ARRANGEMENT FOR CONTROLLING BOOM FOR ROCK DRILLING UNIT

摘要

An arrangement for limiting the swing angle of a boom (1) for a rock drilling unit when the boom (1) is being lifted and lowered. In the arrangement, a control member (12) is coupled to the boom (1), turning therewith, said member comprising a slot (13) having a movable dowel pin (14). The dowel pin (14) is coupled to control a relief valve (16) so that when the boom (1) is being lifted or lowered, and when it tends to turn outside the widest permissible swing angle, the control member controls the relief valve (16) so that it lets hydraulic fluid into the swing cylinder (4) for turning the boom to a reverse direction.