Danfoss LDU20, LDU24 Service guide
Service Manual
LDU20/24
Closed Circuit Axial Piston Transmission
www.danfoss.com
Service Manual
LDU20/24 Closed Circuit Axial Piston Transmission
Revision history Table of revisions
Date Changed Rev
June 2021 Added Size 24, Changed document number from 'AX00000049' and '11071687' to
'AX152886481311'
July 2017 Updated to Engineering Tomorrow 0202
March 2014 Danfoss layout BA
January 2011 First edition AA
0304
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Service Manual
LDU20/24 Closed Circuit Axial Piston Transmission
Contents
Introduction
Overview..............................................................................................................................................................................................5
Warranty.............................................................................................................................................................................................. 5
General Instructions........................................................................................................................................................................ 5
Remove the unit.......................................................................................................................................................................... 5
Keep it clean..................................................................................................................................................................................5
Lubricate moving parts.............................................................................................................................................................5
Replace all O-rings and gaskets............................................................................................................................................. 5
Secure the unit.............................................................................................................................................................................6
Safety Precautions............................................................................................................................................................................6
Unintended machine movement..........................................................................................................................................6
Flammable cleaning solvents.................................................................................................................................................6
Fluid under pressure..................................................................................................................................................................6
Personal safety............................................................................................................................................................................. 6
Hazardous material.................................................................................................................................................................... 6
Symbols Used in Danfoss Literature..........................................................................................................................................7
General Description
Basic Design........................................................................................................................................................................................8
Key Features....................................................................................................................................................................................... 8
Typical Applications........................................................................................................................................................................ 8
Schematic Diagram..........................................................................................................................................................................8
Operation
HPRV (High Pressure Relief Valve) ............................................................................................................................................. 9
Charge Check Relief Valve with Orifice............................................................................................................................... 9
Bypass Function..............................................................................................................................................................................10
CPRV (Charge Pressure Relief Valve)....................................................................................................................................... 11
Control............................................................................................................................................................................................... 11
Direct Displacement Control................................................................................................................................................11
Control Handle Requirements............................................................................................................................................. 11
Operating Parameters
Overview........................................................................................................................................................................................... 12
Input Speed......................................................................................................................................................................................12
System Pressure..............................................................................................................................................................................12
Input Power......................................................................................................................................................................................12
Charge Pressure..............................................................................................................................................................................13
Case Pressure...................................................................................................................................................................................13
Viscosity.............................................................................................................................................................................................13
Temperature.................................................................................................................................................................................... 13
Technical Specifications
General Specifications..................................................................................................................................................................14
Physical Properties.........................................................................................................................................................................14
Operating Parameters..................................................................................................................................................................14
Fluid Specifications....................................................................................................................................................................... 15
Fluid and Filter Maintenance
Fluid and Filter Recommendations......................................................................................................................................... 16
Pressure Measurements
Port Locations and Gauge Installation...................................................................................................................................17
Initial Startup Procedure
Startup Procedure..........................................................................................................................................................................18
Troubleshooting
Overview........................................................................................................................................................................................... 19
System Operating Hot..................................................................................................................................................................19
Transmission Operates Normally in One Direction Only.................................................................................................19
System will not Operate in Either Direction.........................................................................................................................19
System Noise or Vibration...........................................................................................................................................................20
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Service Manual
LDU20/24 Closed Circuit Axial Piston Transmission
Contents
Sluggish System Response.........................................................................................................................................................20
Required Tools and Standard Procedures
Required Tools................................................................................................................................................................................ 21
Standard Procedures.................................................................................................................................................................... 21
Charge Check/HPRV Adjustments...........................................................................................................................................21
Checking for proper charge check/HPRV operation....................................................................................................21
Minor Repair
Shaft Seals.........................................................................................................................................................................................22
Removal........................................................................................................................................................................................22
Inspection....................................................................................................................................................................................22
Assembly......................................................................................................................................................................................22
Charge Check/HPRV......................................................................................................................................................................23
Removal........................................................................................................................................................................................23
Inspection....................................................................................................................................................................................23
Reassembly................................................................................................................................................................................. 23
Bypass Valve.....................................................................................................................................................................................24
Removal........................................................................................................................................................................................24
Inspection....................................................................................................................................................................................24
Reassembly................................................................................................................................................................................. 24
Torque Chart
Plug Size and Torque Chart........................................................................................................................................................25
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Service Manual
LDU20/24 Closed Circuit Axial Piston Transmission
Introduction
Overview
This manual includes information on the installation, maintenance, and minor repair of LDU20/24
transmission (HST). It includes a description of the unit and its individual components, troubleshooting
information, and minor repair procedures.
Performing minor repairs may require removal from the vehicle/machine. Thoroughly clean the unit
before beginning maintenance or repair activities. Since dirt and contamination are the greatest enemies
of any type of hydraulic equipment, follow cleanliness requirements strictly. This is especially important
when changing the system filter and when removing hoses or plumbing.
A worldwide network of Danfoss Authorized Service Centers is available for major repairs. Danfoss trains
and certifies Authorized Service Centers on a regular basis. You can locate your nearest Authorized
Service Center using the distributor locator at www.sauer-danfoss.com.
