits work. I assume the "stem" serves to meter some of the incoming HP gas thru the oscillator chamber. While tank pressure is high, it looks like the oscillator is probably pushed back against the oscillator retainer and does not move much. As pressure drops, eventually the oscillator spring pushes the oscillator toward an opening between the oscillator chamber and the piston HP chamber. And when you inhale at lower tank pressures, the additional drop in pressure allows the oscillator to move across the opening and cause a honk. How far off am I? I'm sure I will understand it better once it is spread out across the kitchen table. (Thankfully, wife/buddy tolerates that surprisingly well.)

Also, any suggestions on hardness for that oscillator o-ring (SP #01-050-322)? Looks to me like that sizes out to a 2-116. I'm debating between EPDM in duro 70, Viton in duro 75, or Nitrile in eithe duro 70 or 90. If extrusion of that o-ring is not a problem, I'll probably go with vitron for it's longer shelf life. I'm not planning on using this for nitrox and have no intention of retiring any Mk5s or Mk10s. I may even get to keep the never-been-wet Mk20/S600 as HER spare :07:

Thanks

 

[DA Aquamaster]

The business end of the Mk 7 is pure MK 5 and performance is essentially identical.

Your description of the honking end of the reg sounds close although I suspect the stem virtually shuts off the HP air flowing to the occillator until tank pressure falls below 500-600 psi where the spring is then able to lift the stem and allow air to flow to the occillator.

 

[redacted]

The business end of the Mk 7 is pure MK 5 and performance is essentially identical.

Your description of the honking end of the reg sounds close although I suspect the stem virtually shuts off the HP air flowing to the occillator until tank pressure falls below 500-600 psi where the spring is then able to lift the stem and allow air to flow to the occillator.

Thanks. It arrived today and the decals are still ledgible. I knew the Mk 5 was on the business end. I'll probably open it up this weekend and will let you know if I can figure it out. I originaly decided that the stem cushioned and limited the travel of the oscillator but then that face o-ring made no sense. Hope it will be as much fun diving it as it is figuring it out. That is one big chunk of brass.

 

[redacted]

Well, I had to peek. It looks like the "honker" mechanism is working entirely off the LP side. I guess it must be sensing IP drop. The oscillator spring is clearly in the 150 psi range, not HP. It looks like the stem and stem retainer must be used to adjust sensetivity. The oscillator face o-ring mates with a raised flat seat and the oscillator body looks to be a rather complex set of non-maintainable parts.

Good news is only leaks are coming from the ambient chamber and slight 2nd stage freeflow so I should be able to fix that tomorrow and put it in the pool

 

[DA Aquamaster]

Good news is only leaks are coming from the ambient chamber and slight 2nd stage freeflow so I should be able to fix that tomorrow and put it in the pool

Hmmm....hopefully. Sometimes a careless tech get in there and scratches the surface on the reg body when removing the HP o-ring. Alternatively, the reg can wear in that area with the result that you don't get the seal you need between the body, HP o-ring and stem.

 

[redacted]

Hmmm....hopefully. Sometimes a careless tech get in there and scratches the surface on the reg body when removing the HP o-ring. Alternatively, the reg can wear in that area with the result that you don't get the seal you need between the body, HP o-ring and stem.

Yeah, but that is part of the fun with ebay. 2nd stage ff cleared up with a little emery cloth on the LP seat to remove the groove. Z90 spg looks good & came with 2 HP hoses. And if I can't get the 1st to seal, then I'll only have 5 more kits than anyone in their right mind would need. She's about convinced me of that. :hanged:

 

[redacted]

Looks like the first stage leak was caused by deposit buildup in the ambient chamber encroaching on the sealing surface of the piston LP o-ring. It was quite rough but cleaned up nicely with a couple cycles of detergent wash and acid bath.

And the "honker" is working entirely on the LP side. Looks like it is sensing the drop in IP when you inhale on the primary 2nd which must be connected to the port in the piston retainer. I assume that as tank pressure falls, the IP drop as you inhale is greater. Looks like a pressure differential between the oscillator chamber and the stem chamber causes the stem to protrude further into the oscillator chamber. Exactly what makes the honking sound is still a puzzle but I heard it honk between 500 and 700 psi as I was purging it.

It's almost too bad. It would have made an interesting paperweight. Maybe one with the 2475psi yoke would be better for that.