Technical Information

LDU20/24
Closed Circuit Axial Piston Transmission

www.danfoss.com

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission

Revision history

2 | © Danfoss | March 2024

Table of revisions
Date

ChangedRev

March 2024

Updated check & relief valve on model code

0304

June 2023

Minor correction

0303

June 2023

Fixed typo0302

May 2021

Added Size 24

0301

January 2021

Minor update in Physical Properties

0208

December 2020

Minor correction

0207

Novemebr 2020

Minor update

0206

June 2020

Changed document number from 'BC00000192' and 'L1124546' to 'BC152886483777'

0205

April 2019

Fixed Control Handle Requirements

0103

April 2018

Minor update

0102

June 2016

Converted to New Danfoss layout

0101

December 2014

Converted to DITA CMSADMarch 2013

Paint and Tag

ACMarch 2011

2nd edition

AB

January 2011

First editionAA

BC152886483777en-000304

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Contents
General Description
Basic Design........................................................................................................................................................................................4
Key Features....................................................................................................................................................................................... 4
Typical Applications........................................................................................................................................................................ 4
Schematic diagram.......................................................................................................................................................................... 4
Technical Specification
Physical properties...........................................................................................................................................................................5
Operation Parameters.....................................................................................................................................................................5
Fluid Specifications..........................................................................................................................................................................6
Operations
Check / High Pressure Relief Valve ............................................................................................................................................7
Check/High Pressure Relief Valve with Orifice.......................................................................................................................7
Bypass Function................................................................................................................................................................................ 8
CPRV (Charge Pressure Relief Valve)..........................................................................................................................................8
Control..................................................................................................................................................................................................9
Direct Displacement Control.................................................................................................................................................. 9Control Handle Requirements ...............................................................................................................................................9
Operating Parameters
Overview........................................................................................................................................................................................... 10
Input / Output Speed....................................................................................................................................................................10
System Pressure..............................................................................................................................................................................10
Input Power......................................................................................................................................................................................10
Charge Pressure..............................................................................................................................................................................10
Case pressure...................................................................................................................................................................................11
Viscosity.............................................................................................................................................................................................11
Temperature.................................................................................................................................................................................... 11
System Design Parameters
Filtration System ............................................................................................................................................................................12
Filtration............................................................................................................................................................................................ 13
Charge Filtration....................................................................................................................................................................... 13
Suction Filtration.......................................................................................................................................................................13
Independent Braking System.................................................................................................................................................... 14
Fluid Selection.................................................................................................................................................................................14
Reservoir............................................................................................................................................................................................14
Case Drain.........................................................................................................................................................................................14
Charge Pump...................................................................................................................................................................................15
Bearing Loads and Life.................................................................................................................................................................15
Applications with External Shaft Loads............................................................................................................................ 15
Input Shaft...................................................................................................................................................................................16
Shaft Torque Rating and Spline Lubrication...................................................................................................................17
Shaft Availability....................................................................................................................................................................... 17
Sizing Equations............................................................................................................................................................................. 18
Model CodeModel Code: A - H.......................................................................................................................................................................... 19
Model Code: J - M...........................................................................................................................................................................20
Model Code: N - Z...........................................................................................................................................................................21
Installation Drawings
Shaft Availability and Torque Ratings: Input Shaft/PTO Shaft.......................................................................................22
Shaft Availability and Torque Ratings: Output Shaft........................................................................................................ 23
Installation Drawings LDU20/24...............................................................................................................................................24Center section: Option A............................................................................................................................................................. 26
Center section: Option B............................................................................................................................................................. 27
Center section: Option F..............................................................................................................................................................28
Center section: Option H.............................................................................................................................................................29© Danfoss | March 2024

BC152886483777en-000304 | 3

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
General Description

Basic Design
LDU 20/24 is a U-style hydrostatic transmission with Z-shaft configuration, including a closed circuit
variable displacement piston pump with DDC (direct displacement control) and a fixed motor. LDU 20/24
is specially designed with optimized performance, size, and cost, in order to fulfill the demand of themobile applications marketplace. This document provides the detailed specifications and features for
LDU 20/24.
Key Features

•
•
•
•
•
•
•
•
•
•
•

Easy to use design as a complete hydrostatic transmission package for turf care machines & Compact
Utility Tractors up to 26 kw [35 PS]
Compact design
Single housing with Z-shaft configuration
Requires external charge flow
Bypass valve to allow the vehicle to be towed
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, utilizing female piston and male slipper design; overall efficiency ofapproximately 80% is possible
Improved kit life, higher duty cycle capability while providing the most compact design in this class ofhydrostatic transmission
Low trunnion operating force
Serviced by Danfoss' global network

Typical Applications•

Compact utility tractor

Schematic diagram
L3

M3

MA1

MA2

MB1

MB2

L1

4 | © Danfoss | March 2024

S

L2

P400004

BC152886483777en-000304

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Technical Specification

Physical properties
Features
Displacement

Units
Pump side1
Motor side

Recommended charge pump displacement for external charge supply
Torque at maximum displacement (theoretical)
Mass moment of inertia ofrotating components

Pump side
Motor side

Weight dry
Oil volume

cm3/rev [in3/rev]

