Ladder working limit based ladder stopping device for aerial ladder truck

In an aerial ladder truck assembly having a turntable unit mounted on the rear portion of the truck, a ladder support pillar unit mounted on the turntable unit, a ladder support frame unit pivotally mounted on the ladder support pillar unit, ladder means mounted on the ladder support frame unit, hydraulic cylinder means operatively positioned between the ladder support pillar unit and the ladder support frame unit to vertically swing the ladder means, operating lever means for actuating said hydraulic cylinder means, drum means to extend and contract the ladder means, hydraulic driving means for actuating the drum means, operating lever means for actuating said hydraulic driving means, hydraulic pump means for actuating the hydraulic cylinder means and the hydraulic driving means, and control means for operating said hydraulic cylinder means and said hydraulic driving means respectively, the improvement of a safety mechanism for preventing the vertical swinging and the extension of the ladder means beyond safe working limits, said safety mechanism including first indicator means operatively connected with the ladder means for indicating the amount of extension of the ladder means, second indicator means operatively connected with the ladder means for indicating the vertical swing of the ladder means, first solenoid valve means operatively associated with the hydraulic driving means for automatically stopping the extension and contraction of said ladder means, second solenoid valve means operatively associated with the hydraulic cylinder means for automatically stopping the raising and lowering of said ladder means, and electrical circuit means operatively connected to said first indicator means and to said second indicator means on the one side and to said first solenoid means and said second solenoid means on the other side, said electrical circuit means including switching means whereby when said ladder means reaches a maximum safe extension point at the particular vertical inclination angle of the ladder means as indicated by said first indicator means and said second indicator means, said switching means of said electrical circuit means will energize said first and second solenoid means to prevent any further movement of the ladder means beyond the safe point of the ladder means.