Technical Information

BDU Series
Hydrostatic Transmissions

www.danfoss.com

Technical Information
BDU Series Hydrostatic Transmissions

Revision history

Table of revisionsDate

2 | © Danfoss | November 2022

ChangedRev

November 2022 Added caution for packing and transportation

0208

November 2021 Removed contents of BDP, and aligned revision number along with DAM Hub.

0207

November 2020 Minor update in Hydraulic Fluid, and changed document number from 'BC00000025' and'520L0935' to 'BC152886484098'

0104

December 2018 Fixed Model Code "H"

0103

May 2017

Fixed typo

0102

June 2016

Convertd to DITA-CMS

0101

Mar 2010

Correction - Drawing

AC

Jan 2009

Correction - Text

AB

Jan 2006

First editionAA

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Contents
General Description
BDU Series Family.............................................................................................................................................................................5
Features and Benefits......................................................................................................................................................................5
Design...................................................................................................................................................................................................6
BDU-06/10S........................................................................................................................................................................................ 8
Pictorial Diagram.........................................................................................................................................................................8
System Schematic.......................................................................................................................................................................8
BDU-10L/21L/21H.............................................................................................................................................................................9
Pictorial Diagram.........................................................................................................................................................................9
System Schematic: BDU-21L................................................................................................................................................... 9
System Schematic: BDU-21H................................................................................................................................................10
Technical Specifications
Features and Options................................................................................................................................................................... 11
Operating Parameters.................................................................................................................................................................. 12
Fluid Specifications....................................................................................................................................................................... 12
Efficiency........................................................................................................................................................................................... 13
BDU-06S....................................................................................................................................................................................... 13
BDU-10S....................................................................................................................................................................................... 13
BDU-10L....................................................................................................................................................................................... 13
BDU-21L/21H..............................................................................................................................................................................14
Operating Parameters
Overview........................................................................................................................................................................................... 15
Input / Output Speed....................................................................................................................................................................15
System Pressure..............................................................................................................................................................................15
Charge Pressure..............................................................................................................................................................................15
Charge Inlet Pressure....................................................................................................................................................................15
Case Pressure...................................................................................................................................................................................16
Hydraulic Fluids.............................................................................................................................................................................. 16
Temperature and Viscosity.........................................................................................................................................................16
System Design Parameters
Fluid and Filtration........................................................................................................................................................................ 17
Reservoir............................................................................................................................................................................................17
Control Shaft Force........................................................................................................................................................................17
Independent Braking System.................................................................................................................................................... 17
Features and Options
Shaft Load.........................................................................................................................................................................................18
Shaft Options...................................................................................................................................................................................18
Shaft Options : BDU-06S/10S/10L............................................................................................................................................ 19
Shaft Options : BDU-21L/21H.................................................................................................................................................... 20
Bypass Valve.....................................................................................................................................................................................21
High Pressure Relief Valve (hprv) and Charge Check (Overpressure Protection)................................................... 21
Charge Check Valve with Orifice.............................................................................................................................................. 23
Charge Check with Orifice.......................................................................................................................................................... 24
Optional Integrated Reservoir...................................................................................................................................................25
Filter.................................................................................................................................................................................................... 25
Fan....................................................................................................................................................................................................... 26
Component Selection
Maximum System Pressure........................................................................................................................................................ 27
Input Power......................................................................................................................................................................................28
Unit Life..............................................................................................................................................................................................29
Model CodeBDU : Model Code (A - B - C - D - E).......................................................................................................................................... 31
BDU : Model Code (F - G)............................................................................................................................................................. 32
BDU : Model Code (H - J - K)........................................................................................................................................................33
Recommended Installation and Maintenance© Danfoss | November 2022

BC152886484098en-000208 | 3

Technical Information
BDU Series Hydrostatic Transmissions
Contents
Housing Installation...................................................................................................................................................................... 34
Shaft Installation.............................................................................................................................................................................34
Start Up Procedure........................................................................................................................................................................ 34
Operation..........................................................................................................................................................................................34
Maintenance.................................................................................................................................................................................... 34
Packing and Transportation.......................................................................................................................................................34
Installation Drawings
BDU-06S : Ports and Dimensions..............................................................................................................................................35
BDU-06S : Control Arm Location.............................................................................................................................................. 36
BDU-06S : Motor Shaft..................................................................................................................................................................36
BDU-10S/10L : Ports and Dimensions.....................................................................................................................................37
BDU-10S/10L : Control Arm Location..................................................................................................................................... 38
BDU-10S/10L : Motor Shaft.........................................................................................................................................................39
BDU-10S : Shaft Configuration.................................................................................................................................................. 40
BDU-10L : Shaft Configuration and Charge Pumps Displacement.............................................................................. 41
BDU-21L/21H : Ports and Dimensions.................................................................................................................................... 42
BDU-21L/21H : Control Arm Location.....................................................................................................................................43
BDU-21L/21H : Motor Shaft........................................................................................................................................................ 44
BDU-21L/21H : Shaft Configuration and Charge Pump Displacement...................................................................... 45
Optional Fan.................................................................................................................................................................................... 47

