Relationship Between Critical Pressure and Sealing Technique 



The evaluation of window sealing methods was conducted with a total of 

 20 windows (10 untested windows in addition to the 10 already tested in the evalua- 

 tion of Dq/D; ratio study). Five of the additional windows had a 1.33 Dq/D; ratio 

 and a 0.5 t/Dj ratio and a Dq of 2 inches (Figure A-3b), while the five others had 

 a 2.67 Dq/D; ratio and a 0.5 t/Dj ratio with a Dq of 4 inches (Figure A-3d). All 

 10 windows had a nominal l/8-inch-diameter radial O-ring seal located in a groove 

 machined in the window 0.125 inch below its high-pressure face. 



When the windows were tested to destruction in appropriate flanges (Figures A-la 

 and A-lc), the critical pressures of the O-ring-equipped acrylic flat windows were 

 19,060 (Table C-2) and 19,270 psi (Table C-17) — reasonably close to the pressures 

 (18,490 and 19,190 psi. Tables C-1 and C-16) of the corresponding windows sealed 

 in the flange with silicone grease. The displacements of the O-ring-equipped win- 

 dows were approximately the same as the displacements of grease-sealed windows 

 with the identical Dq/Dj and t/D; ratios (Table A-1). 



Thus, both seal designs are of equal desirability, so long as the sole criterion 

 for their selection is their influence on the critical pressure of the flat acrylic window. 

 For the main body of the flat window study program, where the relationship between 

 the t/Dj ratio and critical pressure is investigated, the grease-seal design was selected. 

 This design permitted the investigation of very thin, flat windows into whose body an 

 O-ring seal could not be incorporated. 



Relationship Between Critical Pressure and Window Fit 



Evaluation of the effect on critical pressure of radial clearance between the 

 flat acrylic window and the steel flange was conducted with a total of 25 windows 

 (5 untested windows in addition to the 20 tested in previous tests). The radial clear- 

 ance between the acrylic window and its flange varied from one group of window 

 specimens to another. One group of 10 windows tested previously had a radial 

 clearance of 0.001 inch (Figures A-3b and A-3d); another previously tested group 

 of 10 had a clearance of 0.025 inch (Figures A-3a and A-3c). The group of 5 win- 

 dows tested in addition to the 20 windows tested previously had a radial clearance 

 of 0.150 inch (Figure A-3a). Appropriate flanges (Figures A-la, A-lb, and A-lc) 

 were used with the windows to result in 0.001 -inch, 0.025-inch, and 0.150-inch 

 clearances. 



When the critical pressures of all the window groups were compared to each 

 other, no significant difference in critical pressures could be found between the groups 

 of windows possessing radial clearances of 0.001 inch and 0.025 inch, respectively. 

 There was, however, a significant difference between the 16,960-psi (Table C-3) 

 critical pressures of the window group with a radial clearance of 0.150 inch and the 



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