in a more compact accordion like manner that the assembly 22 of the first embodiment which may be advantageous in circumstances where for example it is desired to reduce the load imposed on the forward end of the boom assembly 24 when in its stowed position the third embodiment 220 of the present invention illustrated in fig1 12 is yet another modification of the first embodiment of fig1 6 and again where the elements are essentially the same they have been designated by the same numbers in this third embodiment 220 the service line assembly 222 comprises two relatively long straight and rigid pipe sections 224 226 fig1 interconnected pivotally by a pair of short rigid pipe sections 228 230 and pipe swivel joints 232 234 and a pipe union 236 the service line assembly 222 is releasably suspended from the mono rail boom assembly 24 by trolleys 240 242 244 and 246 generally of the same type shown in fig5 and 9 whereby the service line is movable longitudinally with respect to the boom assembly as in the foregoing first and second embodiments in the stowed position of the service line assembly 222 fig1 the pipe sections 224 226 reside in a side by side parallel manner and of course are not connected at the pipe union 236 when the service line has been extended into its functional position fig1 the pipe union 236 is assembled to interconnect the pipe sections.