17 July 2017

Unintended Movement of Drill Motor

Technical Bulletin Number: TB001

To advise operators and owners of Alminco Scorpion Crawler Drill Rigs on the requirements for regular inspection and maintenance to prevent spool valve failures causing unintended movement of equipment and hence impacting operator safety.

Applicable to:
All Alminco Scorpion models including both Air/Hydraulic and Electric/Hydraulic options manufactured prior to 01/01/2014.
Incident Description
During weekly maintenance, a fitter discovered that the drill motor slowly turned whilst the directional control valve (spool valve) was in the centre neutral position. The unintended movement was found to be caused by the incorrect seating of the spool valve which allowed pressurised hydraulic oil to bypass to the drill motor.
Inspection and Repair
Inspection of the disassembled spool valve revealed a broken star washer and retaining E-clip. The broken parts prevented the spool valve’s normal spring to the centre action. It is understood that this failure occurred after approximately five years operation without internal maintenance of the spool valve. The star washer and E-clip have since been replaced and the crawler has been returned to service. Future maintenance will include replacement of the star washer with a stronger design.

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