LDU20

LDU24

0-20 [0-1.22]

0-24 [0-1.46]

20 [1.22]

N•m/bar [lbf•in/1000 psi]

6 [0.37]
0.32 [195.2]

With passage

0.38 [234.2]

0.000936 [0.000693]

kg•m2 [slug•ft2]

0.000928 [0.000683]

kg [lb]Case only

24 [1.46]

cm3/rev [in3/rev]

14.1 [31.1]
1.1 [0.28]

liter [US gal]

1.2 [0.32]

Installation

See Installation Drawings on page 25-30

Rotation

Clockwise or Counterclockwise

Ports (ISO 11926-1)

See Installation Drawings on page 25-30

Input shafts and PTO shafts

See Installation Drawings on page 23

Output shaft

See Installation Drawings on page 24

Control type

DDC

1 Max Swash angle is 18 deg.

Operation Parameters
Features

Input speed

Units

LDU20

Minimum for external charge supply

500

Minimum for full performance

1300

Rated

min-1 (rpm)3400

Maximum
System pressure

Maximum working pressure
Maximum pressure

3800

Maximum

kw [PS]

Charge pressure

Minimumbar [psi]© Danfoss | March 2024

Rated
Maximum

300 [4350]

bar [psi]

Input power

Case pressure

LDU24

bar [psi]

345 [500]
22 [30]26 [35]
5 [73]
1 [14.5]
3 [43.5]

BC152886483777en-000304 | 5

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Technical Specification
Fluid Specifications
Features

Units
Minimum

Viscosity

Recommended range

7 [49]
mm2/sec. [ SUS]

Maximum

Recommended range-40 [-40]
Degrees C [Degrees F]

Maximum

22/18/13

Efficiency (charge pressure filtration)
Efficiency (suction and return line
filtration)
Recommended inlet screen meshsize

6 | © Danfoss | March 2024

+82 [+180]+104 [+220]

Cleanliness per ISO 4406
Filtration(recommended minimum)

12-60 [66-280]
1600 [7500]

Minimum
Temperature

LDU20/24

β15-20=75(β10≥10)β-ratioµm

β15-20=75(β10≥10)100-125

BC152886483777en-000304

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Operations

Check / High Pressure Relief ValveLDU 20/24 is equipped with a combination high pressure relief and charge check valve. The highpressure relief function is a dissipative (with heat generation) pressure control valve for the purpose oflimiting 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 thevalve, 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, LDU 20/24 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 easieradjustment of the vehicle linkage for machine neutral. The orifice connects the working loop, which is amain 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 toincrease downhill creep. It is recommended to install the orifice in a specific working loop, which ispressurized when the vehicle moves in reverse.
The HPRV are set at the following flow rates
Check/HPRV without orifice

5 l/min [1.3 US gal/min]

Check/HPRV with orifice

17 l/min [4.5 US gal/min]

P400005

C Caution
HPRVs are factory set at a low flow condition. Any application or operating condition which leads toelevated 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.

© Danfoss | March 2024

BC152886483777en-000304 | 7

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Operations
Bypass Function
The LDU20/24 contains a dedicated bypass valve option. The bypass function is activated when thebypass valve is mechanically backed out 3 full turns (maximum). The bypass function allows a machine orload to be moved without rotating the pump shaft or prime mover. In some applications, it is desirable tobypass the fluid around the variable displacement pump when pump shaft rotation is unachievable orundesired. To illustrate, an inoperable vehicle may need to be moved to the service or the repair location,or winched onto a trailer without operating the prime mover. Thus, LDU20/24 is designed with thebypass function as an option.
Bypass Function

Bypass Valve
System Pressure

System Pressure
P400006

C Caution
Excessive speed or extended movement will damage the transmission.
Avoid excessive speeds and extended load/vehicle movement. Do not move the load or vehicle morethan 20 % of maximum speed or for longer than 3 minutes. When the bypass function is no longer
needed, reseat the bypass valve to the normal operating position.

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 HSTcase 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 pump.
Charge Pressure Relief Valve settings for external charge supply
Flow, l/min [US gal/min]
LDU 20/24

10.8 [2.9]Charge Pressure Relief Valve Function

Charge Flow

P4000078 | © Danfoss | March 2024

BC152886483777en-000304

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Operations
Control
Direct Displacement Control
The LDU 20/24 features direct displacement control (DDC).The swashplate angle is set directly by acontrol lever or linkage attached directly to the swashplate trunnion. Control lever movement changes
the speed and rotating direction of the motor by increasing or decreasing the swashplate angle.
Control Handle Requirements
Maximum allowable trunnion torque is 79.1 N•m [700 lbf•in]. The approximate torque necessary to rotate
the control arm at 300 bar system operating pressure and 3000 rpm is 25 N•m with the standard
valveplate. Minimum torque necessary to hold the swashplate at a zero angle for neutral is 2.3 N•m [20in•lbf ]. The actual value will vary due to the influence of pump operating conditions. For mating
dimensions, see Installation Drawings LDU20/24 on page 24.
Input shaft rotation

CW

Trunnion location

CCW

Right

Left

Right

Left

Trunnion rotation

CW

CCW

CW

CCW

CW

CCW

CW

CCW

Output rotation

CCW

CW

CW

CCW

CW

CCW

CCW

CW

High pressure port

MA

MB

MB

MA

MB

MA

MA

MB

Low pressure port

MB

MA

MA

MB

MA

MB

MB

MA

W WarningWith no external forces applied to the swashplate trunnion, internal hydraulic forces may not return theswashplate to the neutral position under all conditions of operation.