4 | © Danfoss | November 2022

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
General Description

BDU Series Family
The BDU transmission is a “ Z” style transmission with a variable displacement pump and a fixed
displacement motor. The variable displacement pump features a cradle swashplate with a direct
proportional displacement control. Reversing the direction of tilt of the swashplate reverses the flow of
oil from the pump and thus reverses the direction of the motor output rotation. The fixed displacement
motor uses a fixed swashplate. The pump and motor are of the axial piston design and utilize
sphericalnosed pistons which are held against a thrust bearing by internal compression springs. The fluid
supply for the BDU-10L/21L/21H transmission is contained in an external reservoir and passes throughan external filter prior to entering the transmission and feeding the fixed displacement gerotor charge
pump. Excess fluid in the charge circuit is discharged over the charge relief valve back to the charge
pump inlet. Constant flow across a small fixed orifice connecting the charge circuit to the transmission
housing supplements the cooling flow.
The BDU-06S/10S transmission has a self-contained fluid supply and an integral filter. The fluid is forced
through the filter by positive “head” on the fluid in the housing reservoir with an assist by the negative
pressure created in the pump pistons as they create a vacuum. Charge check valves in the center section
are used to control the makeup flow of fluid to the low pressure side of the loop. A spool type bypass
valve is utilized in the transmission to permit moving the vehicle over short distances at low speeds
without starting the engine.
Features and Benefits

•
•
•
•
•
•
•

© Danfoss | November 2022

A complete transmission family to meet the needs of small vehicle application.
3 Transmission Frame Sizes: 6, 10, 21
PTO Capability on “Z” Style Transmission
Cost Effective, Compact, Lightweight Design
Low NoiseHigh Efficiency
Worldwide Sales and Service

BC152886484098en-000208 | 5

Technical Information
BDU Series Hydrostatic Transmissions
General Description
DesignCross-Section (BDU-10S)

1

16
2

15

3
14

4

5
13
12
11

10
6
8

9

7
P400202

1. Tank

6 | © Danfoss | November 2022

7. Spool type bypass valve

13. Shaft seal

2. Built-in filter

8. Cylinder block14. Input shaft

3. Spring

9. Piston

15. Cooling fan

4. Center section

10. Thrust bearing

16. Cradle swash plate

5. Output shaft

11. Housing

6. Spring

12. Ball bearing

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
General Description
1

20

2

2

19

6

18

7

17

16

8
9
15

10

14

11

3

12

5

13

4
P400203© Danfoss | November 2022

1. Suction Circuit

8. Charge Relief

15. Ball Bearing

2. Working Loop

9. Charge Circuit

16. Shaft Seal

3. Charge Check Valve

10. Output Shaft

17. Input Shaft

4. Spool Type Bypass Valve

11. Center Section

18. Cradle Swash Plate

5. Center Section

12. Cylinder Block

19. Piston

6. Suction Port

13. Thrust Bearing

20. Spring

7. Charge Pump

14. Housing

BC152886484098en-000208 | 7

Technical Information
BDU Series Hydrostatic Transmissions
General Description
BDU-06/10S
Pictorial Diagram
BDU-06S, BDU-10S
Bypass
Valve

Input
Shaft

Variable
Swashplate

CylinderBlock
Assembly

Cylinder Block
Assembly

Check Valve

OutputShaft

Variable
Displacement
Pump

Fixed
Swashplate

Check Valve

Fixed
Displacement
Motor

BDU
Housing

Reservor

B uilt-In
Filter(BDU-10S)

Working Loop(high pressure)

Working Loop(low pressure)

Suction Line

Case Drain Fluid

System SchematicControl Shaft “b”

Ø0.7
1

Ø0.8
2

ø0.7

Control Shaft “a”
Hydraulic Circuit

1

3

ø0.8
2

3
P400205

1. Ball Check Valve, Option Code. : BB
2. Check Valve with Ø0.7 Orifice, Option Code : 07
3. Check Valve with Ø0.8 Orifice, Option Code : 08

8 | © Danfoss | November 2022

BC152886484098en-000208

P400204

Technical Information
BDU Series Hydrostatic Transmissions
General Description
BDU-10L/21L/21H
Pictorial Diagram
BDU-10L, BDU-21L, BDU-21H (part of pump)
BypassValve
CylinderBlock
Assembly

