Four-way fittings are used for pipe joints and pipeline connectors. Also known as four-way pipe fittings or four-way connectors, they are employed where the main pipeline needs to branch off. Four-way fittings come in both equal and unequal sizes; equal-sized four-way fittings have all branches with the same diameter, while unequal-sized four-way fittings have the main pipeline branches with the same size, but the branch pipeline connections are smaller than the main pipeline connections. Four-way fittings are a type of pipe fitting used at pipeline branching points. The hydraulic expansion process for four-way fittings involves using an axial compensation method to form the branch pipe from the metal material. The process involves using a hydraulic press to inject liquid into a pipe blank of the same diameter as the four-way fitting, then synchronously moving the two horizontal cylinders of the hydraulic press to squeeze the pipe blank. As the pipe blank is compressed, its volume decreases, causing the liquid inside to increase in pressure. When the pressure reaches the required level for the branch pipe to expand, the metal material, under the combined pressure from the side cylinders and the liquid inside the pipe blank, flows along the mold cavity and expands to form the branch pipe.