that link insofar as as shown in fig3 the link 42 has a socket 44 in which engages a centralising pin 46 the wall of the socket 44 has aligned apertures 48 50 in which pegs 52 and 54 engage these pegs being carried by pivotable jaws 56 and 58 the jaws 56 and 58 are connected to the clamping device 60 having swingable arms 62 and 64 on the ends of which are provided guide rollers 66 and 68 as the bladder 38 inflates the rollers 66 which are held inwardly by spring action are caused to pivot to the position shown in fig1 which has the effect of moving the jaws 56 and 58 apart to remove the pegs 52 and 54 from the apertures 48 and 50 and the positioning device 40 and the device 60 with the rollers and jaws can be detached from the bladder and the connecting tube 42 so that it can be pulled along the line 10 away from the inflated bladder a series of additional pressure pipes and corresponding bleed pipes 70 72 four in all extend to the outside of the bladder 38 and are removably attached to the positioning device 40 device 40 is moved to the other end of the main.