Diamond DA 42 NG, Maintenance Manual

Page: 1368 / 2339

AIRCRAFT
Landing Gear
DA 42 NG AMM
Page 6
15 Mar 2018
32-30-00
Doc # 7.02.15
Rev. 4
3. Operation
Figures 4 thru 7 show the hydraulic schematic diagrams for the operation of the landing gear.
A. Retraction
When the pilot sets the landing gear selector handle to UP during flight the following occurs:
)
The electrical circuit to the hydraulic pump is made and the pump will operate if the system
pressure is less than 96.5 bar (1400 PSI). The retract solenoid valve is energized through the
LH main gear ‘weight-on-wheels’ micro switch and allows fluid to flow from the pump to the
retract side of the actuator. The extend solenoid valve is de-energized and allows fluid to flow
from the pump to the extend side of the actuator (Figure 4).
)
The pump pressure switch operates the pump as necessary to maintain the system pressure
at 96.5 - 113.8 bar (1400 - 1650 PSI). Fluid at pump pressure acts on both sides of the actuator
piston. The effective surface area of the retract side of the piston is larger than the effective
surface area on the extend side of the actuator piston. Because the same fluid pressure is
acting on different effective areas of the actuator pistons the resulting ‘differential pressure’
acting on the piston causes the actuator to move the landing gear leg towards the retract
position.
)
The initial movement of the hydraulic actuators towards the retract position releases the folding
stay latching mechanism. The folding stay can then fold into the landing gear bay with the
landing gear.
)
When the landing gear is fully retracted the nose landing gear UP micro switch operates and
the extend solenoid valve is energized and moves to the ‘full pressure’ position (Figure 5). Fluid
returning from the extend side of the actuators flows through the extend solenoid valve and back
into the reservoir. The full pump pressure acting on the retract side of the actuator pistons holds
the landing gear in the fully retracted position.
)
The pump pressure switch operates the pump as necessary, to maintain the system pressure
at 96.5 - 113.8 bar (1400 - 1650 PSI). If there are no internal leaks in the system the hydraulic
accumulator will maintain the pressure in the system without the hydraulic pump operating.