Input
Shaft
Variable
Swashplate

Variable
Displacement
Pump

Cooling
Orifice

Cylinder Block
Assembly

Check Valve

ChargePump

Fixed
Displacement
Motor

Check Valve

ChargeReliefValve

OutputShaft

Fixed
Swashplate

Reservor

FilterWorking Loop(high pressure)

Working Loop(low pressure)

Suction Line

Case Drain Fluid

P400206

System Schematic: BDU-21L

BDU-21L
Control Shaft “b”

Ø1.0

1

Ø1.2

2

3

Ø0.8

Control Shaft “a”
Suction Port

Drain Port

Ø1.0

Ø1.2

Hydraulic Circuit

1

2

3
P400207

1. Ball Check Valve, Option Code. : BB
2. Check Valve with Ø1.0 Orifice, Option Code : 10
3. Check Valve with Ø1.2 Orifice, Option Code : 12

© Danfoss | November 2022

BC152886484098en-000208 | 9Technical Information
BDU Series Hydrostatic Transmissions
General Description
System Schematic: BDU-21H
BDU-21H

20.6MPa

17.2MPa

13.7MPa

20.6MPa

20.6MPaø 0.85

ø 0.7
×2

Control Shaft “b”

1

2

3

4

5

Ø0.8
20.6MPa

17.2MPa

13.7MPa

20.6MPa

20.6MPa

Suction Port

Drain Port

ø 0.85

ø 0.7
×2

Control Shaft “a”
Hydraulic Circuit

1

2

3

4

5
P400208

1. Check Valve with Relief Valve, Option Code. : R0
2. Check Valve with Relief Valve, Option Code. : R1
3. Check Valve with Relief Valve, Option Code. : R2
4. Check Valve with Relief Valve and Ø0.7 Twin Orifice, Option Code. : RA
5. Check Valve with Relief Valve and Ø0.85 Orifice, Option Code. : RB

10 | © Danfoss | November 2022

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Technical Specifications

Features and Options
Product Type & Frame
Features

Pump

Motor

Unit
BDU-10S

BDU-10L

BDU-21L

BDU-21H

10[0.61]

10[0.61]

21[1.28]

21[1.28]

15

15

15

15

Displacement

cm3 [in3]

6[0.37]

Swashplate Angle

degree15

Control Shaft

degree

15

21

21

22

22

Displacement

cm3 [in3]

6[0.37]

10[0.61]

10[0.61]

21[1.28]

21[1.28]

Swashplate Angle

degree

15

15

15

15

15

NA

NA

1.9
[0.12]

2.1[0.13]

3.0[0.18]

3000

3000

3600

3600

3600

3200

3200

3800

3800

3800

cm3 [in3]

Charge Pump Displacement
Rated
Output Speed

BDU-06S

Maximum(intermittent)

min-1

Maximum Output Torque (Theoretical)

Nm [lbf•in]

9.8
[87]

23.4
[208]

23.4
[208]

49.2
[436]

72.1
[639]

Input Power (Maximum)

kW [ps]

1.1
[1.5]

2.2
[3.0]

3.7
[5.0]

7.4
[10.0]

11.0[15.0]

Weightkgf [lbs]

4
[9]

6.3
[14]

6.5
[14]

10
[22]

10
[22]

Control Torque Required to Stroke Pump
(Maximum)Nm [lbf•in]

8.8
[78]

19.6
[174]

19.6
[174]

22.5
[200]

24.5
[217]

Mounting

See Installation Drawings

Rotation

Clockwise or Counterclockwise

Suction/Oil Tank Port (SAE O-ring Boss)

7/8-14 UNF

7/16-20 UNF

9/16-18 UNF

Other ports

See Installation Drawings

Shaft

See Installation Drawings

Bypass Valve
Neutral Valve/OrificeHigh Pressure Relief Valve

OP

STD

STD

STD

STD

NA/NA

NA/OP

NA/OP

OP/OP

OP/OP

NA

NA

NA

NA

STD

Filtration

W/Obuilt-inExternal

Reservoir

Integrated

Integrated

External

450

550

550

Space for the oil in the housing

cm3

External (Option, Integrated)
External
700

700

SAE J1926-1 / ISO 11926-1© Danfoss | November 2022

BC152886484098en-000208 | 11

Technical Information
BDU Series Hydrostatic Transmissions
Technical Specifications
Operating Parameters
Product Type & Frame
Parameter

Unit
BDU-06S

BDU-10S

BDU-10L

BDU-21L

BDU-21H

Input Speed
Minimum
Rated

1000
min-1

Maximum

600
3000

3600

3200

3800

System Pressure
Maximum Working
Maximum

bar
[psi]

105
[1530]

150[2185]

150[2185]

175[2549]

210[3059]
210[3059]

245[3569]

Charge Pressure

bar
[psi]

