دیکشنری تخصصی مهندسی نفت - نسخه آنلاین

n: any assembly of pulleys on a common framework;in mechanics. one or more pulleys. or sheaves. mounted to rotate on a common axis. The crown block is an assembly of sheaves mounted on beams at the top of the derrick or mast. The drilling line is reeved over the sheaves of the crown block alternately with the sheaves of the travelling block. which is hoisted and lowered in the derrick or mast by the drilling line. When elevators are attached to a hook on a conventional travelling block. and when drill pipe is latched in the elevators. the pipe can be raised or lowered in the derrick or mast. See crown block, travelling block.