Beam, WALKING

or WORKING. In beam engines the lever which transmits the motion of the piston-rod to the working point, usually through a pitman or main connecting-rod. In the earliest engines, where the work was all done by tension, the beam was of wood, and chains were attached to sectors at the two ends of the beam to keep the respective rods in line. Later, cast-iron beams were introduced, of a form resembling two parabolas back to back, and wrought-iron built-beams have been also used. The usual walking beam of American engines is a lozenge-shaped frame of wrought-iron, which is braced and kept from deformation by a cast-iron spider which carries the center and pins. The wrought-iron strap receives the push and pull of the piston, and the cast-iron bracing is under compre ion only.