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Discussion in 'Regulators' started by Jafo123, Apr 21, 2005.

  1. Jafo123

    Jafo123 Solo Diver

    # of Dives: 50 - 99
    Location: Hinton,Iowa
    I just bought a new ScubaPro 650 with a MK 2 plus first stage. Anyone using one of these? I'll be diving with it for the first time tonight in the pool for my drysuite training and was just wondering what to expect out of it. I'm a newbie and is only the second set I have ever bought the first set I had I purchased used. I'm also not a tech. junky so not real sure of what I was reading in the manual.

  2. Vie

    Vie Divemaster Candidate

    # of Dives: 1,000 - 2,499
    Location: Krung Thep, Siam, mostly.
    I’m kinda surprised that you bought a top-of-the-line 2nd stage but have paired it with a respectable but, IMHO, rental grade 1st stage. There’s alot of information on this board re the X650, which is usually paired with the MK25 1st stage, (early X650s had some problems when it first came out) if you do a search. Here’s one but there are many others:


    DA Aquamaster is the Scubapro expert on this board—you could also try to get his opinion by PM.
  3. dbg40

    dbg40 Solo Diver

    Agree, the MK2 is a bullit proof little unit, but not much to grow on. Newer 650's are a pretty good choice for a 2nd and paired with the superior MK25 can deliver impressive performance. But all in all you bought a quality set up im sure youll be happy with, and you can always move up to the 25 as time and $ permits. Congrats!
  4. halocline

    halocline Solo Diver

    I'm not sure you have the X650 2nd stage and the mk2 1st; if it's new, it doesn't make much sense that a dealer would pair those together. Since you're a new diver, what I would do is try to return the X650, if that's what you have, and get the R190 (maybe now it's R290) 2nd stage that usually pairs with the mk2 1st stage. It will be quite a bit less money. That combination (mk2/R190) gets labeled as a "rental reg" by gear heads, but it also has about the best track record of any regulator in history for reliability, and believe me, you'll never feel the difference given the type of diving you'll be doing for a while. Expensive, high performance regs deliver way more air than any human needs under virtually all circumstances.
  5. DA Aquamaster

    DA Aquamaster Directional Toast ScubaBoard Supporter

    # of Dives: 2,500 - 4,999
    Location: NC
    The Mk2 X650 combination is a little unusual. It's a bit like putting a $1000 stereo system in a $500 car.

    The Mk 2 has a flow rate of about 92 SCFM at a 3000 psi supply pressure and this falls off a bit at lower pressures. This is a little less than 1/3 the flow rate of the Mk 25 that the X650 is normally paired with. But it should be adequate for recreational diving at 130 ft or less under nomral conditions. Where the low flow rate can become problematic is in very high workload situations and with a panicky, air sucking OOA buddy at depth as in either situation it is possible to over breathe the first stage.

    With an unbalanced piston design like the Mk 2, the intermediate pressure falls as tank pressure decreases and this will be appraximately a 20 psi difference as the tank pressure decreases from 3000 top 300 psi. The Balanced X650 second stage will not be affected as much by this as an unbalanced R190 or R390 would be but there will still be a noticeable increase in inhalation effort as the pressure falls below 500 psi. This is actually a good thing as it sends you a pretty clear warning that you are almost out of air.

    First stages do not get any simpler, more reliable or more mechanically bullet proof than the Mk 2 and they are very easy to service so that is a definite plus. The TIS system, which is problematic in the Mk 25 in water colder than about 40 degrees, is more than adequate in the Mk 2 and the reg can be used reliably in water a cold as 32 degrees. So what it lacks in brute performance it makes up for in reliability.

    One suggestion though is to consider talking to the dealer about trading/upgrading your new Mk 2 Plus for a Mk 16 first stage as long as your regulator is still new and unused. The dealer cost for the Mk 16 is only about $25.00 more and the MSRP is only about $50 higher for the Mk 16 so for about $50 you could have a balanced first stage that delivers nearly twice as much air (177 SCFM). It would be a better match for the X650.

    The X650 is a very good second stage with an excellent poppet design. The only downside is that the potential of the poppet can not be fully utilized due to the case design and the location of the exhaust valve, something it has in common with the S600 and other conventionally designed second stages. If the poppet is adjusted by the technician for minimum breathing effort, (which is what the adjustment instructions I have do) air escaping out the upper edge of the exhaust valve will cause the poppet to open slightly and produce a very slight freeflow in the pauses between breaths. Many divers I suspect do not notice this nor find it annoying. If however you do find it annoying you have to increase the inhalation effort with the adjustment knob (which increases the spring pressure forcing the poppet against the orifice) until it no longer occurs and this results in an inhalation effort of nearly 2" of water.

    It is a better compromise if the tech adjusts the orifice to produce a cracking effort of 1.4 inches of water. This creates a couple millimeters of slack in the lever and prevents the poppet from opening as air escapes the exhaust valve to equalize the pressure in the case to the level of the exhaust valve.

    The X650 offers excellent flow rates and very smooth air delivery and would be well matched to a higher performance first stage like the Mk 16 or Mk 25 if you upgrade in the future. It is also very reliable in cold water and would make a very good cold water reg if paired with the Mk 16 which is itself a very reliable cold water first stage.
  6. Jafo123

    Jafo123 Solo Diver

    # of Dives: 50 - 99
    Location: Hinton,Iowa
    Like I said I'm not a tech. junky and after what some of you have said I'm not to sure it's not a MK25 1st stage. Still trying to make sence out of this manual.

  7. Moogyboy

    Moogyboy Contributor

    # of Dives: 25 - 49
    Location: Columbus, Ohio
    hey Jafo

    You can tell which first stage you have by its basic physical layout. I think the Mk16 and MK25 regs are right-angle designs while the Mk2 Plus is straight.


    Billy S.
  8. aquaoren

    aquaoren Contributor

    # of Dives:
    Location: Guelph, Ontario, Canada
    Pics? :wink:
  9. jonnythan

    jonnythan Knight Scublar ScubaBoard Supporter

    # of Dives: 200 - 499
    Location: Upstate NY
  10. Jafo123

    Jafo123 Solo Diver

    # of Dives: 50 - 99
    Location: Hinton,Iowa
    OK, as usual I shot off my mouth before I knew what I was talking about. It is a MK25. The dive shop showed me where to look and it is a right angle 1st stage.

    Thanks everyone for your replies. You did help.


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