Danfoss LDT 21 User manual

Service Manual
LDT 21/24/32
Closed Circuit Axial Piston Transmission
www.danfoss.com

Revision history Table of revisions
Date Changed Rev
June 2022 First edition 0101
Service Manual
LDT 21/24/32 Closed Circuit Axial Piston Transmission
2 | ©Danfoss | June 2022 AX417167456877en-000101

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.............................................................................................................................................................................5
Safety Precautions............................................................................................................................................................................5
Unintended machine movement..........................................................................................................................................6
Flammable cleaning solvents.................................................................................................................................................6
Fluid under pressure..................................................................................................................................................................6
Personal safety.............................................................................................................................................................................6
Hazardous material.................................................................................................................................................................... 6
General Description Basic Design........................................................................................................................................................................................7
Key Features....................................................................................................................................................................................... 7
Typical Applications........................................................................................................................................................................ 7
LDT Schematics.................................................................................................................................................................................7
Operations Check / High Pressure Relief Valve ............................................................................................................................................9
Check/High Pressure Relief Valve with Orifice.......................................................................................................................9
CPRV (Charge Pressure Relief Valve)....................................................................................................................................... 10
Control............................................................................................................................................................................................... 11
Direct Displacement Control................................................................................................................................................11
Control Handle Requirements............................................................................................................................................. 11
Operating Parameters Overview........................................................................................................................................................................................... 12
Input / Output Speed....................................................................................................................................................................12
System Pressure..............................................................................................................................................................................12
Input Power......................................................................................................................................................................................12
Charge Pressure..............................................................................................................................................................................12
Case pressure...................................................................................................................................................................................13
Viscosity.............................................................................................................................................................................................13
Temperature....................................................................................................................................................................................13
Technical Specifications General Specifications..................................................................................................................................................................14
Physical Properties.........................................................................................................................................................................14
Operating Parameters..................................................................................................................................................................14
Fluid Specifications....................................................................................................................................................................... 15
Fluid and Filter MaintenanceFluid and Filter Recommendations......................................................................................................................................... 16
Pressure Measurements LDT24 Port Locations and Gauge Installation..................................................................................................................... 17
Startup procedures 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...........................................................................................................................................................19
Sluggish System Response.........................................................................................................................................................20
Service Manual
LDT 21/24/32 Closed Circuit Axial Piston Transmission
Contents
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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
Torque Chart LDT24 Plug Size and Torque Chart..........................................................................................................................................24
Service Manual
LDT 21/24/32 Closed Circuit Axial Piston Transmission
Contents
4 | ©Danfoss | June 2022 AX417167456877en-000101

Overview
This manual includes information on the installation, maintenance, and minor repair of LDT21/24/32
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.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.
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.
Service Manual
LDT 21/24/32 Closed Circuit Axial Piston Transmission
Introduction
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Unintended machine movement
W
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
W
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
W
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
W
Warning
Protect yourself from injury. Use proper safety equipment, including safety glasses, at all times.
Hazardous material
W
Warning
Hydraulic fluid contains hazardous material. Avoid prolonged contact with hydraulic fluid. Always
dispose of used hydraulic fluid according to environmental regulations.
Service Manual
LDT 21/24/32 Closed Circuit Axial Piston Transmission
Introduction
6 | ©Danfoss | June 2022 AX417167456877en-000101

