Transversely removable gantry loader

A gantry loader comprising

• a horizontally disposed support beam,
• a railway rail secured to said support beam, said rail including a straight portion terminating in a head having an end face extending substantially perpendicularly to said straight portion and opposing portions projecting in a direction parallel to said end face outwardly beyond said straight portion, and having substantially flat surfaces parallel to said straight portion,
• a loader assembly including a carriage selectively displaceable along said beam, said carriage having
• a first wheel mounted for rotation about an axis parallel to said straight portion and having a substantially flat surface for rollingly engaging the flat surface of one projecting portion of said head,
• a second wheel mounted for rotation about an axis perpendicular to said straight portion for rollingly engaging the face of said rail head,
• a third wheel mounted for rotation about an axis parallel to said straight portion for rollingly engaging the flat surface of the other projecting portion of said head, said third wheel including a peripheral step having a base portion selectively facing the flat surface of said other projecting portion and having a side wall surface for rollingly engaging the side of said head opposite from said end face,
• said third wheel being selectively displaceable in a plane perpendicular to its axis from a retracted position remote from said rail whereat said loader assembly can be transversely displaced away from said rail to an advanced position whereat the base and side wall surface of said step engage said other projecting portion to prevent the disassociation of said loader assembly from said rail, and
• means for selectively maintaining said third wheel at said advanced position.