© Danfoss | March 2024

BC152886483777en-000304 | 9

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Operating Parameters
Overview
This section defines the operating parameters and limitations for LDU 20/24 with regard to input speeds
and pressures. For actual parameter data, refer to the operating parameters table in the Technical
Specifications section.
Input / Output Speed
Minimum speed is the lowest input speed recommended during engine idle condition. Operating below
minimum speed limits pump’s ability to maintain adequate flow for lubrication and power transmission.
Rated speed is the highest input speed recommended at full power condition. Operating at or below
this speed should yield satisfactory product life.
Maximum speed is the highest operating speed permitted. Exceeding maximum speed reduces productlife and can cause loss of hydrostatic power and braking capacity. Never exceed the maximum speed
limit under any operating conditions.
Operating conditions between rated speed and maximum speed should be restricted to less than fullpower and to limited periods of time. For most drive systems, maximum unit speed occurs during
downhill braking or negative power conditions.

W Warning
Unintended vehicle or machine movement hazard.
Exceeding maximum speed may cause a loss of hydrostatic drive line power and braking capacity. An
independent braking system is required, redundant to the hydrostatic transmission, which is sufficient tostop and hold the vehicle or machine under all conditions of operation in the event of hydrostatic drive
power loss.

System Pressure
System pressure is the differential pressure measured between the gage ports Ma and Mb. It is thedominant operating variable affecting hydraulic unit life. High system pressure, which results from highload, reduces expected life. Hydraulic unit fatigue life depends on speed and normal operating—or
weighted average—pressure that you can only determine from a duty cycle analysis.
Maximum Working Pressure is the highest recommended application pressure. Maximum working
pressure is not intended to be a continuous pressure. Propel systems with application pressures at, or
below, this pressure should yield satisfactory unit life given proper component sizing.
Maximum pressure (peak) is the highest intermittent pressure allowed under any circumstances.
Applications with applied pressures between maximum working and maximum intermittent require
factory approval with complete application, duty cycle, and life expectancy analysis.
All pressure limits are differential pressures referenced to low loop (charge) pressure. Subtract low looppressure from gauge readings to compute the differential.

Input Power
Maximum continuous input power is the highest recommended input power to HST excluding PTO
output power.
Charge Pressure
An internal charge relief valve regulates charge pressure. Charge pressure maintains a minimum pressurein the low side of the transmission loop. Charge pressure is the differential pressure above case pressure.
Minimum charge pressure is the lowest pressure safe working conditions allow in the system.

10 | © Danfoss | March 2024

BC152886483777en-000304

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Operating Parameters
Case pressure
Under normal operating conditions, the rated case pressure must not be exceeded. During cold start casepressure must be kept below maximum intermittent case pressure. Size drain plumbing accordingly.

C Caution
Possible component damage or leakage
Operation with case pressure in excess of stated limits may damage seals, gaskets, and/or housings,
causing external leakage. Performance may also be affected since charge and system pressure are
additive to case pressure.

Viscosity
Maintain fluid viscosity within the recommended range for maximum efficiency and bearing life.
Minimum viscosity should only occur during brief occasions of maximum ambient temperature andsevere duty cycle operation. Maximum viscosity should only occur at cold start. Limit speeds until thesystem warms up. Refer to the fluid specifications table.
Temperature
1. Maintain fluid temperature within the limits shown in the Technical Specification section.
Minimum temperature relates to the physical properties of the component materials. Cold oil may
affect the ability of the transmission to provide flow and transmit power.
Continuous temperature should not be exceeded for longer than 2 minutes (single event) or for
more than 2% of the application duty cycle. Operating the unit at or below continuous temperature
should yield satisfactory unit life. The application's cooling system shall be designed to maintain theoil temperature below the continuous temperature limit.
Maximum intermittent temperature: is based on material properties. Don’t exceed it.
2. Measure maximum temperature at the hottest point in the system.
Refer to the fluid specifications table for data.
3. Ensure fluid temperature and viscosity limits are concurrently satisfied.

