is readily positioned around side plate 21 with head boot 13 surrounding side plate 21 and upper plate 16 removed from head studs 18 it is a simple matter to slide head boot 13 and side plate 21 down around head studs 18 thereafter upper plate 16 may be positioned as shown in fig2 and connected to head studs 18 by means of screws 19 in this manner upper plate 16 lower plate 17 and the combination of side plate 21 and head boot 13 form an interior chamber 22 it is also seen that the new construction of head boot 13 eliminates the necessity for circumferential steel bands and makes the replacement of head boot 13 a relatively simple matter attached to the interior of side plate 21 is an internally threaded coupling or boss 24 which communicates by means of a hole 25 in side plate 21 with the space between head boot 13 and side plate 21 boss 24 may be welded to side plate 21 as shown at 26 a conventional male branch tee 27 threadingly engages coupling 24 as seen in fig2 one end of a piece of tubing 28 may be attached between connector 15 and one branch 27a of tee 27 it will thus be appreciated that sealing fluid entrant through connector 15 will be directed via tubing 28 to the region between side plate 21 and boot 13 to thereby expand boot 13 outwardly to seal jacket 5 as explained more fully in the grenci patent another length of tubing 29 coiled so as to provide flexibility.