Distribution block question.....

Discussion in 'Sidemount Diving' started by Mitchell Teeters, Feb 21, 2012.

  1. Mitchell Teeters

    Mitchell Teeters ScubaBoard Supporter ScubaBoard Supporter

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    I'm eventually going to dive side mount and I have a question about the distribution block system. Since I will be using the block which will essentially equalize the pressure between the tanks, do I need two SPGs attached to each tank? I think one will suffice unless I'm totally wrong. TIA.
     
  2. ianr33

    ianr33 Orca

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    Distribution block??
     
  3. TSandM

    TSandM Missed and loved by many.

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    I'm assuming he means the Z-system that UTD makes. Do they have a port off the block for a HP hose? I think the block is just an LP distribution system.
     
  4. Mitchell Teeters

    Mitchell Teeters ScubaBoard Supporter ScubaBoard Supporter

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    Yes it is only LP, I was wondering if there would be equalization between the two, thus only one SPG. If this would work it would greatly simplify gas management.
     
  5. Teller

    Teller Scuba Instructor

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    Gas managment is already simple.
     
  6. TSandM

    TSandM Missed and loved by many.

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    You're not thinking it through. There's no place on the block to take a HP feed from. So you'd put one SPG on one of your tanks, and nothing on the other? How will you know when to swap tanks? (Because the block is a passive conduit, you have to run your tanks just like any other sidemount diver, running one open and the other closed, and then switching -- this is because any IP mismatch between the two tanks would result in you preferentially draining one, if you didn't use that technique.)
     
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  7. Mitchell Teeters

    Mitchell Teeters ScubaBoard Supporter ScubaBoard Supporter

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    That is why I'm asking. I would think that as one bottle donates air the other would also to equalize. If they equalize then the PSI would be the same in both tanks. I would think any differential would be minor. If you are drawing from a central location both would draw. I dunno. I've tried to glean out the z mount system.
     
  8. TSandM

    TSandM Missed and loved by many.

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    The problem with the block is that, as you inhale and lower the pressure in the system, the side with the higher IP will open first and refill the system. The first stage on the side with the lower IP will never open at all, so you will be drawing all the gas from one tank. For that reason, the Z-system is dived the same way as a standard sidemount setup -- when you are breathing off one tank, the other is kept closed.

    It's not like a transfill whip, where the two tanks equalize, because both tanks have first stages on them. With a whip, there is no first stage, but just a passive connection between the two gas sources, so pressures will equalize. Does that make sense?
     
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  9. DaleC

    DaleC Great White

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    Lynne is correct about the IP's. The lower IP side will not open until the high IP side reaches the lower IP. It won't transfill like you think.
    You have two tanks, both with their own first stage. From the first stage of each tank a LP whip runs to the gas block. From the gas block you run your reg and DS/BC whips. The LP air at the block would have to move through a higher pressure gradient to make its way from one tank to the other. Which it won't.

    When you transfill, you use HP-HP pathways, not HP-LP-HP pathways.

    With one SPG on the higher IP tank you will get an accurate read of that tank till it nearly empty, then you dive the second tank blind.
    With one SPG on the lower IP tank your gauge will read full until the higher IP tank is drained and then it will work for the second half of the dive.

    I tried this for a project linking multiple tanks and worked through the same thinking you are having with a group. Here I have two tanks connected at one first stage but I also tried it with a gas block like the Z system as well. It was fun but, like the Z system, it violated the KISS principle too much for my liking.

    robosock036.jpg

    Just food for thought: You could use one SPG if you connected two tanks using a transfill whip and DIN fittings: from a single post on tank A to post one of an H valve on tank B. Your traditional reg set goes on post two of the H valve.

    I wouldn't recommend it but it would work.
     
    Last edited: Feb 22, 2012
  10. nwbrewer

    nwbrewer Barracuda

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    I've seen this a few times and I don't get it.

    My level of experience in SM is admittedly very small, as is the number of SM divers I've actually dove with, but I'm not aware of a good reason in traditional SM to turn on/off your tanks when switching regs. It seems that if something goes wrong with the tank I'm breathing from, or I'm in a mixed team and need to donate, I don't want to be screwing around trying to get the other tank turned on.

    Somebody more experienced, help me out, do you really do this? If so, why?

    Jake
     
  11. Mitchell Teeters

    Mitchell Teeters ScubaBoard Supporter ScubaBoard Supporter

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    So if I were to run HP to HP on the first stages and have an extra HP port for a SPG I'd have a good reading. The reason I want to use the distribution manifold is to reduce the task loading while diving. Not needing to manage the valves and when to switch is what I'm trying to do. Simplify.

    The KISS mindset with managing two valves, locations of regs, stowage of hoses, etc, is that REALLY KISS? Versus set up one whip hose between two first stages, one SPG, never having to switch between tanks, just worry about your traditional primary and octo set up coming off your back is what I'm going for.
     