© Danfoss | March 2024

BC152886483777en-000304 | 11

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
System Design Parameters
Filtration System
To prevent premature wear, ensure that only clean fluid enters the hydrostatic transmission circuit. A
filter capable of controlling the fluid cleanliness to ISO 4406, class 22/18/13 (SAE J1165) or better, undernormal operating conditions, is recommended. These cleanliness levels cannot be applied for hydraulicfluid residing in the component housing/case or any other cavity after transport.
Filtration strategies include suction or pressure filtration. The selection of a filter depends on a number offactors including the contaminant ingression rate, the generation of contaminants in the system, therequired fluid cleanliness, and the desired maintenance interval. Filters are selected to meet the above
requirements using rating parameters of efficiency and capacity.
Filter efficiency can be measured with a Beta ratio1 (βX). For simple suction-filtered closed circuit
transmissions and open circuit transmissions with return line filtration, a filter with a β-ratio within therange of β35-45 = 75 (β10 ≥ 2) or better has been found to be satisfactory. For some open circuit systems,
and closed circuits with cylinders being supplied from the same reservoir, a higher filter efficiency isrecommended. This also applies to systems with gears or clutches using a common reservoir. For thesesystems, a charge pressure or return filtration system with a filter β-ratio in the range of β15-20 = 75 (β10 ≥10) or better is typically required.
Because each system is unique, only a thorough testing and evaluation program can fully validate thefiltration system. Please see Design Guidelines for Hydraulic Fluid Cleanliness Technical Information,
BC152886482150 for more information.
Cleanliness level and βx-ratio
Filtration(recommended
minimum)

Cleanliness per ISO 4406

22/18/13

Efficiency (charge pressure filtration)

β15-20 = 75 (β10 ≥ 10)

Efficiency (suction and return line filtration) β35-45 = 75 (β10 ≥ 2)
Recommended inlet screen mesh size

1

100 – 125 µm

Filter βx-ratio is a measure of filter efficiency defined by ISO 4572. It is defined as the ratio of the number of particles greater than agiven diameter (“x” in microns) upstream of the filter to the number of these particles downstream of the filter.

12 | © Danfoss | March 2024

BC152886483777en-000304

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
System Design Parameters
Filtration
Charge Filtration
The pressure filter is remotely mounted in the circuit after the charge pump, as shown in theaccompanying illustration.
Filters used in charge pressure filtration circuits must be rated to at least 34.5 bar [500 psi] pressure.
Danfoss recommends locating a 100 - 125 µm screen in the reservoir or in the charge inlet line whenusing charge pressure filtration.
A filter bypass valve is necessary to prevent damage to the system. In the event of high pressure drop
associated with a blocked filter or cold start-up conditions, fluid will bypass the filter. Avoid working with
an open bypass for an extended period. We recommend a visual or electrical bypass indicator. Proper
filter maintenance is mandatory.
Charge filtration

Suction Filtration
The suction filter is placed in the circuit between the reservoir and the inlet to the charge pump as shownin the accompanying illustration.
Suction filtration

P400009© Danfoss | March 2024

BC152886483777en-000304 | 13

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
System Design Parameters
Independent Braking System
Vehicle propel applications may require a provision for non-linear control input to reduce control
sensitivity near neutral. Damping or frictional forces may be necessary to produce the desired control
feeling.
These units do not include any neutral centering device for the swashplate. It is necessary to provide aforce in the machine’s control system that will hold the swashplate at the desired angle. A “failsafe“ which will return the swashplate to the neutral in the event of linkage failure is recommended.
It is necessary for the application to have an independent braking system which is capable of stopping
the vehicle in all working conditions. In the event of control linkage or direct displacement control subsystem failure (trunnion shaft, bearings, carriers, etc.), the independent braking system must be capableof stopping the vehicle which may be operating at full hydrostatic load.

W Warning
Unintended vehicle or machine movement hazard.
The loss of hydrostatic drive line power, in any mode of operation (forward, neutral, or reverse) may cause
the system to lose hydrostatic braking capacity. An independent braking system is required, redundant
to the hydrostatic transmission, which is sufficient to stop and hold the vehicle or machine under all
conditions of operation in the event of hydrostatic drive power loss.

Fluid Selection
Ratings and performance data are based on operating with hydraulic fluids containing oxidation, rustand foam inhibitors. These fluids must possess good thermal and hydrolytic stability to prevent wear,
erosion, and corrosion of the components.

C Caution
Never mix hydraulic fluids of different types.

Reservoir
The hydrostatic system reservoir should accommodate maximum volume changes during all system
operating modes and promote de-aeration of the fluid as it passes through the tank.
A suggested minimum total reservoir volume is 5⁄8 of the maximum charge pump flow per minute with aminimum fluid volume equal to ½ of the maximum charge pump flow per minute. This allows 30 seconds
fluid dwell for removing entrained air at the maximum return flow. This is usually adequate to allow for aclosed reservoir (no breather) in most applications.
Locate the reservoir outlet (charge pump inlet) above the bottom of the reservoir to take advantage ofgravity separation and prevent large foreign particles from entering the charge inlet line. A 100-125 µm
screen over the outlet port is recommended.
Position the reservoir inlet (fluid return) to discharge below the normal fluid level, toward the interior of
the tank. A baffle (or baffles) will further promote de-aeration and reduce surging of the fluid.
Case Drain
A case drain line must be connected to one of the case outlets to return internal leakage to the system
reservoir. Use the higher of the outlets to promote complete filling of the case and ensure that the
housing remains full of oil at all times.
Since case drain fluid is typically the hottest fluid in the system, it is a good idea to return this flow to thereservoir via the heat exchanger

