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SPGs on CCRs

Discussion in 'Rebreather Diving' started by doctormike, Apr 22, 2019.

What sort of tank pressure monitoring system do you use on your CCR?

  1. Stock SPGs, Front Mounted

    29 vote(s)
    55.8%
  2. Stock SPGs, Back Mounted

    6 vote(s)
    11.5%
  3. Wireless transmitters

    6 vote(s)
    11.5%
  4. Wireless transmitters and SPGs

    1 vote(s)
    1.9%
  5. Button SPGs

    5 vote(s)
    9.6%
  6. None

    4 vote(s)
    7.7%
  7. Other aftermarket SPGs

    1 vote(s)
    1.9%
  1. doctormike

    doctormike ScubaBoard Supporter Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: New York City
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    I just hijacked a FB thread in one of the JJ groups where someone was posting about their adapter for using a wireless transmitter and the original SPGs. I realized that while this discussion was interesting, it would be better here as a separate thread.

    I have heard experienced CCR divers say that they never check their tank pressure during a dive, so they just use button gauges. I have heard other divers say that they want to continually monitor their tank pressure through a dive computer. I'm interested in the arguments for different approaches. Here is what I posted. For those who haven't seen a JJ, the HP hoses are routed between the wing and the back mounted counterlungs, with the SPGs tucked in the back of the unit, in front of the valves, where they can be pulled out and then restowed. I didn't like the stock velcro hose keeper on the wing, so I rigged a small bungee loop on the backplate to keep them in place after pulling them out for a check.

    One of the nice things about the JJ is that it's so simple and clean, with minimal failure points. I really like having the SPGs routed where they are since they are out of the way. I don't see the point in putting two transmitters into the crowded space under the can, especially since they are more vulnerable than on an upright OC tank (CCR tanks occasionally slip down).

    Other than a boom drill (or a real boom), when do you guys check your gas during a dive? The SPGs are pretty easy to check in the very rare case that the information will change your failure management.

    Dil generally not an issue, but if you can't add dil and you check your tank valve and inline shutoff and they are open, then bail out or possibly plug in offboard if you are for some reason actually out of dil and you still need it. You are ascending anyway, unless you are in a cave with up and down exits.

    You can check your SPG if you have a boom and want to confirm O2 and stay on the loop for ascent. If you have actually run out of O2 without a boom, that's a planning problem. But if you can't maintain your PO2, it's either OOG, O2 tank valve shut, or some sort of downstream failure (e.g first stage). In any case, you need to plug in offboard O2, bail out or go to SCR mode, right?

    I know that more information is good, but since with SPGs you have the info in the rare case that you need it, why add cost, complexity and failure points? It's not like OC where you have a turn pressure that you need to watch for...
     
    KenGordon likes this.
  2. tbone1004

    tbone1004 ScubaBoard Supporter ScubaBoard Supporter

    # of Dives: I'm a Fish!
    Location: Greenville, South Carolina, United States
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    don't bother checking, never used them, even in training. Button gauges optional if you're diligent enough to put a pressure gauge on before the dive, but I'm far too lazy for that nonsense so mine have buttons.
    I don't see the benefit of them while diving either. O2, you either have enough, or you don't. If you don't, run SCR or bail out until you get back to a deco bottle and can plug in offboard. nbd. I don't believe in using the onboard 3l for dil, it's too small to breathe off of, so I use it for suit and wing inflation.
    Dil/bailout is all offboard and I have an inflator on there that I can plug in if I have to if the onboard 3l runs out for some reason
     
    doctormike likes this.
  3. macado

    macado PADI Pro

    # of Dives: 1,000 - 2,499
    Location: Boston, MA (mentally in Cozumel, MX)
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    I have both of my SPGs front mounted. I played around with moving them on my waist but ended up putting them back over the shoulders and down my harness. I understand the JJ ones are tucked away behind you and most people only check them during boom drills and such..

