Danfoss LDU21C Service Manual page 19

Service Manual
LDU21C Closed Circuit Axial Piston Transmission
Initial Startup Procedure
Startup Procedure
©
Danfoss | April 2025
Always follow this procedure when starting up a new LDU21C installation or when the transmission has
been removed.
W
Warning
This service procedure may require disabling a vehicle/machine (raising the wheels off the ground, or
disconnecting the work function) to prevent injury to the technician and bystanders. Take the necessary
safety precautions.
1. Before installing the transmission, inspect the units for possible damage incurred during shipping
and handling.
2. Make certain all system components (reservoir, hoses, valves, fittings, heat exchanger, and so forth)
are clean before filling with fluid.
3. Install new system filter element(s) if necessary. Check that inlet line fittings are properly tightened
and free of air leaks.
4. Install the transmission.
5. Fill the housing by adding filtered hydraulic fluid to the upper case drain port.
6. Fill the reservoir with hydraulic fluid of the recommended type and viscosity. Use a 10-micron filler
filter. Ensure construction plug is closed after filling is complete.
7. Place the control lever in neutral, The control linkage must be disconnected from the transmission
during initial start up.
C
Caution
After start-up the fluid level in the reservoir may drop due to system components filling with fluid.
Damage to hydraulic components may occur if the fluid supply runs out. Ensure reservoir remains full
of fluid during start-up.
Air entrapment in oil under high pressure may damage hydraulic components. Check carefully for
inlet line leaks.
Do not run at maximum pressure until system is free of air and fluid has been thoroughly filtered.
8. Use a common method to disable the engine to prevent it from starting. Crank the starter for several
seconds. Do not to exceed the engine manufacturer's recommendation. Wait 30 seconds and then
crank the engine a second time as stated above. This operation helps remove air from the system
lines. Refill the reservoir to recommended full oil level.
9. Let the engine run for a minimum of 30 seconds at low idle to allow the air to work itself out of the
system. Check for leaks at all line connections and listen for cavitation. Check for proper fluid level in
reservoir.
10. When adequate charge pressure is established (as shown in model code), increase engine speed to
normal operating rpm to further purge residual air from the system.
11. Shut the off engine. Connect the control linkage. Start the engine, checking to be certain the pump
remains in neutral. Run the engine at normal operating speed and carefully check for forward and
reverse control operation.
12. Continue to cycle between forward and reverse for at least 5 minutes to bleed all air and flush system
contaminants out of the system loop.
Charge pressure may decrease slightly during forward or reverse operation.
13. Check that the reservoir is full. The transmission is now ready for operation.
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