14 | © Danfoss | March 2024

BC152886483777en-000304

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
System Design Parameters
Charge Pump
Charge flow requirements for the LDU 20/24 should be equivalent to a 6-8cc/rev charge pump,depending on pump input speed. Charge flow must not exceed 30 l/min.
Bearing Loads and Life
Bearing life is a function of speed, system pressure, charge pressure, and swashplate angle, plus any
external side or thrust loads. The influence of swashplate angle includes displacement as well as
direction. External loads are found in applications where the pump is driven with a side/thrust load (beltor gear) as well as in installations with misalignment and improper concentricity between the pump anddrive coupling. All external side loads will act to reduce the normal bearing life of a pump. Other life
factors include oil type and viscosity.
Applications with External Shaft Loads
LDU 20/24 is designed with bearings that can accept external radial and, in some cases, axial (thrust)loads. When external loads are present, the allowable radial shaft loads are a function of the load position
relative to the housing surface, the load orientation relative to the internal loads, and the operatingpressures of the hydraulic unit. In applications where external shaft loads cannot be avoided, the impact
on bearing life can be minimized by proper orientation of the load. Pump orientation is also a
consideration to alleviate net loading on the shaft from the external load.
• In applications where the pump is operated such that nearly equal amounts of forward vs. reverse
swashplate operation is experienced; bearing life can be optimized by orientating the external sideload at 90° or 270° such that the external side load acts 90° to the rotating group load (for details see
drawing below).
• In applications where the pump is operated such that the swashplate is predominantly (> 75 %) on
one side of neutral (ie vibratory, conveyor, typical propel), bearing life can be optimized byorientating the external side load opposite of the internal rotating group load. The direction ofinternal loading is a function of rotation and which system port has flow out.
• LDU 20/24 is designed with bearings that can accept some thrust load such that incidental thrustloads are of no consequence. When thrust loads are anticipated the allowable load will depend on
many factors and it is recommended that an application review be conducted.
Contact Danfoss for a bearing life review if external side loads are present.
Thrust loads should be avoided. Contact your Danfoss representative to discuss applications where thrustloads are anticipated.

© Danfoss | March 2024

BC152886483777en-000304 | 15

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
System Design Parameters
Input Shaft
The maximum allowable radial load (Re) is based on the maximum external moment (Me) and the
distance (L) from the mounting flange to the load. It is shown in the chart below.
Re = Me / L
MeShaft moment

L

Flange distanceRe

External force to the shaft

L

0° Re

PTO shaft

Re
90° Re270° ReMe

Input shaft

Output shaft

180° Re
P400010

1200
1000

Re N

800
600
400
200

0

10

20

30

40

50

distance (L) mm
P400011

Danfoss recommends clamp-type couplings for applications with radial shaft loads
Contact your Danfoss representative for an evaluation of unit bearing life if you have continuously
applied external loads exceeding 25 % of the maximum allowable radial load (Re) or the pumpswashplate is positioned on one side of center all or most of the time.

PTO shaft, Output shaft
Avoid any load in either direction.

16 | © Danfoss | March 2024

BC152886483777en-000304

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
System Design Parameters
Shaft Torque Rating and Spline Lubrication
Maximum torque ratings are based on torsional fatigue strength considering 100,000 full load reversing
cycles. However, a spline running in an oil-flooded environment provides superior protection fromoxygen in addition to contaminant flushing. The rated torque of a flooded spline can increase to that of
the maximum published rating. A flooded spline would be indicative of a pump driven by a pump driveor plugged into an auxiliary pad of a pump.
Maintaining a spline engagement at least equal to the pitch diameter will also maximize spline life. Spline
engagements of less than ¾ pitch diameter are subject to high contact stress and spline fretting.
Shaft Availability
Alignment between the mating spline’s pitch diameters is another critical factor in determining theoperating life of a splined drive connection. Plug-in, or rigid spline drive installations can impose severeradial loads on the shaft. The radial load is a function of the transmitted torque and shaft eccentricity.
Increased spline clearance will not totally alleviate this condition, but increased spline clearance will
prevent mechanical interference due to misalignment or radial eccentricity between the pitch diametersof the mating splines. Maximize spline life by adding an intermediate coupling between the bearing
supported splined shafts.

© Danfoss | March 2024

BC152886483777en-000304 | 17

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
System Design Parameters
Sizing Equations
The following equations are helpful when sizing hydraulic transmissions. Generally, the sizing process is
initiated by an evaluation of the machine system to determine the required transmission speed andtorque to perform the necessary work function. Refer to Selection of drive line components,
BC157786484430, for a more complete description of hydrostatic drive line sizing.
Based on SI units

Based on US units

Input torqueNm[lbf•in]

Input power

kW

[hp]

OutputtorqueNm[lbf•in]

Output
power

kW

[hp]

Where;

18 | © Danfoss | March 2024

Vgp

Pump displacement per rev. cm3 [in3]Vgm

Motor displacement per rev. cm3 [in3]Δp

pHD – pND bar [psi]ηmp

Pump Mechanical-hydraulic (Torque) efficiency

ηmm

Motor Mechanical-hydraulic (Torque) efficiency

ηtp

Pump Overall efficiency

ηtm

Motor Overall efficiency

pHD

High pressure bar [psi]pND

Low pressure bar [psi]npInput speednm

Output speed

BC152886483777en-000304

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Model CodeModel Code: A - H

A - Displacement
Code

Description

20D

Displacement: 20 cc/rev / Block type : standard Block24D

Displacement: 24 cc/rev / Block type : standard Block

B - Rotation
Code

Description

L

Left hand side viewing from input shaft (CCW)R

Right hand side viewing from input shaft (CW)C - Valve Plate
Code

Description

A

Standard

D - Control Arm Position
Code

Description

L

Left hand side viewing from input shaft (pump located upside)R

Right hand side viewing from input shaft (pump located upside)