NA

3 [44] - 5 [73]Charge Inlet Pressure

bar
[psi]

NA

0.8 [12] abs

Case Pressure
Rated
Maximum (Cold Start)

0.3 [4]bar[psi]

0.7 [10]

Fluid Specifications
Features

Units
Minimum

Viscosity

TemperatureContinuous

7 [49]
mm2/sec.
[ SUS]

12-60 [66-280]

Maximum

1600 [7500]

Minimum-10 [14]

Maximum Continuous
Maximum

12 | © Danfoss | November 2022

BD Series°C [°F]82 [180]
104 [219]

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Technical Specifications
Efficiency
Input speed: 3000 min-1, Oil temperature: 50 °C, Full Displacement
BDU-06S
Efficiency (ηv:Volumetric, ηm:Mechanial, ηt:Overall)
100
90

10
40% 45% 50% 55% 60% 65%

80

70%

60

Output Torque Nm

Efficiency %

70
50
40
30
20
10
0

3

5
Theoretical Output Torpue Nm

70%
65%

5

60%
55%

0

7

50%

45%

40%

1000
2000
Output Speed min -1

3000
P400210

BDU-10S
Efficiency (ηv:Volumetric, ηm:Mechanial, ηt:Overall)

50
40
30
20
10
0

5

9
11
13
Theoretical Output Torpue Nm

%
73

%
70

%

%

65

%

60

%

55

50

%

60

Output Torque Nm

Efficiency %

40

20

70

45

80

%

100
90

73%
70%

10

65%
60%

55%
40%

17

0

45%

50%

1000
2000
Output Speed min -1

3000
P400211

BDU-10L

Output Torque Nm© Danfoss | November 2022557
9 11 13 15 16 18
Theoretical Output Torpue Nm

20

22

%
73

%
70

%
65

%
60

%
55

45
%
50
%

40

20

Efficiency %

100
90
80
70
60
50
40
30
20
10
0

%

Efficiency (ηv:Volumetric, ηm:Mechanial, ηt:Overall)

73%
70%

10

65%
55%
40%

0

45%

1000
2000
Output Speed min -1

60%
50%

3000
P400212

BC152886484098en-000208 | 13

Technical Information
BDU Series Hydrostatic Transmissions
Technical Specifications
BDU-21L/21H
Efficiency (ηv:Volumetric, ηm:Mechanial, ηt:Overall)

14 | © Danfoss | November 2022

%

%

75

70

%

%
65

60

40
%
45
%
50
%
55
%

50

Output Torque Nm

40

Efficiency %

100
90
80
70
60
50
40
30
20
10
0

11

23

34

46

Theoretical Output Torpue Nm

57

65

75%

30

70%

20

65%

10

40%

0

45%

55%

60%

50%

1000
2000
Output Speed min -1

BC152886484098en-000208

3000
P400213

Technical Information
BDU Series Hydrostatic Transmissions
Operating Parameters

Overview
Maintain operating parameters within prescribed limits during all operating conditions. This section
defines operating limits given in the table Operating Parameters.
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 between system ports A & B. It is the dominant operating
variable affecting hydraulic unit life. High system pressure, which results from high load, 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.

Charge Pressure
The charge pressure setting listed in the technical specifications is based on the charge flow across the
charge pressure relief valve at fluid temperature at 50˚C [120˚F].
Charge Inlet Pressure
Charge pump inlet conditions must be controlled in order to achieve expected life and performance. A
continuous inlet vacuum of no less than 0.8 abs bar is recommended. Normal vacuums less than 0.7 abs
bar would indicate inadequate inlet design or stricted filter.

© Danfoss | November 2022

BC152886484098en-000208 | 15

Technical Information
BDU Series Hydrostatic Transmissions
Operating Parameters
Case Pressure
Under normal operating conditions, the maximum continuous case pressure must not exceed 0.3 bar(4PSI). Maximum allowable intermittent case pressure during cold start must not exceed 0.7 bar (10PSI).

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. This condition may also affect performance since charge and system pressure
are referenced to case pressure.

Hydraulic Fluids
Ratings and data are based on operating with hydraulic fluids containing inhibitors to prevent oxidation,
rust, and foam. These fluids must possess good thermal and hydrolytic stability to prevent wear, erosion,and corrosion of the internal components.

C Caution
Never mix hydraulic fluids of different types.

