Power tongs with improved hydraulic drive

DETAILED DESCRIPTION A power tong is provided employing improved hydraulic circuitry for operating a three-speed tandem fluid motor to achieve forward and reverse hydraulic operation in any of three selected speed/torque ranges.
A valve block employing two 4 way/3 position valves is utilized, so that one of three selected tong speeds and either forward or reverse tong operation may be controlled by operating only two valve handles associated with the valve block.
The open throat tong includes drive means for automatically locking closed the pivotable tong door to prevent spreading of the tong.
A hydraulic tong latch motor adjacent the tong latch is powered for automatically locking the door when the tong is operated, and automatically unlocking the door when the tong is not being operated.
The door may be either manually or automatically opened and closed, but when closed may be automatically locked by the hydraulic latch motor.
The open throat tong according to the present invention may also include a plurality of pivotably movable or slidable heads with an increased composite angle of die engagement with the pipe.
Two dies preferably grip the pipe over a composite angle of at least 230.
degree.
to minimize the likelihood of galling or crushing the pipe.
It is therefore a feature of the invention to provide a tong with a reliable drive means capable of operating in one of at least three selected speeds/torque ranges.
It is a further feature of the present invention to provide a power tong with improved drive means which may be easily and quickly shifted from one speed to another speed by operating a minimum number of controls.
It is still another feature of the present invention to provide an open throat tong with a door latching mechanism for automatically locking the door when the tong is operated.
It is a further feature of the present invention to provide a tong with dies on a plurality of die carriers for effectively gripping the pipe over a large composite angle without crushing or damaging the pipe