E - Control Arm Configuration
Code

Description

S

SquareF - Pump Shaft Configuration (Input Shaft/PTO Shaft)
Code

Description

JJ

JIS 14T (Input) / JIS 14T (PTO)

AA

ANSI 16/32-13T (Input) / ANSI 16/32-13T (PTO)

H - Output Shaft Configuration)© Danfoss | March 2024

Code

Description

J

JIS 14TA

ANSI 16/32-13T

BC152886483777en-000304 | 19

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Model CodeModel Code: J - M

J - Centersection Configuration
Code

Description
Drain port: 9.8mm on centersection (A)Charge port : 9.8mm on centersection(A)Drain port: 3/4-16 drain port on housing
Charge port : 9/16-18 on centersection

Without Bypass valve

Without Bypass valve

A

With Bypass valve on left
valve

With Bypass valve on left
side

X

B

X

F

X

H

X

(A) Connect charge inlet and drain line directly from LDU20 centersection with trans axle. See Installation Drawings

on page 27-30 for detail.

K - Charge Pump Displacement
Code

Description

N

None

L - Charge Relief Setting
Code

Description

07

7 bar at 10.8 l/min [102 psi at 2.9 US gal/min]

M - Bypass ValveCode

20 | © Danfoss | March 2024

Description

N

None

C

w/Bypass Valve Left hand side

BC152886483777en-000304

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Model CodeModel Code: N - Z

N - Check & Relief Valve Side A
P - Check & Relief Valve Side B
The following two tables are used to selection for ports “A” and “B”(Orifice must not be used for both side (A or B))**N

Check & Relief valve without orifice

14N

140 bar [2030 psi]

17N

175 bar [2538 psi]

21N

210 bar [3045 psi]

23N

230 bar [3285 psi]

25N

250 bar [3625 psi]

28N

280 bar [4060 psi]

30N

300 bar [4351 psi]

32N1

325 bar [4713 psi]

34N1

345 bar [5003 psi]

00N

Poppet type check valve

1 Duty cycle analysis and Factory approval is needed. See Maximum Pressure in System Pressure on page 10.

**A

Check & Relief valve with orifice (∅0.85)

14A

140 bar [2030 psi]

17A

175 bar [2538 psi]

21A

210 bar [3045 psi]Y - Special Hardware Features
Code

Description

NNN

Housing Configuration : Standard

Z - Paint and Tag© Danfoss | March 2024

Code

Description

NNN

No Paint (corrosion protection), Danfoss Logo

NAN

No Paint (corrosion protection), Daikin Logo

BNN

Black Paint, Danfoss Logo

BAN

Black Paint, Daikin Logo

BC152886483777en-000304 | 21

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Installation Drawings
Shaft Availability and Torque Ratings: Input Shaft/PTO Shaft
Input shaft/PTO Shaft
SplineTorque RatingN•m [lbf•in]
Rated Torque

JJ

Maximum Torque

14 teeth, 1.25 module (Input)

122 [1080]

314 [2779]

14 teeth, 1.25 module (PTO)

89 [788]

310 [2743]±1

212 ±1[1.339 ±0.039 ][8.346 ±0.039 ]34

30 ±0.5 full spline length

22 ±0.5 full spline length[1.181 ±0.02 ]0∅19.75 -0.15

0[0.778 -0.006]

0∅ 19.75 -0.15[0.866 ±0.02 ]Spline data
Number of teeth : 14
Module: 1.25Pressure angle : 20°
Pitch diameter : 17.5
Addendum modification
Coefficient: 0.8
Involute spline
Per: JIS D 2001 CLASS a

0[0.778 -0.006]

OptionSpline data
Number of teeth : 14
Module: 1.25Pressure angle : 20°
Pitch diameter : 17.5
Addendum modification
Coefficient: 0.8
Involute spline
Per: JIS D 2001 CLASS a
P400012

OptionSplineTorque RatingN•m [lbf•in]
Rated TorqueMaximum TorqueAA

13 theeth, 16/32 pitch (Input)

106 [938]

245 [2168]

13 theeth, 16/32 pitch (PTO)

106 [938]

226 [2000]±133[1.299 ±0.039 ]±0.5 full spline length20

20 ±0.5 full spline length

Spline data
Number of teeth : 13
Pitch fraction: 16/32
Pressure angle : 30°
Pitch diameter : 20.638 [0.8125]
Type of fit: Fillet root sidePer
: ANSI B92.1-1970 CLASS
5[0.855 ±0.0035 ]∅21.72 ±0.09[0.787 ±0.02 ][0.855 ±0.0035 ]∅21.72 ±0.09[0.787 ±0.02 ]201 ±1[7.913 ±0.039 ]Spline data
Number of teeth : 13
Pitch fraction: 16/32
Pressure angle : 30°
Pitch diameter : 20.638 [0.8125]
Type of fit: Fillet root sidePer
: ANSI B92.1-1970 CLASS
5

