Appendix A 

 INVESTIGATION OF A VIEWPORT SEAL DESIGN 



INTRODUCTION 



A necessary, although oftentimes neglected, function of a viewport 

 design is that of maintaining waterproof integrity at all times. Even very 

 small leaks would be detrimental in a habitat (long term submergence) 

 because of the large accumulation over a long length of time, not to mention 

 the psychological effects on the occupants. Waterproof integrity is accom- 

 plished by a viewport seal system which must function in two environments: 

 (1 ) at the surface both before and after dives (low pressure), and (2) at the 

 operating depth (high pressure). 



The objective of this appendix is to (1 ) review and evaluate existing 

 methods of sealing submersible (short term submergence) viewports, but 

 with regard to the additional habitat functional requirements, and (2) 

 investigate both experimentally and analytically the most promising of the 

 designs. 



BACKGROUND 



To provide waterproof integrity, the first viewport seal designs 

 relied on a lapped-joint seal between the viewport and flange as shown in 

 Figure A-la. Achievement of the seal is by 80 to 90% contact surface area, 

 which requires surface finishes in the 8 to 32 rms range. This design main- 

 tained a seal at the lapped joint for both low-pressure and high-pressure 

 sealing. Sometimes a flat gasket is used for padding between the retainer 

 ring and viewport. 



The next design was the gasket seal as shown in Figure A-1 b. This 

 particular design relied on a gasket located at the perimeter of the high- 

 pressure face for low-pressure sealing and on the lapped joint for high-pressure 

 sealing. 



A similar design, as shown in Figure A-lc, had an 0-ring located at 

 the corner of the viewport high-pressure face. Here again the low-pressure 

 sealing was accomplished by theO-ring and the high-pressure sealing by the 

 lapped joint. 



The design shown in Figure A-ld is currently being used for 

 submersibles. Here both high-pressure and low-pressure sealing is accom- 

 plished by theO-ring seal. 



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