| 摘要 |
A telescopic prop for use in mine workings extends and retracts over three stages. The prop has an outer main base member 1 with respective first, second and third concentric inner members 2, 3, 4 disposed one within another. The first inner member has a piston 6 in which is arranged a non-return valve 23 which normally shuts off communication between a working chamber 20 associated with the first and base members and the working chambers 22, 27, 29 pertaining to the other members. A plunger 24 is provided to open the non-return valve when the first inner member is nearly fully retracted inside the base member so that after retraction of this stage the other stages can be retracted. The second or intermediate member also employs a piston 9 which is connected via a rod 13 with an auxiliary piston 15 disposed in a working chamber associated with the uppermost third member. The areas of the working faces of the respective pistons are designed so that the prop has a practically equal supporting force over the its entire range of displacement. |
