F = Total force > — ^y*" = Direction of force 



a = Unit stress ^a) = Type of stress (compression, tension) 



Note: Se<f-energizing seal worl<s only when 

 g)>Qand@>Q 



resulting in radial dilation of elastic 

 follower ring and compression 

 and (oo j' "vhere (o/\ > (a 

 because of ring's resistance to3ilation. 



radial dilation 

 of vessel under 

 pressure 



Figure B-7. Forces acting on the elastic follower ring containing the radial 

 and axial 0-rings. 



(c) Radial precompression. The only shortcoming of the self-energized 

 radial seal is its requirement for sufficiently close (0.010 to < 0.020 inch) radial 

 fit between the external radius of the follower ring and of the interior surface 

 of the vessel to provide the initial compression of the radial 0-ring so that it 

 seals at low pressure and thus permits the self-energizing mechanism to function 

 with increase in internal pressure. In its requirement for close radial fit, this 

 seal is no different from the other seals investigated experimentally in this study. 

 It appears, however, that modifying this design (Figure B-8) may permit greater 

 clearance between the external radius of the follower ring and the vessel wall 

 at zero pressure. Such a development would, of course, ( 1 ) make the fabrication 



72 



