Abstract: The invention relates to the butt-welding of pipes of plastics materials. Equipment is alreaady known where pipe ends are first urged against a trimmer plate, and then urged against a heater plate to create beads of a required size at the ends of the pipes, following which the pipe ends are urged into abutting relationship for welding to occur. Particularly with automatic machines employing hydraulic power, the force applied between the pipe ends and the heater plate and subsequently between the pipe ends needs to include an allowance for the drag factor inherent in the pipeline and compensate for any frictional effect in the mechanical and hydraulic moving components, and which is a difficult calculation.