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Why does a Scubapro Mk7 honk?

Discussion in 'Regulators' started by awap, Oct 22, 2004.

  1. redacted

    redacted Guest

    I'm hoping DA or one of the other Scubapro gurus can shed a little light on this.

    I've been examining my "new" Mk7 and I'm still not satisfied with my understanding of how the honker works. I think I have attached my attempt to diagram a cross-section view of the honker mechanism. It consistes of a high pressure chamber in the upper left and a LP chamber which I labeled a three subareas; A, B, and C. The classic balanced piston regulator side which I did not picture is just a funny looking Mk5. Slap it on a full tank and turn the gas on and the high pressure pushes that unbalanced piston (stem) in the HP chamber downward pushing the oscillator down into chamber C leaving chambers A and B as one (A&B). The double ended arrows in the oscillator are small holes which I asume allows chamber C to balance with A&B at the intermediate pressure. So LP gas LP gas flows from the LP chamber of the "Mk5" into chamber A&B and it works just like any other Mk5 but weight about 4 pounds. As HP decreases, the stem withdraws into the HP chamber until supply pressure falls to about 400psi and it starts honking loud enough to wake the dead and your buddy. How & why?

    In trying to fugure out what is happening, I got out the light and magnifying glass to see if I could find another LP opening directly into chamber A. There is not another LP opening. I was then concerned that the o-ring on the face of the oscillator could seal against the surface on the body and seperate chanber A from B. It can!! With dust cap off and no pressure, I tried to suck air thru the LP hose and it was sealed up tight! I'm going to spend some time in the pool this E/W and empty a couple pony tanks just to see how this thing breaths as tank pressure fally from 500 psi to less than IP. Since they call it an oscillator, I'm assuming that at low pressure, it is moving back and forth (seperating and reconnecting chambers A and B) fast enough to not interfer with the comfortable flow of breathing gas to the primary.

    I'm also guessing (but pretty sure) that the source of the honking is inside the oscillator. Although the SP schematic shows the oscilator as a single part, it is at least two rather large hunks of brass screwed together. I gave a half- hearted attempt at unscrewing them but it was tight enough not to unscrew easily so I decided not to mess with it (yet). So I'm thinking that the honk is generated by something inside the oscillator that is operated by gas flowing from chamber C into chamber A when chambers A and B are momentarily seperated by the o-ring on the face of the oscillator.

    So, anybody out the old enough and techy enough to know?

    I'm not able to see the attachment in the preview so here's hoping...
  2. ShakaZulu

    ShakaZulu Great White

    # of Dives: 200 - 499
    Location: San Diego, CA
  3. redacted

    redacted Guest

    On the design of the oscillator, only one hole in side of oscillator and it does not pass air. I suspect it is to engage a pin spanner. Two holes on the outside of the rear (chamber C) of the oscillator also do not pass air. I suspect they serve in positioning/tightening the two brass parts that are screwed together. The center holes in the face & rear pass air readily when you blow/suck with no noise and must serve just to balance the chambers. I suspect that the noise is made as gas passes from B to A as the oscillator oscillates opening and closing the flow of gas between those two chambers.

    You can "feel" the noise in the breath and in the second stage once it starts. If you sip the breath real slowly, it will not honk. You must breath with a fair to normal level of vigor. While I think WOB increases a bit once the vibration starts, it does not get uncomfortably difficult in shallow water. I hope to never try it very deep. I breathed the pony down to its last breath 3 times without any problem. I guess it could best be used as an alarm clock for for rest stops.

    Anyone else using one of these or am I the only one? There seems to be a plentiful supply of them on ebay. Do you think my wife/buddy would let me get on more - just for the extra SPG that comes with it, of course.
  4. bnelson

    bnelson Divemaster

    bringing this one back alive, i'll take a stab at it

    the HP in looks like it engages that pin when pressurized. the pin probably doesn't "push" what you called the oscillator down, but keeps the oscillator from moving (when the HP pressure is what we'll call "full"). once the HP pressure drops to a point we'll call "empty", the pin retracts, and the oscillator is free to move about the cabin, but remains stationary (i think) until something happens.

    when something happens, like the intermediate press. drops (when you breathe), it looks like the oscillator will probably move towards the "LP out to primary" orifice. since the IP will only drop a certain amount before the HP valve opens, once the HP valve opens, the IP will jump, pushing the oscillator back towards it's quarters. the oscillator probably just vibrates back and forth causing harmonics, probably similar to the ones MK25s are prone to.

    the o-ring at the top of the oscillator is probably to ensure there's a patent orifice for gas to travel through (if ever that o-ring were to set, the pressure buildup in the chamber would force the oscillator back down..)

    i doubt that gas is travelling through the oscillator (plus i don't see any path), i think it's more likely the oscillator makes use of the teeter-totter of the IP balancing act to vibrate back and forth.

    it's probably hell on that o-ring on the oscillator, i'd like to see it after a few years of heavy use. failure of the o-ring would probably just result in diminished effectiveness of the honker (but it would probably sound twice as hideous..)

    hope this makes sense and is not completely wrong
  5. aikiguy

    aikiguy Captain

    # of Dives: 50 - 99
    Location: On the blue parts, not the brown or green parts.
    I have one of these got it free of course, and would like to take it apart and play with it a bit.

    Anyone know where I can get a schematic?

    Are rebuild kits available for these?

    I don't plan on diving it, but might make it into a shop reg for compressed air delivery, or maybe put it on a tank on the dock with a long hose for bottom cleaning and generally looking at zincs etc.

  6. aikiguy

    aikiguy Captain

    # of Dives: 50 - 99
    Location: On the blue parts, not the brown or green parts.
    Now I am looking for a rebuild kit.

    Any ideas? Already tried E-bay, no luck....

  7. CaboJim

    CaboJim Barracuda

    # of Dives: 500 - 999
    Location: SoCal
    Just google scuba pro mk 7, you'll find a schematic in pdf form....
  8. halocline

    halocline Solo Diver

    There's an ebay seller in Houston that had a rebuild kit listed recently. I wonder how it differs from the MK5 rebuild kit. I know who would know.....
  9. redacted

    redacted Guest

    Either a Mk5 or Mk10 kit will get you most everything you need except for a few o-rings. The oscillator uses a -014 as a seat on the oscillator and a -117 on the its body. The HP feed to the honker take two -008 (preferably higher duro but I've done fine with duro70/75. The oscillator retainer take a -022 which is the same as the piston head o-ring so you can move the o-ring from the piston head to the oscillator retainer as long as it is OK. The Mk5 kit will have 1 -022 o-ring. If you go with the Mk10 kit, you will also need one of those separately. Also, the piston retainer take a -024. Even with a Mk7 kit, many of these o-rings will not be included as SP kits rarely include static o-rings so in any case, you will be looking for some separate o-rings. One other catch is whether yours take a flat filter or a conical filter. The Mk5/10 kit will include only the conical filter but the Mk7 kit might include one of each.

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