| 摘要 |
A lower portion of water well casing in the ground is perforated by means of a toothed wheel journalled on the end of an arm pivotally carried by an elongated perforator body. The perforator body carries an air driven piston and actuator link connected to pivot the arm and wheel downwardly from an upward retracted position to a lower start position in which a point of one tooth and a flat end of an adjacent tooth contact the interior of the casing. In this start position the axis of rotation of the wheel is in an over-center position, below a line between the arm pivot axis and the point of the upper one of the two teeth that contact the casing surface. In this over-center start position, the perforator body is pulled upwardly so that the wheel teeth are pressed outwardly against the casing surface with great force by the over-center arrangement which urges the wheel axis closer to the casing. Each tooth has a truncated cutting end that extends along a line intersecting an outermost point of the adjacent tooth to provide optimum penetration of the casing wall.
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