Pump 1 delivers hydraulic fluid, at a pressure controlled by relief valve 2, through check valve 3 into a directional valve with spool 4 which directs the fluid to ends A of power cylinders 5. This moves pistons 6 which retract the landing ghear and skid. From ends D of the cylinders, fluid is discharged through valves 7 and the directional valve to the tank. When the landing gear is in the retracted position, limit switches switch off the electric motor that drives pump 1. In the extreme left-hand position of valve spool 4, the landing gear and skid are lowered. At this, fluid is delivered by the pump through the directional valve and check valves 7 to ends D of power cylinders 5. Fluid from ends A is discharged through the directional valve to the tank. Valve 3 serves as a hydraulic seal to hold the landing gear and skid in the lowered position. In the extreme right-hand position of valve spool 4, corresponding to emergency lowering of the landing gear and skid, the ports for delivering fluid from the pump are blocked off and ends A are connected through an axial passage in spool 4 to emergency tank 10. In this case, fluid for lowering is delivered by high- and low-pressure manual pumps 8, the low-pressure pump being switched off at the end of the lowering operation by valve 9. Fluid from manual pumps 8 is delivered along pipelines shown by dash lines through valves 7, forcing back their plungers, into ends D of power cylinders 5, thereby lowering the landing gear.
$4278$CHP,AL$