Temperature and Viscosity
Temperature and viscosity requirements must be concurrently satisfied. The data shown in the table Fluid
Specifications on page 12, assume petroleum-based fluids are used.
The high temperature limits apply at the hottest point in the transmission, which is normally the motor
case drain. The system should generally be run at or below the rated temperature. The maximum
temperature is based on material properties and should never be exceeded.
Cold oil will generally not affect the durability of the transmission components, but it may affect theability of oil to flow and transmit power; therefore temperatures should remain 16 °C [30 °F] above thepour point of the hydraulic fluid. The minimum temperature relates to the physical properties ofcomponent materials.
For maximum unit efficiency and bearing life the fluid viscosity should remain in the recommended
operating range. The minimum viscosity should be encountered only during brief occasions ofmaximum ambient temperature and severe duty cycle operation. The maximum viscosity should be
encountered only at cold start.
Heat exchangers should be sized to keep the fluid within these limits. Testing to verify that thesetemperature limits are not exceeded is recommended.

16 | © Danfoss | November 2022

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
System Design Parameters

Fluid and Filtration
To prevent premature wear, it is imperative that only clean fluid enters the hydrostatic transmission
circuit. Therefore an inlet filter better than β20=1.4 is required in the charge pump inlet line. This filter
should not have a bypass and should be changed regularly to ensure system reliability. The BD serieshydrostatic transmission requires system filtration capable of maintaining fluid cleanliness at ISO
4406-1999 class 22/18/15 or better.
Reservoir
The BDU-06S and BDU-10S are designed with optional integrated reservoir. A reservoir for BDU-10L larger
than the 2 liter tank size is recommended. A reservoir for BDU-21L/H larger than the 5 liter tank size isrecommended. The hoses or piping size is recommended to be larger than 3/8 inch normal tube OD.
Control Shaft Force
The BDU transmission is designed with direct displacement control (DDC). DDC can be located at eitherside of the housing. It provides a simple, positive method of control. Movement of the control shaft
causes a proportional swashplate movement, thus varying the pump’s displacement from full
displacement in one direction to full displacement in the opposite direction.
The approximate maximum control torque necessary to rotate the control shaft is shown in the table oftechnical specifications. A stopper to prevent over-stroke is required at the end of maximum angle ofcontrol shaft. The control shaft force should be kept at or below the force in the table below.
Product type & Frame
Features
Allowable maximum force for control shaft

Unit
Nm

BDU-06S

BDU-10S

BDU-21L

10

20

25

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 “ fail safe
“ which will return the swashplate to the neutral in the event of linkage failure is recommended.

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. You must provide a braking system, redundant to thehydrostatic transmission, sufficient to stop and hold the vehicle or machine in the event of hydrostatic
drive power loss.

© Danfoss | November 2022

BC152886484098en-000208 | 17

Technical Information
BDU Series Hydrostatic Transmissions
Features and Options

Shaft Load
The maximum allowable radial road of input shaft (Re) is based on the maximum external moment andthe distance from the housing surface to the input shaft. The limit of radial load of input shaft is shown
the figure below:
Re
Tin

Tout (No Load)
No LoadDistance (L)No LoadNo LoadP400215

The maximum shaft thrust in (Tin) of input shaft is 18% of allowable radial road (Re) of the input shaft.
The shaft thrust out (Tout) of the input shaft should be no load. The radial and thrust load of the output
shaft should be no load.
BDU-21L/21H
1400
1200
1000

BDU-10S/10L
Re N →

800

BDU-06S
Re N →Re N →

600
400
200
0

10

20

30

distance (L) mm →

600

800
600

400

400

200

200
0

10

20

30

40

distance (L) mm →

50

-10

0

10

20

30

40 50

distance (L) mm →P400216

Shaft Options
The BDU transmissions are available with a variety of straight key, JIS Spline, JIS Serration, SAE Spline
shaft for input shaft, PTO shaft and output shaft. Details are shown in the Installation Drawings on page35.

18 | © Danfoss | November 2022

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Features and Options
Shaft Options : BDU-06S/10S/10L

B

Shafts:A = Output Shaft
B = PTO Shaft
C = Input Shaft

C

A

P400217

Output Shaft Options
Output Shaft

Code

15 x 13 x 1.0

J13

20 x 18 x 1.0

K1832/64-16T

S16

BDU-06S

BDU-10S

BDU-10L

JIS Spline

SAE Spline

PTO Shaft / Input Shaft Options
PTO Shaft

Input Shaft

Code

BDU-06S

BDU-10S

BDU-10L

KA0
KB0
None

Straight-Keyed D =
15 D
mm
KB1

PB1

Straight d =12.7 mm d© Danfoss | November 2022

Straight-Keyed D =
15D
mm

PB3

BC152886484098en-000208 | 19

Technical Information
BDU Series Hydrostatic Transmissions
Features and Options
PTO Shaft / Input Shaft Options (continued)
PTO Shaft

Input Shaft

Code

BDU-06S

BDU-10S

BDU-10L

PB2

Straight-Keyed D =15Dmm

JIS Serration
12 x 23 x 0.5

PB4

This charge pump housing is applied only for BDU-10L.