Basic Design
LDT21/24/32 is a U-style hydrostatic transmission with a Z-shaft configuration, including a closed circuit
variable displacement piston pump with DDC (Direct displacement control) and a fixed motor.
LDT21/24/32 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 LDT21/24/32.
Key Features
•Easy to use design as a complete hydrostatic transmission package for compact utility tractors
ranging from 22 hp to 40 hp
•Compact design
•U-style layout in one housing with Z-shaft configuration
•Requires external charge flow
•LDT21/24 feature 85mm between pump and motor shaft centers, identical to BDU21 and LDU20.
LDT32 shaft center distance is 105mm
•Best in class efficiency, utilizing female piston and male slipper design; overall efficiency of
approximately 80% is possible
•Improved life kit, higher duty cycle capability while providing the most compact design in this class of
hydrostatic transmission
•Low trunnion operating force
•Serviced by Danfoss' global network
Typical Applications
•Compact utility tractor
LDT Schematics
LDT21 hydraulic schematic
Service Manual
LDT 21/24/32 Closed Circuit Axial Piston Transmission
General Description
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LDT24 hydraulic schematic
MB1 EM3 L3 MB2
MA2
L2L1MA1
LDT32 hydraulic schematic
MB1 EL3 MB2
MA2L2L1MA1
Service Manual
LDT 21/24/32 Closed Circuit Axial Piston Transmission
General Description
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Check / High Pressure Relief Valve
LDT21/24/32 is equipped with a combination high pressure relief and charge check valve. The high-
pressure relief function is a dissipative (with heat generation) pressure control valve for the purpose of
limiting excessive system pressures. The charge check function acts to replenish the low-pressure side of
the working loop with charge oil. Each side of the transmission loop has a dedicated HPRV valve that is
non-adjustable with a factory set pressure. When system pressure exceeds the factory setting of the
valve, oil is passed from the high pressure system loop, into the charge gallery, and into the low pressure
system loop via the charge check or into the transmission case via charge pressure relief valve (CPRV).
C
Caution
The High Pressure Relief Valve (HRPV) function is intended for short duration over-pressure protection /
regulation only.
Check/High Pressure Relief Valve with Orifice
Check/High pressure relief valve with orifice
As an option, LDT21/24/32 offers check / HPRV with an orifice produce a larger neutral deadband.
In some applications, it is desirable to use check / HPRV with an orifice to expand null dead band, which
would help provide a larger margin of safety for vehicle movement in neutral and provide easier
adjustment of the vehicle linkage for machine neutral. The orifice connects the working loop, which is a
main hydraulic circuit, to a charge circuit. It always allows some internal leakage to ensure the expanding
null dead band around neutral position of control shaft. However, it decreases the volumetric efficiency,
particularly at high system pressure in the working loop. Check / HPRV with an orifice has possibility to
increase downhill creep. It is recommended to install the orifice in a specific working loop, which is
pressurized when the vehicle moves in reverse.
The HPRV are set at the following flow rates
Valve LDT21 LDT24 LDT32
Check / HPRV without
orifice 6 l/min [1.6 US gal/min] 4.7 l/min [1.3 US gal/min] 4.7 l/min [1.3 US gal/min]
check / HPRV with orifice 18 l/min [4.8 US gal/min] N/A N/A
P400005
C
Caution
HPRVs are factory set at a low flow condition. Any application or operating condition which leads to
elevated HPRV flow will cause a pressure rise with flow above a valve setting. Consult factory for
application review.
C
Caution
The High Pressure Relief Valve (HRPV) function is intended for short duration over-pressure protection /
regulation only.
Service Manual
LDT 21/24/32 Closed Circuit Axial Piston Transmission
Operations
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CPRV (Charge Pressure Relief Valve)
The charge pressure relief valve maintains charge pressure at a designated level above case pressure. The
charge pressure relief valve is a direct acting poppet valve which opens and discharges fluid to the
hydrostatic transmission case when pressure exceeds a designated level. For external charge flow the
CPRV is set according to below table. The charge pressure relief valve setting is specified on the model
code of the unit.
Charge Pressure Relief Valve settings for external charge supply
LDT Size Flow, l/min [US gal/min]
LDT21 7.0 [1.9]
LDT24 10.8 [2.9]
LDT32 13.8 [3.6]
LDT21 CPRV LDT24 CPRV LDT32 CPRV
Charge Pressure
Charge Pressure
Charge Pressure
Service Manual
LDT 21/24/32 Closed Circuit Axial Piston Transmission
Operations
10 | ©Danfoss | June 2022 AX417167456877en-000101