PVC pipes are categorized into low-density, medium-density, high-density, and ultra-high molecular weight pipes, each requiring different welding methods and heating temperatures. Small diameters or thin-walled pipes use push-in connections, similar to heat-fused PPR pipes, but with different heating temperatures. Low-density pipes require 160 degrees, medium-density pipes 190 degrees, while high-density and ultra-high molecular weight pipes use 210-235 degrees. For large diameters, a heat-fusing machine is needed, with basic models including 160, 250, 315, 450, and 630. These employ butt welding, where pipes are directly melted and connected.