P400013

22 | © Danfoss | March 2024

BC152886483777en-000304

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Installation Drawings
Shaft Availability and Torque Ratings: Output Shaft
Output Shaft
OptionJ

SplineTorque RatingN•m [lbf•in]

14 teeth, 1.25 module

Rated TorqueMaximum Torque87 [770]

310 [2743]

0[0.778 -0.006]

0∅19.75 -0.15

Spline data
Number of teeth : 14
Module: 1.25Pressure angle : 20°
Pitch diameter : 17.5
Addendum modification
Coefficient: 0.8
Involute spline
Per: JIS D 2001 CLASS a

21.5 ±0.5 full spline length[0.846 ±0.02 ]37 ±1
P400014[1.457 ±0.039 ]OptionSplineTorque RatingN•m [lbf•in]
Rated TorqueMaximum TorqueA

13 teeth, 20mm pitch

106 [938]

226 [2000][0.855 ±0.0035 ]∅21.72 ±0.09

Spline data
Number of teeth : 13
Pitch fraction: 16/32
Pressure angle : 30°
Pitch diameter : 20.638 [0.8125]
Type of fit: Fillet root sidePer
: ANSI B92.1-1970 CLASS
520 ±0.5 full spline length[0.787 ±0.02 ]36 ±1[1.417 ±0.039 ]© Danfoss | March 2024

P400015

BC152886483777en-000304 | 23

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Installation Drawings
Installation Drawings LDU20/24

20[ 0.787 ]14[0.551 ]27[ 1.063 ]27[ 1.063 ]108.7 Max[ 4.280 ]System A gage port "MA1"
Port ISO 11926-1, 3/4-16

Charge gage (inlet) port "M3"

[ 0.965 ±0.008 ]10 ±0.25[ 0.394 ±0.001 ]24.5 ±0.2

Port ISO 11926-1, 9/16-18
System B gage port "MB1"
Port ISO 11926-1, 3/4-16

R5 ±0.13[ R0.2 ±0.005 ]∅16 ±0.08[ 0.63 ±0.003 ]∅19.5 ±0.08[ 0.768 ±0.003 ]M8x1.25 Thread
16 [0.63] Min thread depth

166.52 Max[ 6.556 ]149.6[5.89 ]

DISP. 18° MAX DISP.
18° MAX
CCW
CW

Case drain port "L2"
Port ISO 11926-1, 3/4-16

R15[ 0.381 ]Control Arm Location (R)57.5[ 2.264 ]Charge inlet port "S"∅9.8 ±0.1 [0.386 ±0.004 ]46

46 ±0.05[ 1.811 ][ 1.811±0.002]

High pressure+0.036∅10 0

relief valve B[ 0.937 ±0.016 ]+0.0014[ 0.394 0]

102.8 ±0.05

CW

.06 4
+0 0.024 ]7 - 0.00 016
+ .0
9 -0
.66

[0

1
2X

5 0 +0.4
163.52 Max[ 6.438 ]40[ 1.016 ]86.2 Max[ 3.394 ]95.2 Max[3.748 ]86.2 Max[ 3.394 ]95.2 Max[3.748 ][ 0.197 +0.016 ]0∅90[ 2.286 ]Input shaft rotation

P400016CW

CCW

Trunnion location

24 | © Danfoss | March 2024

[4.047 ±0.002 ]85 ±0.07

102.8[ 4.047 ]CCW

69.15 Max[ 2.722 ]55 +0.046
05°[ 2.165 +0.0018
]
0

R11.5
[ 0.292 ][ 3.346 ±0.0028 ]

167.65 Max[ 6.600 ][0.433 ±0.004 ]122[ 4.803 ]42[ 1.654 ]Depth 11 ±0.1

4X 4

[ 0.937 ±0.016 ]23.8 ±0.4∅9.8 ±0.1 [0.386 ±0.004 ]See Model Code (Page 22)

M10X1.5 Thread
18 [0.71] Min
Thread depth
X4

23.8 ±0.4

Case drain port "L3"95.6
[ 3.764 ]Right

Trunnion rotation

CW

CCW

CW

CCW

Output rotation

CCW

CW

CW

CCW

High pressure port

MA

MB

MB

MA

Low pressure port

MB

MA

MA

MB

BC152886483777en-000304

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Installation Drawings

84.6[ 3.3]

Case drain port "L1"
Port ISO 11926-1, 3/4-16

0.8[ 0.03 ]57.5[ 2.264]

High pressure
relief valve A
Control Arm Location (R)42[1.654 ]See Model Code (Page 22)CW

25 ±0.2[ 0.984 ±0.008 ]49 ±0.2
Approx.
center ofgravity[ 1.929 ±0.008 ]29.9[ 1.2 ]

CCW

+0.38

4X ∅11 -0.05[0.433 +0.015-0.002 ]71 ±0.2[ 2.795 ±0.008 ]80 ±0.2[ 3.15 ±0.008 ]71 ±0.2[ 2.795 ±0.008 ]80 ±0.2[ 3.15 ±0.008 ]27[ 1.063 ]27[ 1.063 ]System A gage port "MA2"Port ISO 11926-1, 3/4-16