Shaft Options : BDU-21L/21H

C

B

Shafts:A = Output Shaft
B = PTO Shaft
C = Input Shaft

A

P400355

Output Shaft Options
Output Shaft

Code

20 x 14 x 1.25

J14

20 x 18 x 1.0

J1832/64-22T

S22

BDU-21L

BDU-21HJIS Spline

SAE Spline

20 | © Danfoss | November 2022

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Features and Options
PTO Shaft / Input Shaft Options
PTO Shaft

Input Shaft

Code

BDU-21L

BDU-21HKC1Straight-Keyed D =

D
17 mm

None

KC2

PC1

JIS Spline
15 x 13 x 1.0

Straight-Keyed D =

17 mm
D

PC2

PC3

SAE Spline
32/64-16T

Straight-Keyed D =
17
D mm

PC5

Bypass Valve
In some applications, it is desirable to move the vehicle over short distances at low speed without
starting the engine. A bypass valve allows oil to be routed from one side of the pump/motor circuit to theother, thus allowing the motor to turn. The bypass valve must be fully closed during normal vehicle
operation. BDU series transmissions utilize a spool-type bypass valve. The bypass valve plunger must be
depressed manually to open the valve. This connects both sides of the main hydraulic circuit to the
housing case and allows fluid to circulate without rotating the pump, prime mover and motor. A springcloses this valve on the 6S, 10L and 10S transmissions, while charge pressure closes the valve on the 21L
and 21H transmissions.
High Pressure Relief Valve (hprv) and Charge Check (Overpressure Protection)
The BDU-21H transmission is available with a combination charge check and high pressure relief valve
assembly. High pressure relief valves are available in a range of settings as shown in the Model Code on
page 31. Individual port pressure settings may be specified. The high pressure relief valve settings are adifferential pressure (referenced to charge pressure).
Check and Relief Valve for BDU-21H
Option Code© Danfoss | November 2022

Pressure setting
bar [psi]

Orifice

R0

210

-

R1

175

-

R2

140

-

RA

210

0.7 Twin

RB

210

0.85

BC152886484098en-000208 | 21

Technical Information
BDU Series Hydrostatic Transmissions
Features and Options

1

2

6

3

5
4

P400219

1. Charge circuit
2. Check and relief valve
3. Working loop (Main hydraulic circuit
4. Bypass valve
5. Working loop (Main hydraulic circuit)
6. Check and relief valve

22 | © Danfoss | November 2022

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Features and Options
Charge Check Valve with Orifice
The BDU transmissions are equipped with charge check valves. In some applications, it is desirable to use
charge check valve with orifice for expanding null dead band, giving both the safety measure to preventthe vehicle movement in the neutral position of the control shaft and easy adjustment of neutral position
when connected to vehicle linkage. The orifice connects the working loop, which is a main hydrauliccircuit, to a charge circuit. It always allows some internal leakage to ensure the expanding null dead bandaround neutral position of control shaft. However, it decreases the volumetric efficiency, particularly athigh system pressure in the working loop. It is recommended to install the orifice in a specific working
loop, which is pressurized when the vehicle moves in reverse. The orifice diameter improves the nulldead band but decreases the volumetric efficiency. A cross section and characteristics are shown below.
The charge check valves with orifice are available in a range of orifice diameters as shown in the Model
Code on page 31.
Output Flowwith OrificeForward

ReverseControl Shaft Angle
DB-STD
DB-OR

Neutral-OR

Neutral-STD
P400220

Input Speed: 3000min-1, Oil Temp: 50 °C , No Load
Features
Deadband of Control Shaft Angle(DB-STD)

BDU-10S/10L/21L/21H

Unit

Without Orifice[degree]Approx. 0.1

BDU-10S/10L
Features
Deadband of Control Shaft Angle(DB-OR)© Danfoss | November 2022

Unit

[degree]

BDU-21L

BDU-21H

Orifice diameter [mm]
Ø 0.7

Ø 0.8

Ø 1.0

Ø 1.2

Ø 0.85

Ø 0.7 twin

Approx.
0.5

Approx.
0.7

Approx.
0.5

Approx.
0.7

Approx.
0.35

Approx.
0.5

BC152886484098en-000208 | 23

Technical Information
BDU Series Hydrostatic Transmissions
Features and Options
Charge Check with Orifice
BDU-10L Check Valve

BDU-10S Check Valve
Check Valve (Ball) without OrificeP400223

BDU-10S
BDU-10L

Check Valve with Orifice
Orifice

P400224
P400222

P400221Check Valve (Ball) without OrificeP400226

BDU-21L

Check Valve with Orifice
Orifice

P400227
P400225

Check & Relief without OrificeP400229

BDU-21HCheck & Relief with Orifice
Orifice

P400230
P400228

24 | © Danfoss | November 2022

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Features and Options
Optional Integrated Reservoir
The BDU-06S and BDU-10S are designed with optional integrated reservoir. The optional Integrated
reservoir is shown in the figure on the right.

