Rigging for slinging a stage bottle
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PfcAJ
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I do know that a reg+shutoff without an OPV is a disaster waiting to happen.
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Poseidons do fail closed due to the upstream design. OPV's are 100% required if you have bottles that do not have a downstream second stage on them. BC hoses fail closed which is why some CCR's have OPV's on the bottles if all that is coming out of them are QD hoses and SPGS.
Shutoff valves are basically adding a QD in the reg hose. UTD did this for their sidemount system to swap 2nd stages around different bottles, stupid system for that, but the premise is the same. Shutoffs just create a local block in the air flow to prevent exactly what happened to dreamdive. Charge the system, turn the valve off, and all of a sudden the system becomes not charged due to either pressure, or the second stage purge button getting hit or a freeflow and now the reg is loose in the valve. This isn't as much of a problem for piston regs, but it can really screw with a diaphragm first stage. When you put this system in place, and a HP seat fails, the IP climbs and the air has nowhere to bleed off. So now the IP climbs past the rated service pressure of the LP hoses, usually around 250 psi *my poseidon branded hoses actually have a 500psi burst pressure, those suckers are never going to blow*, and because the metal is stronger than the rubber, the hose explodes, bad news because this hose leak can drain a full AL80 in a couple of minutes, scary stuff. 60cfm seems to ring a bell for some freeflowing second stages.
Some people like to put shutoffs on their stage bottles, I don't, but my O2 bottle has one, they are slowly being incorporated into deco bottles, and when I get more into rebreathers I'm sure they will find places there. Backgas will likely never have them though, I wouldn't worry about it too much.
Shutoff valves are basically adding a QD in the reg hose. UTD did this for their sidemount system to swap 2nd stages around different bottles, stupid system for that, but the premise is the same. Shutoffs just create a local block in the air flow to prevent exactly what happened to dreamdive. Charge the system, turn the valve off, and all of a sudden the system becomes not charged due to either pressure, or the second stage purge button getting hit or a freeflow and now the reg is loose in the valve. This isn't as much of a problem for piston regs, but it can really screw with a diaphragm first stage. When you put this system in place, and a HP seat fails, the IP climbs and the air has nowhere to bleed off. So now the IP climbs past the rated service pressure of the LP hoses, usually around 250 psi *my poseidon branded hoses actually have a 500psi burst pressure, those suckers are never going to blow*, and because the metal is stronger than the rubber, the hose explodes, bad news because this hose leak can drain a full AL80 in a couple of minutes, scary stuff. 60cfm seems to ring a bell for some freeflowing second stages.
Some people like to put shutoffs on their stage bottles, I don't, but my O2 bottle has one, they are slowly being incorporated into deco bottles, and when I get more into rebreathers I'm sure they will find places there. Backgas will likely never have them though, I wouldn't worry about it too much.
Curious why you decided not to put an OPV on the reg? I admit that if you're checking IP before you get in the water to ensure there's no creep the odds of it developing while on the dive are slim, but not zero. Does something about the OPV on the market concern you at 200m or is this just another arbitrary "failure point" argument?
kwinter
Contributor
Claudia - As much as it pains me, I have to agree with AJ. And of course with tbone. To insist that you don't need OPVs on the first stage is to deny the overpressure function of the second stage. Of course it doesn't matter if you don't have a problem with the first stage, but we plan for having problems. I guess I just don't understand what your objection (or Peter's) is to putting an OPV into the first stage. It doesn't change the profile or routing, costs less than $10, and could prevent a huge problem while having almost no possibility of adding a failure. Sure, I have had OPVs leak, but they are small leaks compared to the blown LP hose (which I have had as well). It is literally the ounce of prevention.
As to the first stage problem you described, I guess I don't really understand that one. But I do dive the same way that you described in turning all bailouts on to pressurize the second stages and then slide the shutoffs to the off position for the dive. Without the back pressure, the diaphragm could invert. But I always want every one of my offboard bottles turned on in case they are needed. Just one less thing to worry about.
Ken
As to the first stage problem you described, I guess I don't really understand that one. But I do dive the same way that you described in turning all bailouts on to pressurize the second stages and then slide the shutoffs to the off position for the dive. Without the back pressure, the diaphragm could invert. But I always want every one of my offboard bottles turned on in case they are needed. Just one less thing to worry about.
Ken
PfcAJ
Contributor
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