This type of compensator has two working bellows at the ends, a balancing bellows in the middle, plus tie rods and end plates. The balancing bellows has twice the effective area of the working ones. Here's the trick: the axial thrust from internal pressure in the working bellows pushes outward, but the balancing bellows pushes back in the opposite direction via the tie rods. So the thrust cancels out—no axial thrust acts on the pipeline or equipment. Instead, they only feel the stiffness reaction force from the expansion joint's displacement. And compared to blind flange forces, this reaction force is like tens of times smaller, making it way easier to fix the equipment and pipes. Just so you know, this compensator can only absorb axial displacement.

It uses two different bellows sizes (usually the average diameter of one is 1.4x the other). Main job: absorb axial displacement and balance pressure thrust. The thrust is handled by the bellows' own structure, so fixed supports only need to account for the bellows' elastic force and pipe friction.

The picture shows a typical setup. The two pieces of equipment have sensitive load needs—both pressure and displacement on the flange parts need to be minimal. When this expansion joint absorbs all the axial displacement, the equipment can expand/contract due to temperature changes. If the pipe between equipment or the expansion joint's diameter is 4x larger than the main pipe, go for this straight pipe pressure balanced type.