Mine roof supports

摘要

A mine roof support has a main roof-engaging structure 2 carried by hydraulic props 6 in known manner and an auxiliary roof-engaging structure at the front end of the main roof engaging structure. The auxiliary roof-engaging structure can be swung up and down and is itself of multi-part construction with one component 7 directly linked to the main structure and another selectively extendible forward component 8 mounted to the one component. One hydraulic piston and cylinder unit 9 is provided for swinging the auxiliary structure and for setting the structure against the roof and another such unit 10 is provided for selectively extending and retracting the forward component thereof. A hydraulic control arrangement 16-18 associated with the units ensures that when the forward component is being advanced the roof setting pressure acting on the auxiliary structure is automatically reduced.