SEMI-TRAILER AIR SUSPENSION
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PATENT No, 854,233 shows modifications which allow the frame height of a tractive unit to be adjusted (General Motors Corporation, Detroit, Michigan, U.S.A.). The object is to overcome the difficulty of coupling a semi-trailer designed for a tractive unit with leaf springs to one with air suspension and consequently a constant frame height, lower than that required for coupling.
Referring to the drawing, a manual control valve (I) is turned to allow air at high pressure to pass from the supply• tank (2), through automatic check valves, to air springs (4), by-passing levelling valves (3 and 5). As the pressure thus supplied will normally be greater than
that in the air springs, the level of the frame and the fifth-wheel table will be raised to the required height.
After coupling, the manual control valve is returned to its inoperative position, air in the springs is exhausted to atmosphere, complete loss being prevented by the check valves, and the levelling valves take over the height control.