SERVICE MANUAL & ICA
WIPLINE 3730 & 3900 FLOATS
Page 20
Revision K
P/N 1002551
4.1 OPERATION
The hydraulic system consists of an electro-hydraulic power pack with a non-reversing type pump and a hand
pump backup tied in between the return and pressure lines (see hydraulic schematic in figures 3 & 4). The pump
and reservoir assembly is mounted in the left float.
A pressure of between 500 psi and 1000 psi is maintained in the supply line. When the pressure falls below 500
psi, a pressure switch will activate the pump solenoid, providing power to the pump. When the pressure reaches
1000 psi, the pressure switch deactivates the solenoid and the pump motor is stopped. Figures 1 & 2 show the
electrical schematic of the system. A check valve on the output side of the pump retains pressure in the system
while the pump is off. The pump has an internal relief valve which directs oil back to the pump reservoir when the
line pressure exceeds 1200 psi. The system also has an external relief valve to protect against thermal expansion
when line pressure exceeds 1900 psi.
The selection of gear-up or gear-down is accomplished by a cockpit mounted control valve. Each float gear has
individual indicator lights on the control valve allowing the pilot to confirm that each gear has fully retracted or
extended.
4.2 MAINTENANCE
Maintenance of the hydraulic system is very easy; keep the proper amount of oil in the reservoir. A sight glass is
provided for this and the level should be kept in the upper 1/3 of the range. A screen is located in the reservoir
tank around the fluid pick up pipe and can be cleaned or checked at annual inspection or every 100-hour. Check
and replace if oil is dirty or if moisture is found (MIL-H-5601 Hydraulic Fluid, RED).
4.3 BLEEDING THE SYSTEM
Simply fill the reservoir with hydraulic oil and start a gear cycle. If the reservoir empties (i.e. fluid goes out of sight
in the sight glass), stop the cycle and add oil and complete the cycle. Continue with approximately four more gear
cycles after the fluid level in the reservoir normalizes (it will vary in level between up and down positions) and
check for leaks.
