[PSUBS-MAILIST] Hatch interlock

Wed Mar 2 07:41:51 EST 2016

Doing some further design on my lockout submersible project, I came up with a novel way to implement hatch interlocks, which doubles as a seal condition monitor, and a means of establishing a preliminary seal in the absence of a pressure differential without relying on the hatch dogs to provide the initial o-ring squeeze.

My design entails two o-rings per hatch (vessel has six hatches: cabin loading / escape, outer lockout loading / escape, inner lockout loading / escape, inner lockout egress , outer lockout egress, and transfer). These o-rings are concentric face seals, each residing within a half dovetail groove for positive retention of each o-ring when the hatch is opened or manipulated. The grooves are oriented such that the flat face of each half dovetail faces the intermediate space between the two rings. This intermediate volume is not isolated, but rather connected (on the sealing flange side) to a vacuum transducer, and piped through appropriate valving to a vacuum pump. When the hatch is closed, this intermediate space is pulled to vacuum (as strongly as the pump allows), then locked off, and the strength of this vacuum is measured by the transducer and continuously monitored. The interlock is clear as long as the vacuum holds, and activates the moment the seal is released, instead of
relying on some arbitrary movement of the hatch to indicate that it is open.

Apart from the obvious expense, I see a potential problem with exposing those vacuum transducers in the lockout hatches to high pressure, necessitating either a less sensitive transducer that will withstand the pressure, or some means of isolating the transducer when the pressure approaches the limit of its range - I'm still working this out in my head, but I thought I would share anyway.

Sean
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