Warranty
Performing installation, maintenance, and minor repairs according to the procedures in this manual will
not affect your warranty. Major repairs requiring the removal of the units center section voids the
warranty unless completed by a Danfoss Global Service Partner.
General Instructions
Follow these general procedures.
Remove the unit
Prior to performing major repairs, remove the unit from the vehicle/machine. Chock the wheels on the
vehicle or lock the mechanism to inhibit movement. Be aware that hydraulic fluid may be under high
pressure and/or hot. Inspect the outside of the HST and fittings for damage. Cap hoses and plug ports
after removal to prevent contamination.
Keep it clean
Cleanliness is a primary means of assuring satisfactory HST life, on either new or repaired units. Clean the
outside of the HST thoroughly before disassembly. Take care to avoid contamination of the system ports.
Cleaning parts using a clean solvent wash and air drying is usually adequate.
As with any precision equipment, keep all parts free of foreign materials and chemicals. Protect all
exposed sealing surfaces and open cavities from damage and foreign material. If left unattended, cover
the transmission with a protective layer of plastic.
Lubricate moving parts
During assembly, coat all moving parts with clean hydraulic fluid. This assures that these parts are
lubricated during start-up.
Replace all O-rings and gaskets
Danfoss recommends you replace all O-rings, seals, and gaskets during repair.Lightly lubricate all O-rings
with clean petroleum jelly prior to assembly. Grease must be soluable in hydraulic fluid.
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LDU20/24 Closed Circuit Axial Piston Transmission
Introduction
Secure the unit
For major repair, place the unit in a stable position with the shaft pointing downward. It is necessary to
secure the transmission while removing and torquing components and fasteners.
Safety Precautions
Always consider safety precautions before beginning a service procedure. Protect yourself and others
from injury. Take the following general precautions whenever servicing a hydraulic system.
Unintended machine movement
Warning
Unintended movement of the machine or mechanism may cause injury to the technician or bystanders.
To protect against unintended movement, secure the machine or disable/disconnect the mechanism
while servicing.
Flammable cleaning solvents
Warning
Some cleaning solvents are flammable. To avoid possible fire, do not use cleaning solvents in an area
where a source of ignition may be present.
Fluid under pressure
Warning
Escaping hydraulic fluid under pressure can have sufficient force to penetrate your skin causing serious
injury and/or infection. This fluid may also be hot enough to cause burns. Use caution when dealing with
hydraulic fluid under pressure. Relieve pressure in the system before removing hoses, fittings, gauges, or
components. Never use your hand or any other body part to check for leaks in a pressurized line. Seek
medical attention immediately if you are cut by hydraulic fluid.
Personal safety
Warning
Protect yourself from injury. Use proper safety equipment, including safety glasses, at all times.
Hazardous material
Warning
Hydraulic fluid contains hazardous material. Avoid prolonged contact with hydraulic fluid. Always
dispose of used hydraulic fluid according to environmental regulations.
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Service Manual
LDU20/24 Closed Circuit Axial Piston Transmission
Introduction
Symbols Used in Danfoss Literature
WARNING may result in injury
CAUTION may result in damage to product or property
Non-reusable part, use a new part
External hex head
Internal hex head
Lubricate with hydraulic fluid
Apply grease / petroleum jelly
Inspect for wear or damage
Clean area or part
Be careful not to scratch or damage
Note correct orientation
Torque specification
Press in – press fit
Measurement required
Pull out with tool – press fit
Flatness specification
Parallelism specification
Cover splines with installation cylinder
Mark orientation for reinstallation
The symbols above appear in the illustrations and text of this manual. They are intended to communicate
helpful information at the point where it is most useful to the reader. In most instances, the appearance
of the symbol itself denotes its meaning. The legend above defines each symbol and explains its purpose.
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MB1
MA2
MB2
L1
L2
L3
S
M3
P400004
Service Manual
LDU20/24 Closed Circuit Axial Piston Transmission
General Description
Basic Design
LDU20/24 is a U-style HST transmission, including a closed circuit variable displacement piston pump
with DDC (Direct displacement control) and a fixed motor. LDU20/24 is specially designed with optimized
performance, size, and cost, in order to fulfill the demand of the mobile applications marketplace. This
document provides the detailed specifications and features for LDU20/24.
Key Features
Easy to use design as Complete Hydrostatic Transmission package for Turf care machine & Compact
•
Utility Tractor of up to 26kw[35PS]
Compact design
•
U-style layout in One housing with Z-shaft configuration
•
Available external charge
•
Bypass valve for the pulling of the vehicle
•
Same shaft center distance as BDU21 85mm…Between pump and motor shaft
•
Same drive line design is available between BDU21 and LDU20/24
•
Best in class Efficiency by Female Piston & Male slipper design…Can reach approximately 80% overall
•
efficiency
Longer life kit, Higher Duty capability in most compact design in this class of HST
•
Low operating force
•
Serviced by a Worldwide Network of Danfoss
•
Typical Applications
Schematic Diagram
Compact utility tractor
•
Turf care
•
Small agricultural machinery
•
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