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Christalmighty, I haven't seen a post so nauseatingly detailed since Carl's trip report. Just what I need, more divots on my forehead. Why don't you just take this fucking scooter and shoot it, it needs to be put out of it's misery. Jim on 6/8/97 7:46 PM Richards wrote: > >Persuant to an interesting little episode with my loaner scooter, >the result of which Ken so gracefully mentioned; I have discovered >an interesting and insidious failure mode for the standard reed >switch which most of use have in our scooters. > >For those not in the loop: > >A reed switch is a small glass vial with two thin slits of metal >constructed into either end, one of which is pulled into the other >by a magnetic force, closing a circuit between the two exposed wire >ends. They are normally low voltage circuits, just strong enough to >trip a larger relay, which controls power to scooter motors. > > >In the typical Tekna or Oceanic version (and I expect the Gavins as well) >the reed switch is soldered to a wire on either side, and covered and >protected by heat shrink tubing. >------------------------------------------------------------------------ > >BEWARE: The reed switch vial will not withstand significant atmospheric >or hydrostatic pressure. Damage caused by either of these factors will most >likely crack and break the glass vial. Unfortunately, the heat shrink tubing >will temporarily hold the integrity of the vial, allowing the circuit to >operate normally, but totally shields the damage from even extremely close >examination. > >This in turn will allow the internal connections to corrode, and/ or cause >the >circuit to totally malfunction in the event of a sharp blow to the vehicle, >often >totally without any previous symptoms or indicators. > > >SUPPORTING EVIDENCE: I borrow a Tekna DV3X on a fairly regular basis, and am >the only operator of the vehicle. A few months ago, I took the vehicle to >Jackson Blue for a dive. I had improperly seated the main O-ring during a >pre-inspection the evening before, and as a result the vehicle flooded >immediately >upon intrance to the water. I did not notice this until i had reached 20 >feet, >where I dropped attempted to drop my Oxygen bottle. I immediately noticed >that the >scooter would not turn off, and aborting the dive, returned to the surface. >(The dive mission was completed on another vehicle.) > >On post-dive inspection I found that the entire vehicle had been flooded, >including the motor compartment (where the reed switches are housed) most >likely >due to the age of the scooter or poor previous maintenance. I immediately >drained >the entire vehicle and removed the bulkhead to allow it to dry, and to try >to determine >the extent of the damage. > >The following week, the scooter was reassembled, the motor compartment >checked to >see if it held a vacuum (it did, with no loss) and returned to service. >During the >reconstruction process, I took the time to check all the wires for excessive >resistance, >which, thought it is a poor indicator of wire health, would immediately show >breaks in the >wires beneath the sheath, which would not be indicated on visual >inspections. The reed switches, >when closed, showed no resistance (measurable with a low grade ohmmeter.) > >The scooter was then dove at Ginnie Springs and surrounding caves a number >of times. >No subsequent flooding was experienced, and the vehicle was inspected each >and every dive. >However, I did experience sporadic problems with the trigger mechanism, >occasional sticking, >or what I thought was sticking, and failure to activate. Each incidence was >independent, >non-related to depth, and never consistant in either duration of effect or >rate of occurance. > >Each time the scooter trigger mechanism was inspected for cable/pulley >fouls, sticking >magnetic slider, and broken trigger assembly. None were indicated. I took to >diving with >the cable cover plate removed, so that i could observe the magnetic slider, >and manually >operate it if need be. Periodically a sharp strike to the scooter body would >restart or >stop the scooter, but this was not always the case. > >Following Our dive last Thursday, I once again totally dismantled the >scooter, once having >reduced the problem to loose wires, the relay, or the reed switch. >Continuity was once again >checked throughout the system, and this time the reed switch failed to close >a circuit. >(The last failure was an open circuit; the scooter would not turn on.) I >removed >the switch, and carefully removed the shrink wrap tubing. To my suprise, >shards of the >switch came with it. The connections had been corroded, despite the good >installation of >the tubing. There was no previous indication of switch damage, either >electrical or visual. > >CONCLUSIONS: > >The partial failure of my single reed switch caused sporadic trigger/motor >control. >The eventual complete failure of the reed switch stranded me 3000+ feet into >the cave. > I believe that it could have just as easily failed in the closed >position, > causing a much more dangerous situation. >The only possible failure modes that I am aware of are submersion to 20 FFW >or old age. >The Protective cover presented me from noticing the damage upon visual >inspection. >The failure was not initially electrically indicated. > >I believe that in my case, the submersion of the switch to 20 FFW caused the >initial >damage to the switch housing, which might have been assisted by the physical >age of the >housing (I doubt it). The protective shrink wrap, which I feel is necessary >to expose >the bare wire connections, prevented me from noticing the damage, a >potentially dangerous >but unavoidable situation. > >SOLUTION: > >Reed switches are cheap. I bought two more for $2.65 each. They require a >little soldering, >a volt/ohmmeter and less dexterity than it takes to type to these lists to >install. > >If you have flooded your motor compartment, or continually sustain minor >leaks (i.e. the >housing leaks enough to equalize the internal/external pressure) I suggest >that you overhaul >your switches/send them to Barry for closer inspection/replacement. > > >Does anyone have any more on this? Bill Gavin? > >Thanks. > > Jason Richards > NSS/CDS 41539 > rchrds@ga*.ne* > > > -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send list subscription requests to `techdiver-request@aquanaut.com'.
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