Rotary screw pump 1 delivers hydraulic fluid through directional valve 2 and valve member a of valve box 3 to ends A of power cylinders 4. This moves pistons 5 to lower landing gear 6. Fluid from ends D is discharged through directional valve 2 to the tank (see Fig. a). To retract the landing gear, valve 2 is turned to the position shown in Fig. b. Fluid from the pump is delivered through valve 2 to ends D, moving pistons 5 and retracting landing gear 6. Fluid from ends A is discharged through valve member d of valve box 3 and valve 2 to the tank. Upon a failure in the hydraulic system, emergency lowering of the landing gear is due to its own weight. In this case, valve 2 is turned to the neutral position (shown in Fig. c). Since in lowering the landing gear by its own weight it is lowered at such a high rate that pump 1 is incapable of filling the spaces evacuated by pistons 5, these spaces are filled with fluid directly from the tank through valve member b which opens due to the vacuum in ends A. Fluid discharged from ends D passes through valve 2 and valve member b to ends A. Surplus fluid, due to the difference in effective areas of piston 5 in ends A and D, is discharged to the tank. The fluid is throttled by valve members a and d to prevent heavy impacts at the end of the piston strokes.
$4279$CHP,AL$