Abstract: A kelly cock valve for a drill rig uses a sliding gate to open and close the flow passage through the drill string. The valve has a body with a longitudinal passage through it. The gate is mounted in the body perpendicular to the flow passage. Pushrods extend from each end of the gate out through bonnets mounted to the body of the valve. The fluid cylinders are mounted on each side of the gate. Each fluid cylinder has a piston with a piston rod extending in opposite directions. The piston rods are connected to a beam that also connects to the pushrod. Hydraulic passages supply fluid to the cylinders to stroke the piston and thus move the gate valve between open and closed positions.