| 摘要 |
An hydraulic prop having a relatively movable piston and cylinder which are surrounded by an outer guide tube provided with a closed end which is normally spaced away from an opposing end of the piston by spring means but which moves telescopically in relation to the piston if excess loads are applied to the prop, such relative movement between the piston and the outer guide tube causing the latter to actuate and move a plunger which, in turn, acts on a valve member in the piston so that liquid under pressure in a pressure chamber of the piston can flow out rapidly past the valve member and thus quickly relieve the prop of transitory excess loads such as those caused by rock falls or a partial collapse of the seam being worked.
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