Mine roof support hydraulic control system - has cylinder operated by main valve and low pressure operated changeover valve

摘要

The mine system includes two roof members with angle shaped end members to close the gap between them, and also an adjacent unit. The travel of each end member is controlled by a hydraulic cylinder parallel with the roof member. Each cylinder is in turn controlled by a valve arrangement. A line connects these valves with the chamber of the cylinder, and the changeover valve is connected to a supply line at a lower pressure than the pressure required to operate the cylinder. This valve operates automatically in response to the load on the cylinder. The other valve is the operating valve, connecting the high pressure supply to the cylinder.