In a floating-ball design the ball moves under differential pressure toward the downstream seat. Selection depends on size, pressure, seat material and operating torque.
In a trunnion design the ball is supported and the seat arrangement manages sealing loads. Do not assume DBB or a particular isolation function without confirming the design and testing documentation.
For actuator sizing provide maximum differential pressure, cycling duty, supply and fail position. The valve’s confirmed torque data is required before actuator selection.