A Differential Pressure Unit (DPU) is made up of a Bellows Unit Assembly (BUA) and removable pressure housings, where flexible bellows respond to pressure changes. Inside, the bellows are connected to a valve system and drive mechanism that translates their movement into rotary motion through a torque tube. The bellows are filled with a stable liquid and balanced by a spring assembly that resists pressure differences. When pressure varies across the bellows, they move proportionally until the spring force balances the difference. In dual-bellows designs, built-in valves automatically close under excessive pressure to trap the liquid and prevent damage, providing protection in both directions.