These valves use a spherical shaped closure member with a cylindrical bore through the member for passage of flow. This spherical closure member has to be rotated by 90 degrees to bring the valve from fully closed position to fully open position. This type gets the name from the shape of the closure member. If the diameter of the cylindrical bore is same as that of the connecting pipe, the valve is known as full bore valve. If this diameter is less than that of the connecting pipe, the valve is known venturi style valve. These valves rotary stem motion.