returned to its original dimensions and no difficulty was encountered in 

 removing the end closure. Upon examination of the 0-rings, it was found 

 that they were ready to be used again as a seal. The design and fabrication 

 of the self-energized 0-ring seal in the elastic follower ring is rather simple. 

 These three elements are required: 



(a) Two 0-rings. One 0-ring under radial and one under axial compres- 

 sion are required. The elastic follower ring must be so dimensioned that the 

 0-rings are under sufficient compression at zero internal pressure to constitute 

 a low-pressure radial and axial 0-ring seal. The radially compressed 0-ring 

 must seal the inevitable small clearance between the vessel wall and the 

 external radius of the elastic follower ring, while the axially compressed 

 0-ring seals the clearance between the bottom of the vessel end closure and 

 the top of the elastic follower ring. The radial 0-ring is compressed at zero 

 hydrostatic pressure by the close fit between the exterior surface of the elastic 

 follower ring and the interior surface of the pressure vessel. The axial 0-ring 



is compressed at zero pressure by bolts pushing a retainer ring against the 

 elastic follower ring. When the pressure is raised inside the pressure vessel, it 

 acts axially and radially upon the elastic follower causing it to push harder 

 against the end closure and the cylinder, thus achieving zero clearance between 

 the follower ring and the seal surfaces. 



(b) An elastic follower ring. A ring sufficiently elastic to expand 

 across the gap between the head and the vessel and subsequently to follow 

 the radially dilating pressure vessel is required. For this application, the 

 follower ring must be less stiff than the vessel wall whose dilating it is following. 

 This is accomplished by making the follower ring either from material with a 

 very low modulus of elasticity or by making it from the same material as the 

 pressure vessel wall, but considerably thinner. Regardless of what material 



the follower ring is made, it must not yield during its radial dilation, or deform 

 due to shearing stresses imposed on it while it is bridging the gap between the 

 vessel end closure and the wall of the vessel. If either one occurred, the follower 

 ring would have to be replaced after each pressurization, making this type 

 seal uneconomical. 



To provide sufficient radial and axial forces on the follower ring to 

 maintain zero clearance between the ring and the seal surfaces on the end 

 closure, the 0-ring grooves (Figure B-7) must be machined at such locations 

 in the follower ring that hydrostatic pressure causes radial and axial movement 

 of the follower ring. 



71 



