sand jack

名词 n.
中文释义

英文释义

名词 n.
  1. A type of jack from which sand can be released gradually in small quantities when lowering something into position.
    — After being rolled into position, the span had to be lowered about 4 in. on to its bearings. This was accomplished by means of sand-jacks—a simple arrangement of piston and cylinder—by which movements to very fine limits are obtained by the controlled release of sand from an opening in the base of the cylinder.

词形变化

sand jacks plural
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