GB1097582A - Closure mechanism for pressure vessels - Google Patents

Abstract

1,097,582. Reactor pressure vessels. GEARTIGHT UNIONS Ltd. July 6, 1964 [April 4, 1963], No. 13500/63. Heading G6C [Also in Division F2] A self-locking closure plug for a pressure vessel, particularly for sealing nuclear reactor standpipes, comprises a lower annular portion 2 and an upper annular portion 3 capable of a limited degree of relative axial movement, the upper portion 3 carrying around its periphery a number of equi-angularly disposed cam members 4 which can swing in radial planes and have lower cam lobes 5 shaped for engagement in a locking recess 6 in the wall of the opening to be closed, e.g. the opening at the top of a standpipe 1. The upper portion 3 is of composite form and comprises a ring 7 and a radially outwardly extending flange 8 in which are formed equi-angularly spaced peripheral recesses 9 for supporting the cam members 4. The cam members 4 are located in the recesses 9 by a sleeve 11 having at its upper edge a radially inwardly extending annular flange 12. Bolts 13 extend freely through the flanges 8, 12 and the lower portion 2 and are screw-threaded into a member 15 which has a compression-type sealing ring 17 held in a recess 16 by a ring 18. Axial movement of the lower portion 2 and the member 15 towards and away from each other is effected by a shank 21 having a small pitch square section thread which engages with a thread on the internal wall of the lower portion 2 and terminating in a radially outwardly extending flange 22 which extends into a recess 23 in the member 15, a bearing surface 24 being disposed between the flange 22 and the floor of the recess 23. At its upper end the shank 21 terminates in a head 25 shaped for co-operation with a hollow driving shaft (Fig. 2, not shown) by which the shank 21 can be rotated. Before fitting the closure plug to the standpipe 1, the shank 21 is first rotated so that the lower portion 2 and the member 15 abut each other, as shown in Fig. 1. The plug is then suspended from a raising and lowering mechanism (not shown) which co-operates with the shaped internal surface of the ring 7. Due to gravity the ring 7 slides up the bolts 13 so that the flanges 8, 12 abut each other, the stepped lower surfaces 5b of the cam lobes 5 ride up the sloping surface of the lower portion 2 out of engagement with a complementary abutment surface on the portion 2, and the cam lobes 5 retract and do not project beyond the sleeve 11. The plug is then lowered into the opening of the standpipe 1 until the sealing ring 17 engages with a shoulder 20 on the wall of the standpipe. At this point, the ring 7 slides down the bolts 13 and the lower surfaces 5b of the cam lobes 5 engage with the complementary abutment surfaces on the portion 2 causing the cam members 4 to swing outwardly so that the lobes 5 project into the locking recess 6, as shown in Fig. 1. The raising and lowering mechanism is now removed, the driving shaft positioned in co-operation with the head 25 and the shank 21 rotated so as to separate the lower portion 2 and the member 15 and move the cam members 4 upwards so that their upper surfaces 5a come into engagement with the complementary surface 6a of the locking recess 6. Following this engagement, further rotation of the shank 21 causes the member 15 to move downwardly, compressing the sealing ring 17 against the shoulder 20. The driving shaft is then removed and the shank 21 retained in position, for example by a thread locking device (not shown). The pressure vessel to which the standpipe 1 leads may now be subjected to internal pressure and the plug cannot then be removed until the internal pressure is relieved since this acts on the lower portion 2 via the member 15 urging the cam members 4 into the locked position in which they will remain even if the shank 21 is rotated to bring the lower portion 2 and the member 15 into abutment. The means of applying the locking fore described, viz. by means of the screw threaded shank 21, is not essential and may be replaced by a cam lever arrangement, or the force may be applied hydraulically or pneumatically.