System B gage port "MB2"
Port ISO 11926-1, 3/4-16
20[ 0.787]© Danfoss | March 2024

P400017

BC152886483777en-000304 | 25

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Installation Drawings
Center section: Option A
Drain port: 9.8mm on centersection
Charge port: 9.8mm on centersection

Charge gage (inlet) port "M3"
Port ISO 11926-1, 9/16-18

Charge inlet port "S"∅9.8 ±0.1 [0.386 ±0.004 ]Case drain port "L1, L2"
Case drain port "L3"

Port ISO 11926-1, 3/4-16∅9.8 ±0.1 [0.386 ±0.004 ]

L3

M3

MA1

MA2

MB1

MB2

L1

26 | © Danfoss | March 2024

S

L2

P400018

BC152886483777en-000304

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Installation Drawings
Center section: Option B
Drain port: 3/4-16 on Housing.
Charge port: 9/16-18 on centersection
Charge inlet port "M3"72.5

[ 2.854 ]72.5[ 2.854 ]Port ISO 11926-1, 9/16-18

Case drain port "L1, L2"

77.4[3.047 ]Port ISO 11926-1, 3/4-16

M3

MA1

MA2

MB1

MB2

L1

© Danfoss | March 2024

L2

P400019

BC152886483777en-000304 | 27

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Installation Drawings
Center section: Option F
Drain port: 9.8mm on centersection
Charge port: 9.8mm on centersection With Bypass valve

Charge inlet port "S"∅9.8 ±0.1 [ 0.386 ±0.004 ]Case drain port "L1, L2"

Case drain port "L3"

Port ISO 11926-1, 3/4-16

34[1.339]∅9.8 ±0.1 [ 0.386 ±0.004 ]Bypass valve(17mm external hex)
Torque 12 N•m [9 lbf•ft]

18[0.709]

L3

S

M3

MA1

MA2

MB1

MB2

L1

28 | © Danfoss | March 2024

L2

P400020

BC152886483777en-000304

Technical Information
LDU20/24 Closed Circuit Axial Piston Transmission
Installation Drawings
Center section: Option H
Drain port: 3/4-16 on Housing
Charge port: 9/16-18 on centersection With Bypass valve

Case drain port "L1, L2"

Charge inlet port "M3"

Port ISO 11926-1, 3/4-16

34[ 1.339 ]Port ISO 11926-1, 9/16-18

Bypass valve18[ 0.709 ]

M3

MA1

MA2

MB1

MB2

L1

© Danfoss | March 2024

L2

P400021

BC152886483777en-000304 | 29

Products we offer:

•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•
•

Cartridge valves
DCV directional control
valvesElectric converters
Electric machines

Danfoss Power Solutions is a global manufacturer and supplier of high-quality hydraulic andelectric components. We specialize in providing state-of-the-art technology and solutions
that excel in the harsh operating conditions of the mobile off-highway market as well as themarine sector. Building on our extensive applications expertise, we work closely with you toensure exceptional performance for a broad range of applications. We help you and othercustomers around the world speed up system development, reduce costs and bring vehicles
and vessels to market faster.

Gear motors

Danfoss Power Solutions – your strongest partner in mobile hydraulics and mobile
electrification.

Gear pumps

Go to www.danfoss.com for further product information.

Hydraulic integrated
circuits (HICs)
Hydrostatic motors

We offer you expert worldwide support for ensuring the best possible solutions foroutstanding performance. And with an extensive network of Global Service Partners, we also
provide you with comprehensive global service for all of our components.

Electric motors

Hydrostatic pumps
Orbital motors
PLUS+1® controllers
PLUS+1® displays
PLUS+1® joysticks andpedals
PLUS+1® operator
interfaces
PLUS+1® sensors
PLUS+1® software
PLUS+1® software services,support and training
Position controls andsensors
PVG proportional valves
Steering components andsystems
Telematics

Local address:

Hydro-Gear
www.hydro-gear.com
Daikin-Sauer-Danfoss
www.daikin-sauer-danfoss.com

Danfoss
Power Solutions (US) Company
2800 East 13th Street
Ames, IA 50010, USA
Phone: +1 515 239 6000

Danfoss
Power Solutions GmbH & Co. OHG
Krokamp 35
D-24539 Neumünster, Germany
Phone: +49 4321 871 0

Danfoss
Power Solutions ApS
Nordborgvej 81
DK-6430 Nordborg, Denmark
Phone: +45 7488 2222

Danfoss
Power Solutions Trading(Shanghai) Co., Ltd.
Building #22, No. 1000 Jin Hai Rd
Jin Qiao, Pudong New District
Shanghai, China 201206
Phone: +86 21 2080 6201

Danfoss can accept no responsibility for possible errors in catalogues, brochures and other printed material. Danfoss reserves the right to alter its products without notice. This also applies to products
already on order provided that such alterations can be made without subsequent changes being necessary in specifications already agreed.
All trademarks in this material are property of the respective companies. Danfoss and the Danfoss logotype are trademarks of Danfoss A/S. All rights reserved.

© Danfoss | March 2024

BC152886483777en-000304