    Unlike a lot of people I do check my rebreather SPGs. Not as much as open circuit during the dive but I've run into situations on weird saw tooth profiles in caves/mines where I can effectively kill a 3L dil bottle during a dive. This doesn't happen very often but it's just one example. I could do what tbone1004 suggested and ultimately may end up doing that at some point but a large majority of my diving is not caves so I am happy running on-board for wreck diving.

    I also do multiple dives on the same set of bottles frequently. For example in Mexico I've done 3-4 dives a day on a set of 3L (and 2L) bottles. In these cases I like to know what I have left for onboard gas. And yes I know i can plug in off-board diluent as I ended up doing that in Mexico a few times.

    It may not be completely necessary but I like being able to quickly check my SPGs. You can use the SPGs to calculate "turn pressure" based on what you have left in your O2 or Dil. I maybe check my SPGs 2 or 3 times during a dive provided I don't run into any issues (leaks / boom drills). Not a whole lot but I like that information.

    I like simple things like hitting my MAV buttons and checking my valves are on and I still briefly look at my SPGs before I splash. Perhaps it's an old OC habit but I still like doing it.

    That being said, I have a love/hate relationship with SPGs, spindles, HP hoses. I hate jumping in the water only to see gas pissing out of my end of SPG because of the spool (spindle). If I could replace them with with HP transmitters while eliminating a failure point I would do it. For units like the X-CCR I really like that it has HP sensors built into the head and displays gas pressures on the Shearwarer via divecan.

    I don't think I would run SPGs and HP transmitters together specially if I had to add a splitters and still use an HP hose. It wouldn't really solve anything for me and would add more potential failure points. If I could just add transmitters to my first stages without the need for a spindle and HP hose then I would probably do it in the future. I'm willing to accept the risk of the transmitters occasionally dropping out.

    So like everything in the diving world..it depends. :)
     
    rjack321 and doctormike like this.
  4. Imla

    Imla Divemaster

    # of Dives: 500 - 999
    Location: Oslo, Norway
    625
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    63
    Was it "Sami-Someone"? :D

    Personally I dive a GUE setup so no transmitters here, but I could see his argument on the FB thread. (The JJ just works, so you need _one_ (or 8... I think he counted the extra o-rings) failure point to get a little bit to do between dives....
     
  5. doctormike

    doctormike ScubaBoard Supporter Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: New York City
    5,991
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    Yup, I posted the link to this thread in that one...

    :)
     
  6. The Chairman

    The Chairman Chairman of the Board

    # of Dives: I just don't log dives
    Location: Cave Country!
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    I dive an SF2, and have wireless on my side-mount bailouts and SPGs on my back-mounted O2 & dil. I plug into my LS bail out bottle, but I don't know that I check them very often during a dive. Maybe to marvel how much gas I have left. :D :D :D
     
  7. doctormike

    doctormike ScubaBoard Supporter Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: New York City
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    113
    Hah! That is a wonder, isn’t it....

    Why wireless on bailout? I mean, I do check that from time to time, but the SPG is right there...
     
  8. The Chairman

    The Chairman Chairman of the Board

    # of Dives: I just don't log dives
    Location: Cave Country!
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    I hate lollipops. I actually dive with 4 PDCs. Two Petrels, one CanBus the other a Fischer Cable, my Teric (for AI) and my Descent for it's GPS. Both the Teric and Descent are in gauge mode.
     
  9. doctormike

    doctormike ScubaBoard Supporter Staff Member ScubaBoard Supporter

    # of Dives: 1,000 - 2,499
    Location: New York City
    5,991
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    Maybe button gauge on your bailout? And I definitely love my NERD!
     
    Cyborg Pirate likes this.
  10. The Chairman

    The Chairman Chairman of the Board

    # of Dives: I just don't log dives
    Location: Cave Country!
    55,218
    22,324
    113
    Yeah, I can't afford one at the moment. It would eliminate two PDCs for me. I love having my dives geo-stamped with the Descent.
     

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