Nature of Problem: Failure of BCD
Halfway out of Mayor’s Chamber of HERUC (Hinatuan’s Enchanted River Underwater Cave), my BCD suffered a leak through the purge valve. Four FCD’s use Hollis SMS 100 in the sidemount configuration. Out of convention, the power inflator and the purge valve were switched positions:
Figure 1, right shows the purge valve mechanism on the left shoulder. At first glance, this would not cause any problem. However, in the limestone dissolution cave environment, an unforeseen problem of pieces of limestone falling from above as they are dislodged by the bubbles in open circuit diving, proved to be problematic.
The Exit from HERUC and the Deco Stops
I literally had to crawl out of HERUC. As luck would have it, during the planned deco stops, Enchanted was current-neutral. (I have dived the area with a hefty down current at the height of the flood stage of a spring tide).
Problem Analysis
After an uneventful completion of the deco schedule, analysis revealed a small speck of limestone lodged under the purge valve lid causing the free-flow. The Hollis® SMS 100 is unprotected on the shoulder position. In the conventional configuration, it is well protected in the left hip area. Incidentally, the Hollis® SMS 50 purge valve is around the left shoulder area, but securely protected by the bladder.
Hindsight Solutions
Either one will do:
- Position the power inflator and purge valve in conventional manner – power inflator on the left shoulder, the purge valve tucked under the bladder in the left hip area
- Redundant bladder with independent power inflator
Article by:
Filipino Cave Divers 
FCD Andy likes his purge valve on the left shoulder. he is devising an add-on cap to prevent debris from falling into the purge valve mechanism.