14

75.5 ± 1.5

25.5

Ø 71

15

Dimensions ofWidths AcrossFlats of Hexagon
0
30 -0.8

7/8-14UNF

Ø 60

P/N BDU-10S-TANK
P400231

FilterThe BDU-10S is designed with Built-in filter. BDU-21L/H is designed with optional Integrated filter, whichis shown in the figure on the right. The filter connection is designed with consideration given to thescrewed type steel pipe fitting that is an option. An external filter is required in the charge pump inlet line
for BDU- 10L. This filter should not have a bypass and should be changed regularly to ensure system
reliability.
Screwed Type
Steel Pipe Fitting

Ø 84

Ø 59.7

Ø 37

32

3/4-16 UNF screw

P/N H-3101069
69

3/4-16 UNF screw

70.8

P/N 05EL-BD© Danfoss | November 2022

P400232

BC152886484098en-000208 | 25

Technical Information
BDU Series Hydrostatic Transmissions
Features and Options
Fan
The operating temperature of the BDU transmission becomes hot when operated at a heavy load for
long, continuous time. To avoid a reduction in the life of the BDU transmission or risking immediate
failure, a cooling fan may be installed on the input shaft or external reservoir to be effective as heatexchanger may be installed. The BDU transmission is available with optional fan integrated with the belt
drive device for the input shaft. The detailed outlines are shown in the Installation Drawings on page 35.
Optional Fan for Cooling
P/N

Rotation

H-1030826

CW

H-1030827E

CCW
Rot ationWindØ 177.8

CCW

Ø 7.1
31.8
P400233

Optional Fan for Cooling

26 | © Danfoss | November 2022

P/N

Rotation

H-1030826

CW

H-1030827E

CCW

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Component Selection
Selecting the proper transmission for a vehicle begins with determining the maximum system pressureby using tractive effort of the vehicle and the maximum vehicle speed required. The transmission
selected must meet both requirements.
Maximum System Pressure
Maximum operating system pressure should be calculated at maximum tractive effort condition.
Maximum tractive effort condition is assumed at vehicle with maximum weight transfer from pushing or
pulling implements at maximum grade of slope. First, calculate BDU motor torque by using the following
equation:
Equation-1

•
•
•
•
•
•

MTQ_ME = Output torque of BDU motor at maximum tractive effort condition in Nm
PR_ME = Pull Ratio at maximum tractive effort (See below)
VW_ML = Gross vehicle weight with maximum loaded weight in kgf
LR = Tire Radius in meters
FDR = Transaxle Final Drive Ratio
EFF_FD = Transaxle Final Drive Efficiency

The hydrostatic transmissions in many applications are used in conjunction with readily available
transaxles. In order to meet both requirements of high output torque at operating mode and high speed
at traveling mode, the transaxles with two kinds of shifts, Hi and Lo are used in some applications. In suchtransaxles, use Lo shift ratio as FDR in equation-1 and -4 to calculate maximum system pressure.
A useful parameter for determining tractive effort is "Pull Ratio". Pull Ratio is a dimensionless term that is
the ratio of tractive effort to gross vehicle weight. It is generally constant for each class of vehicle. These
values may be used when actual vehicle tractive efforts are not known. In a typical agriculture applicationfor BDU application, Pull Ratio for the highest load mode can be calculated from the primary componentsof pull ratio: rolling resistance, grade motion resistance by a function of slope, machine function motion
resistance and drive configuration motion resistance. In such cases, pull ratio is determined by using thefollowing equation:
Equation-2

•
•
•
•

RR = Rolling resistance. See SD Application manual
GR = Motion resistance of Grade. See SD Application manual
MF = Machine function motion resistance, See SD Application manual
DC = Drive configuration motion resistance, See SD Application manual

Then, maximum system pressure can be calculated by using MTQ_ME and the following quation:
Equation-3© Danfoss | November 2022

BC152886484098en-000208 | 27

Technical Information
BDU Series Hydrostatic Transmissions
Component Selection•••

SPR_ME = Maximum BDU system pressure operated at Maximum tractive effort mode in bar
DP = Motor Displacement of selected BDU transmissions in cm3
MEF_MO = Motor Mechanical Efficiency of BDU transmission in this mode

Select appropriate BDU size which will give SPR_ME, not to exceed the value of maximum systempressure allowed in the technical specification, because BDU is generally applied without systempressure relief valves.
If appropriate BDU size satisfies maximum system pressure, determine the BDU output speed at
maximum tractive effort mode by using the following equation:
Equation-4••

