Abstract: A panel for elevated access floors is disclosed in which the panel is formed of reinforced expanded lightweight concrete. The reinforcing is provided by a grid including two arrays of parallel reinforcing rods which extend parallel to the associated panel edges and perpendicular to the rods of the other grid. A frame is provided by the grid around the two arrays. The grid is located adjacent to the lower surface of the body and divides the body into a plurality of square zones. Located in each zone, excepting the zones at the corners, is a pyramid-shaped cavity which extends from a base at the lower surface of the panel upwardly at about 45.degree. to an apex spaced from the upper surface of the panel. The presence of the pyramid-shaped cavities does not materially reduce the strength of the panel when compared to a similar panel without such cavities, but reduces the weight of the panel and the material required to manufacture the panel.

Abstract: An overload protective system continuousy monitors the forward overturning moment on a counterbalanced lift truck and prevents further raising of the carriage or further forward tilting of the mast when the tilting moment is excessive.

Abstract: When the load moment on a counterbalanced lift truck exceeds a predetermined magnitude, a blocking valve automatically prevents forward tilting of the mast and elevation of the load. The load moment is sensed by the pressure differential across the tilt jack and the blocking valve is actuated by the pressure differential. In order to prevent the blocking valve from becoming locked up, when the tilt jack is contracted to the end of its stroke, a spring-biased unloading valve is incorporated in the tilt jack piston. Abuse of the truck is reduced and operator safety is improved further by the provision of a second blocking valve which prevents lifting loads when the tilt jack is at the end of its extension stroke, that is when the mast is tilted forwardly as far as permitted by the tilt jack. In this condition the second blocking valve will close preventing further raising of the load. However, retraction of the tilt and lift jacks is permitted even though the blocking valves are in their closed positions.