“An original equipment manufacturer recently reported to MSHA the test results of three recovered load-locking valves from mining equipment,” the agency said, though it did not indicate which company.

Two of the valves, it said, were replacements rather than OEM parts and, when tested, the valves had pressure relief below the rating indicated on it. The leakage rate also was beyond the producer’s specifications.

“The valves would have required adjustment or repair to perform to the stamped rating,” MSHA officials noted.

“Load-locking systems must be checked frequently for proper operation and adjustment to verify that machine structure will be supported in the raised position.”

Since 1981, the agency has required all units for loading or continuous mining to have a load-locking valve in the boom and head lift cylinders, and to be in compliance those must be present, maintained, and in proper working order.

Considered a violation are those that fail to support the machine structure in the raised position according to the agency’s Title 30 Code of Federal Regulations Part 75.503, which is “failure to maintain face equipment in permissible condition”.

MSHA has outlined compliance requirements for equipment utilising hydraulic cylinders to elevate cutting heads as well as conveyor booms that are required to feature a load-locking valve system. To meet federal criteria, the following must exist:

The load-locking valve must be attached directly to the cylinder port that is subject to the hydraulic pressure induced by the weight of the boom or cutting head, or directly to a section of steel tubing welded to the cylinder port and attached to the cylinder;

The rated working pressure of the load-locking valve must be greater than the maximum system operating pressure;

If the load-locking valve has overpressure relief capability, the overpressure relief setting shall be sufficient to allow proper operation of the load-locking valve;

If the load-locking valve is pilot operated, the hydraulic system shall be designed to ensure that the residual pilot pressure or line backpressure will not hold the load-locking valve open when the control valve is in the neutral position; and

Adequate hydraulic filtration shall be provided to ensure that the load-locking valve will operate properly throughout its normal service life, when the hydraulic system is subjected to rigorous everyday mining conditions.

A full printable copy of the alert is available on the agency’s website.