The main difference is whether they contain hydraulic units which can provide hydraulic strength to move or remove the two pipes while butt fusion process, and keep a certain & stable pressure while two pipes are bonded. A manual butt welding machine doesn't consist of a hydraulic unit. So the pipe move/remove shall be made manually. Obviously, the hydraulic welding machine is more convenient, labor-saving and intelligent than the manual type, so the manual one is only suitable for the machines under 315mm.