Mining Publication: Performance and Safety Considerations of Hydraulic Support Systems

• Longwall shields
• Pressure

Hydraulic cylinders are used in several roof support systems, such as longwall shields and mobile roof supports, to provide critical ground control. Many state-of-the-art hydraulic support systems operate at pressures as high as 7,000 psi to provide the necessary support capacities. Pressure in the upper stages of multi-stage cylinders can be intensified by a factor of 2 or 3 providing pressures of 20,000 psi or greater. A proper understanding of the operation of these high pressure systems is necessary to safely maintain and repair these support systems. Likewise, the performance characteristics need to be fully understood to evaluate the impact of design parameters on the capability of the support to maintain effective ground control. This paper examines the basic operating principles of state-of-the-art hydraulic cylinders and discusses relative issues pertaining to:(1) setting loads,(2) support stiffness,(3) yielding behavior,(4) errors in assessing support loading, and (5) hydraulic failure mechanisms and how to detect them.