A Kelly Valve is a ball valve that is installed in-line with the drill string. When used as an upper Kelly Valve, they are closed when needed to control the pressure of a blowout. When used as a lower Kelly Valve, they are closed to prevent drilling fluid loss during periods when the Kelly is disconnected. When open, they allow free flow of the drilling fluid. Kelly Valves are also referred to as a “Kelly Cock” or a “Drill Pipe Safety Valve”.

A rotary valve actuator is used to open or close the Kelly Valve during drill string rotation. As shown in the schematic below, a hydraulically operated rack and pinion arrangement is used to turn the stem and ball of the Kelly Valve. The hydraulic fluid pressure is transmitted to the valve actuator via three rotary seals that are mounted in a non-rotating seal housing. In other words, the rotary valve actuator incorporates a compact hydraulic swivel.

Kalsi Seals provide a significant advantage in swivel-type applications such as this because of their cool operation and long sealing life. This advantage is achieved via a special lip design that introduces a thin film of hydraulic fluid between the lip and the mating shaft surface during rotation, allowing the lip to hydroplane. This minimizes friction, which reduces heat and wear.

 

Schematic of an Oilfield Kelly Valve Actuator