Isolator Valve Loosy-Goosy?

[coldsmoke]

Just checked mine - it will turn but not all the way around and not real easy. In fact I would be kind of concerned to rotate too much. It doesn't move easy.
HP 100's @ 2000 psi, DR manifold.

Does that mean that my bands are too tight or that Ricks are too loose? Or what else is making ours rotate differently? Same manifold, same pressure - what gives?

Hunter

 

[Rick Inman]

Just checked mine - it will turn but not all the way around and not real easy. In fact I would be kind of concerned to rotate too much. It doesn't move easy.
HP 100's @ 2000 psi, DR manifold.

Does that mean that my bands are too tight or that Ricks are too loose? Or what else is making ours rotate differently? Same manifold, same pressure - what gives?

Hunter

FYI, mine will not turn but a bit forward, but get easier as they go back around.

 

[JeffG]

Just checked mine - it will turn but not all the way around and not real easy. In fact I would be kind of concerned to rotate too much. It doesn't move easy.
HP 100's @ 2000 psi, DR manifold.

Does that mean that my bands are too tight or that Ricks are too loose? Or what else is making ours rotate differently? Same manifold, same pressure - what gives?

Hunter

Sounds about right. Mine can only move maybe 1/2 of a turn.

 

[Jay Roy]

None of the doubles I've gotten from Zero Gravity even have the lock nuts on.....

How parrallel the tanks are will greatly impact how much the isolator can turn freely..The threads on the isolator bar are pretty fine and the tanks wouldnt have to be out by much to cause the threads to bind...

 

[DA Aquamaster]

Help me understand the tradeoff involved...because frankly I don't get it.

If you bump the isolator you could potentially break it. More precisely unless you beat the living hell out of it you run the risk of "only" breaking the knob and rendering the isolator valve unable to be closed. (And if you then need to use the isolator valve you've by definition had a multiple failure and that is beyond the scope of most redundancy planning.)

The risk of breaking a rubber knob is a lot less than a plastic one and unless you are using a metal knob, bending or breaking the stem on the isolator is very unlikely.

On the other hand, even though you have a barrel type assembly with two o-rings per side, they were never intended to be dynamic o-rings. They are also only marginally what I would consder to be "fully captured" as by definition the male and female parts of the connection have to have some play between them to turn at all and in particular to turn when less than perfectly aligned - as occurs during assembly.

So in effect, you are placing a great deal of faith already in the o-rings even in a static condition and obviously they are in redundant pairs for good reason. And for equally good reason, the crossbar comes with lock nuts to ensure that the o-rings and cross bar do not experience wear due to dynamic movement under pressure.

In light of the mechanical realities of the design, why would anyone choose to leave the isolator cross bar lock nuts loose (or off) and in turn ensure the isolator will move back and forth slightly increasing wear on the o-rings as well as increasing wear on the cross bar and mating surfaces on each post? It strikes me as a case of the long term effects of the vacination of the disease being far worse than what is at worst a very rare and often non fatal disease that you can only catch by being stupid in the first place (ie: you have to have a broken isolator and a tank burst disc or a reg failure at the same time as the broken isolator for it to be a problem on a dive and to accomplish that you have to hit something incredibly hard).

 

[PfcAJ]

I've had a few discussions about this with some GUE divers/instructors, as well as some personal experience.

A while ago, I pulled away from a fill station with my 104s in the back of my truck. Suprise! The tailgate dropped...along with the tanks. At 15mph, the tanks landed manifold first onto asphault.

No leaks. 1 knobs was sheared off and the crossbar looked like a shallow S, once valve face was deformed. The only thing that emptied was my wallet, the tanks did not leak at all.

The O-rings in a manifold are designed to be static, not dynamic. Frequent movement could (and probably does) cause unneeded wear on those O-rings, which could fail in time. For the most part, we keep the manifold locked in place.

With a slight forward angle on the isolator, it is well protected. Of course, things can happen, but thats why we have buddies and solid gas planning to account for a massive blunder. Oh, and try not to smash into the celing...

 

[Rick Inman]

Help me understand the tradeoff involved...because frankly I don't get it.

If you bump the isolator you could potentially break it. More precisely unless you beat the living hell out of it you run the risk of "only" breaking the knob and rendering the isolator valve unable to be closed. (And if you then need to use the isolator valve you've by definition had a multiple failure and that is beyond the scope of most redundancy planning.)

The risk of breaking a rubber knob is a lot less than a plastic one and unless you are using a metal knob, bending or breaking the stem on the isolator is very unlikely.

On the other hand, even though you have a barrel type assembly with two o-rings per side, they were never intended to be dynamic o-rings. They are also only marginally what I would consder to be "fully captured" as by definition the male and female parts of the connection have to have some play between them to turn at all and in particular to turn when less than perfectly aligned - as occurs during assembly.

So in effect, you are placing a great deal of faith already in the o-rings even in a static condition and obviously they are in redundant pairs for good reason. And for equally good reason, the crossbar comes with lock nuts to ensure that the o-rings and cross bar do not experience wear due to dynamic movement under pressure.

In light of the mechanical realities of the design, why would anyone choose to leave the isolator cross bar lock nuts loose (or off) and in turn ensure the isolator will move back and forth slightly increasing wear on the o-rings as well as increasing wear on the cross bar and mating surfaces on each post? It strikes me as a case of the long term effects of the vacination of the disease being far worse than what is at worst a very rare and often non fatal disease that you can only catch by being stupid in the first place (ie: you have to have a broken isolator and a tank burst disc or a reg failure at the same time as the broken isolator for it to be a problem on a dive and to accomplish that you have to hit something incredibly hard).

Everything you just said is what my I was discussing wth my dive buddy today.

Which is why I asked the question.... ??

 

[rainman_02]

If you're replacing the o-rings once a year...is the wear and tear really that much?

 

[MonkSeal]

If you're replacing the o-rings once a year...is the wear and tear really that much?

I guess this is sufficient. Once I replaced these o-rings after two years and could notice wear and tear marks.

 

[DA Aquamaster]

Whether the replacement interval is sufficient depends on how much you dive and how much the isolator gets rotated as well as salt contamination, silt, and a bunch of other aggravating factors. If you do half a dozen dives in a crystal clear cave systyem per year the challenges are a lot less than if you do a 100 dives per year in seawater or silty conditions. Annual replacement also does not change the fact that a loose isolator places the o-rings and crossbar outside of the intended design parameters. It was simply never intended to rotate under pressure.

My thoughts are that if you replace the o-rings after 2 years and noted wear and tear, there was a degree of wear and tear at the one year mark. Its probably not a linear relationship, but how much wear does a diver find acceptable compared to the the minimal wear that occurs when the isolator is tighted as intended?

Again the question is why would anyone willingly accept dynamic wear and tear on a static o-ring that poses a genuine threat of gas loss in order to reduce the potential to break an isolator valve that is extremely unlikely to ever occur in the first place and is unlikely to cause gas loss in and of itself. If it does break, it would only have the effect of converting your isolator crossbar to a regular crossbar that would not be problematic on the dive unless you had an additonal failure that could not be resolved by shutting down either post.

In my opinion, a loose isolator is one of those things that sounds like a good idea until you really think about it, compare the pros and cons and weigh the risks of doing it versus not doing it.

Personally, I am not into adding a known degenerative condition to a system in order to alleviate a potential risk that is exceedingly rare and preventable by other means that do not degrade the system.