| 摘要 |
A power tong 10 for making up and breaking apart threaded oilfield tubular connections includes a frame 11 having an open throat 20, a rotary ring 16 having an open throat 22, and a door 24 for closing over the open throat for safety. Hydraulic motor 42 is regulated by a control valve 52 for rotating the ring 16 which in turn rotates the oilfield tubular. A switch 46 responsive to the position of the door 24 controls the flow of air pressure to a cylinder 50, which renders active valve operator 54 which controls valve 52. According to the method of the invention, the door 24 must first be closed so that the switch 46 renders the valve operator 52 active, and the valve operator 52 must be reset once the door is opened before it can be manipulated to operate the motor control valve 52.
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