Kelly valve is a manually operated ball-type valve for the drill stem, divided into upper and lower sections. The upper Kelly valve is connected between the lower end of the swivel and the upper end of Kelly. The lower Kelly valve is connected between the upper end of the drill pipe and the lower end of Kelly or the lower end of Kelly saver subs. The Kelly valve can be opened or closed off by simply turning a special operating wrench 90° according to the indicated direction.
The sealing principle for the Kelly valve is to ensure a close seat between the ball and the ball seat. The lower seat is supported by a spring. The force provided by the spring keeps the ball securely in place with a lower seat.
During normal drilling operation, the hole is kept unblocked by turning the stem to the “on” position; In case of kick or blowout, turn the operating stem to the “off” position to close off the internal bore of the drill string, the kick or blowout accident is avoided due to a high-pressure sealing situation between the ball and the ball seat.
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