Lower Kelly Valve
Definition - What does Lower Kelly Valve mean?
A Lower Kelly Valve is a full-opening valve installed just below the Kelly with an outside diameter equal to the outside diameter of the drill pipe tool joint. The valve is closed under pressure that removes the Kelly and is stripped into the hole when a closed IBOP valve is introduced above it to carry out the snubbing operations. The valve can be used to stop the mud loss while the Kelly is removed from the drill string.
Petropedia explains Lower Kelly Valve
Kelly valves are used as safety valves for drill pipes. The Lower Kelly Valve is an essential full-opening valve introduced immediately below the Kelly. The valve provides closure to stop mud loss when the Kelly is removed from the drill string. It is required to close the valve before the Kelly is disconnected so that the hoses and mud in the Kelly stay there. The valve can quickly pay for itself with the cost of biopolymers, oil mud and other expensive drilling fluids. Some of the valves are not designed to cope with the external pressure that is encountered in the stripping operations.