  12. amascuba

    amascuba Scuba Instructor

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    Yes, you will need a spg on both tanks. The system doesnt equalize the pressure from both tanks. If you turned both tanks on and breathed them down, the first stage with the more sensitive pressure seat will drain first. it's unadvisable to dive the system that way. It's quirky and is npt going to work like you think it is. therefore, id suggest getting trained on that specific system before you use it.
     
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  13. DaleC

    DaleC Great White

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    Remember I said I wouldn't recommend it and probably no one doing cave or technical dives would dive with you either. My project was for an open water vintage rig. One blown hose and you would loose all your gas. Either you isolate tanks in some way to provide redundancy or you dive one big tank. Perhaps someone who dives a Z system can tell us what happens if you blow one of the feeding LP whips to the block.

    Take your time. If that degree of task loading is daunting one shouldn't be using the technique. When it's time, the task loading won't be an issue. You should be comfortable doing reg swaps (what about using stage/deco bottles) it's a bonus when it comes to donating a reg and monitoring gas is not that hard when the SPG's are right in your face.

    Before spending all that money on a very unique rig that can't be used for anything else, get comfortable in the water with your basic skills and then seek out a mentor or instructor that will let you use a more traditional SM rig. You may find it's not that big a problem.

    I wonder if the Z system delivers what it promises. Most SM divers are going to wonder what the heck you are doing and, while the reg position is similar, BM divers are going to be confused by the equipment configuration and not feel it's standardized within the team. I dunno, perhaps a team could comment on that one.
     
  14. amascuba

    amascuba Scuba Instructor

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    Running hp to hp on the first stages will not work either. you're not grasping how the first stages work. The UTD z system only allows you to breath the same second stage, while still managing the gas in both tanks by turming on off and the other on. It's only advantage is having the same procedures for donating to an out of gas diver while diving in a mixed team environment. it does not equalize or simplify gas management of the side mount diver. It's still the same procedure, minus having to swap the second stage. If you plan on solo divong, the havimg a completely separate system still makes more sense.


     
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  15. amascuba

    amascuba Scuba Instructor

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    It's a misconception that with the z system that you will lose all your gas in the event of gas failure. You dive it with one tank turned off and swap based upon your current side mount gas management strategies. If a o-ring were to fail anywhere on the system, you have the capability of isolating the problem and continuing. If the o-ring is on the manifold, you disconnect the tanks and either breath from a second stage directly attached to the second stage that is tucked under bands on the tank, or you connect a spare second stage to the qc6 that is connected to the manifold.



     
  16. Slamfire

    Slamfire Loggerhead Turtle

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    I do transfill and equalize my tanks by running hp to hp on the first stages all the time. It is effectively my transfill whip. In that sense it does work very well actually. I have never done it underwater while diving and do not intend to do so. I would not feel safe doing so under water and have no need to do so. I would NOT recommend it to anybody as a way to equalize sidemounted double while diving. It is not robust enough to be dive worthy and you just set up to very easily lose the gas supply of both tanks. You effectively kill redundancy. I personally think it would be a bad idea.
     
  17. tech_diver

    tech_diver Equipment Manufacturer

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    I seem to recall that someone once sold a 'soft' manifold system where a braided HP hose allowed the two tanks to communicate. I did a quick google and couldn't turn it up. It might be interesting to hear from someone who used one.

    Also, most HP ports have flow restrictors such that they may not equalize as fast as they are breathed. This may or may not have an impact in real diving.
     
  18. Slamfire

    Slamfire Loggerhead Turtle

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    Good point. HP to HP transfilling can be much slower when compared to using a traditional transfill whip. It's not really a concern when transfilling; in fact I see as an advantage when dealing with high O2 mixes -- you just can't fill too fast. Still have to be careful to open valves slooowly, though.
     
  19. TSandM

    TSandM Missed and loved by many.

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    You know, I think I misspoke . . . I'm not a sidemount diver. Trying to remember diving sidemount with Rob, I don't recall turning the tank off when I switched regs. But you DO have to do it with the Z-system, because of the IP mismatch problem.

    If you blow a connection or hose downstream of the block on the Z-system, you have to disconnect both QDs, and then either breathe a regulator which has been bungied to your tank like a deco reg is, or pull a spare second stage out of your pocket and stick it on one of the QD hoses. Andrew doesn't think this is a problem, but I can't see myself getting that done expeditiously in the middle of a restriction somewhere.
     
  20. Mitchell Teeters

    Mitchell Teeters ScubaBoard Supporter ScubaBoard Supporter

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    So I would need to run a spare reg on both sides or have a QD attached so that I can change out the reg to the good side. Did I get that right?
     

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