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David, As I have previously posted, I agree...keep the isolator open. There is, however, a flaw in your logic. It is called economics. It would not be cost effective to design and manufacture a different valve for the end post and the isolator. Since the valve was designed with the needs of the regulators in mind, there may be a lot of room for partial closure of the isolator without deleterious gas flow effects between the tanks. But I digress...keep it open!!! Lee David Pearson wrote: > This is a classic problem for configuration management. > > What is the purpose of the isolator? > - to isolate the tanks in the event of a failure where the offending side > valve cannot stop the loss of gas. > > Requirements for an isolator valve: > > Req. Precondition Requirements > ==== ============ ============ > 1 Open It must flow enough gas in a variety of diving conditions. > > 1.1 Open The "enough" gas state is affected by environmental > conditions including, but not limited to: > - Increased flow due to depth. > - Increased flow due to diver exercise. > - Changes in valve geometry due to temperature. > > 2 Closed It must flow no gas when isolating. > > 4 Both There must be a means of toggling from one state to the > next. > > 4.1 Open The transition from open to closed must be done so as to > minimize gas loss in the event of an emergency. > > 4.2 Both There must be a means of determining the status of the > isolator valve. > > 4.2.1 Open Based on requirements 4.2, 4, and 1, there must be a > means of determining that it is flowing "enough" gas. > > 4.2.2 Open Given the position of the valve (behind the diver's head), > the valve status determination must either be tactile or > through visible remote indicator. > > Assumption: > The valve manufacturer analyzed the gas flow requirements, and built the valve > to meet these requirements while in the fully open position (with a suitable > safety factor). > > Convolution in the making: > By partially closing the valve, you are removing the safety factor, potentially > below requirements. Partially closing the valve makes it difficult to comply > with 4.2.2 under all conditions listed in 1.1. You could add a second pressure > gauge to monitor disparity between the tanks. You could listen carefully for > the sound of gas flow. Both of these solutions add complexity. The partial > closing is an attempt to address 4.1 (minimize gas loss in an emergency). The > loss of gas issue can be dealt with in a number of ways (large volume, low > pressure tanks come to mind). > > Further analysis: > I have avoided the usability and reliability requirements thus far. There has > already been significant discussion around these topics. > > Conclusion: > Leave it open, practise closing it. > > Cheers > David Pearson > > In message "seeking opinions on isolator valves", cobber@ci*.co* writes: > > > Tony- > > > > IMHO I think that this isolator thing is something you can get fixated on > > while missing the big picture. I am trying to picture a scenario in ocean > > diving where you would need the isolator- > > > > - Your valve fell apart (avoidable by proper maintenance.) > > - You hit something so hard you snapped off your DIN and broke your valve > > wheel (avoidable by not diving off of waterfalls or improving your > > scooting technique.) > > - Your valve oring fails (this would be a slow leak, plenty of time.) > > - Your burst disk fails (double those bad-boys up.) > > > > Seems to me if you fuck with your valve so it can't open up all the way > > you might screw up PP fills as it would not let the gas moves as freely > > into both tanks. > > > > Jim > > > > On 3/29/98 3:19 PM Tony Phillips wrote: > > > > > Jim > > >Just a thought but it really wouldn't be difficult with many isolator > > >assemblies > > >to pack the valve stem so that it would only open say 2 or 3 (or whatever) > > >turns. > > >That way the valve could be "fully open" by feel but would be much faster > > >to shut > > >down. One would obviously need to make sure that in the full open position > > >the > > >gas flow would be adequate - say a little over half the requirement for a > > >diver > > >working hard since the diver. > > >Have been kicking this idea around for a while. Any comments? > > >Tony Phillips > > > > > > ------------------------------------------------------------------- > > Learn About Trimix At http://www.cisatlantic.com/trimix/trimix.html > > > > > > -- > > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. > > > -- > Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. > Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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