end-closure skirt and the vessel wall. However, when the internal pressure 

 approaches 10,000 psi, this plastic wedge, like the preceding seal type, 

 plastically extrudes and releases compressed water (Figure B-5). 



This seal represents a marked improvement over the preceding seal 

 type, as with this type no sealing difficulties are encountered at low pressures, 

 and it is only in the 5,000-to-10,000-psi range that this seal fails by extruding. 

 Both these seal arrangements have an unlimited capability to follow axial 

 displacement of the end closure, but only very limited capability to follow 

 the vessel's radial dilation. Both seal arrangements should have a plastic 

 rather than a metallic continuous wedge ring as otherwise the seals will not 

 follow the radially dilating vessel wall with sufficient compliance to assure 

 a continuous seal. 



0-Ring Seal With Split Antiextrusion Wedge Ring 



This seal arrangement is basically the same as that of the preceding 

 seal except that a split metallic ring has been substituted for the plastic contin- 

 uous ring. With this arrangement, the 0-ring seals well at zero and low pressures, 

 while at high pressures the metallic wedge ring is much more difficult to extrude 

 than the plastic wedge ring described above. However, if the clearance between 

 the end-closure skirt and the vessel wall became of the same magnitude as the 

 width of the wedge, it would be forced into that space by the hydrostatic 

 forces acting on the 0-ring. Once the metallic wedge was lost into the space 

 between the vessel wall and the end-closure skirt, it would cause the end closure 

 to jam and might prevent the removal of the end closure. 



This seal arrangement, like the preceding seal arrangements, can follow 

 any axial displacement of the end closure. It has only limited ability to follow 

 the radial dilation of the vessel, and the magnitude of radial dilation of the 

 vessel that this seal can compensate for is determined by the width of the split 

 metallic antiextrusion ring. 



Although this seal arrangement has overcome the shortcoming of the 

 first seal of not sealing properly at zero internal pressure, and the shortcoming 

 of the second seal of not sealing at pressures in the 5,000-to-10,000-psi range, 

 it had not overcome the single shortcoming common to ail; incapability to 

 compensate for large radial dilation of the vessel wall. Thus another seal arrange- 

 ment was conceived with the objective to seal well at zero pressure, at high 

 pressure of any magnitude, and to follow axial displacement of the end closure 

 and any magnitude of radial dilation of the vessel wall. Furthermore, to make 

 the seal installation simple and inexpensive, it was to utilize only commercially 

 readily available 0-rings and a minimum of custom machined parts. 



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