Assertion: bore | /r/HasProperty | wall
Facets:
Source sentences:
text: Thus provision is made for selectively and independently expanding the separate rings 42 into clamped engagement with the bore wall where they serve as abutments against which extension of the associated rams 45 may act to urge the frame and excavating assembly in the direction of desired operation, and, conversely, for selectively and independently contracting the separate rings away from the bore Walls to a condition in which retraction of the rams 45 operates to advance the associated ring along the frame 27 and bore to a new position with respect to the latter; it being fully apparent that the said rings may be shifted, expanded, and contracted in an alternative sequence effective to permit maintenance of continuous pressure through one or the other of the ram 45 pairs urging the excavating head in the direction of desired penetration, or conversely effective, when desired, to apply retraction of the ram pairs for reverse travel of the frame and head assembly.