MSP_ME = The BDU output speed at maximum tractive effort condition in min-1 (rpm)
VSP_ME = The vehicle speed requested for maximum tractive effort mode in m/s

Confirm the BDU output speed calculated to satisfy the maximum output speed (intermittent) in thetechnical specification.
Input Power
Calculate required input power of BDU by using the following equation:
Equation-5••

PW_ME = BDU Input power required for maximum tractive effort mode in kW
OEF_BDU = BDU unit overall efficiency for this mode

If PW_ME is larger than Input power (Maximum) of selected BDU, VSP_ME should be limited to satisfy
maximum BDU input power. If the calculated speed exceeds the technical specification, the transaxle
final drive ratio or tire size may need to be changed.
Maximum vehicle speed is generally recommended in traveling mode. Calculate maximum BDU speed byusing the following equation:
Equation-6••

MSP_TR = The BDU output speed for traveling mode in min-1 (rpm)
VSP_TR = The vehicle speed requested for traveling mode in m/s

Use Hi shift ratio as FDR in Equation-6 if the Transaxle Final Drive has two shifts.
Confirm MSP_TR to satisfy the maximum output speed (intermittent) in the technical specification. If
MSP_TR is not satisfied, FDR (Hi shift) may need to be changed. It is also necessary to determine thesystem pressure for traveling mode (SPR_TR) to satisfy maximum system pressure (intermittent) allowedin the technical specification. SPR_TR is calculated by using equation -1, -2 and -3 with parameters oftraveling mode.
28 | © Danfoss | November 2022

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Component Selection
Calculate the required BDU input shaft speed to satisfy maximum BDU output shaft speed by using thefollowing equation:
Equation-7••

PSP_RIN = required BDU input shaft speed in min-1 (rpm)
VEF_BDU = BDU volumetric efficiency for this mode

Confirm BDU input shaft speed is larger than PSP_RIN.
Unit LifeThe unit life of selected BDU transmissions should be determined by using average system pressure
under overall operating modes, because vehicles generally operate in their maximum tractive effort
mode for a small percentage of their life. If a duty cycle for a transmission is known, weighted averagesystem pressure can be calculated and can estimate the life expectancy of the transmission selected. The
duty cycle can be assumed for instances including several modes. Calculate weighted average systempressure by using the following equation:
Equation-8

•
•
•
•

SPR_AV = weighted average system pressure. This is the mean pressure of the duty cycle in bar
SPR_ME = the system pressure for maximum tractive effort mode and T_ME is its time in the duty
cycle
SPR_NE = the system pressure at the normal tractive effort which means with normal weight and at
0% Grade and T_NE is its time in the duty cycle
SPR_TR = the system pressure for traveling mode and T_TR is its time in the duty cycle

If needed, define other system pressures at other operating conditions and add them to the equation.
The BDU Unit Life hours at weighted average pressure is determined by using the following equation:
Equation-9•••

LH = Unit Life hours of selected BDU at the duty cycle estimated
SPR_RH = The system pressure at Rated Unit Life (See table A)
PSP_IN = The input shaft speed of BDU unit. Normally, input shaft speed of BDU is constantConfirm LH of selected BDU to satisfy the Life requirement. If LH is shorter than the requested
specification, the next larger size transmission may be needed and the repeat the calculation for
Component Selection on other BDU using Equation -1 through -9. Contact Danfoss for assistance incorrect transmission selection.

© Danfoss | November 2022

BC152886484098en-000208 | 29

Technical Information
BDU Series Hydrostatic Transmissions
Component Selection
Table A
Frame
Parameter

Unit

RH

hour

BDU-06S BDU-10S BDU-10L

30 | © Danfoss | November 2022

300

300

1000

BDU-21L BDU-21H
1600

2500

SPR_RH

bar

55

70

70

70

70

BSP_OP

min-1

3000

3000

3000

3000

3000

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Model CodeBDU : Model Code (A - B - C - D - E)
A

B

C

D

E

F

G

H

J

K

BDU -

A - Displacement
Code

Description

06

6 cm3

10

10 cm321

21 cm3

06S

10S

10L

21L

21H

06S

10S

10L

21L

21H

06S

10S

10L

21L

21H

06S

10S

10L

21L

21H

06S

10S

10L

21L

21H

B - Design
Code

Description

S

Standard

LLong Life

H

High Pressure

C - Rotation
Code

Description

W

Bi-directional rotation

R

Clockwise rotation

L

Counter-Clockwise rotation

D - Contrl Arm Location
Code

Description

R

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

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

E - Output Shaft© Danfoss | November 2022

Code

Description

J13

JIS Spline 15×13×1.0

J14

JIS Spline 20×14×1.25

J18

JIS Spline 20×18×1.0

K18

JIS Spline 15×18×0.75

S16

SAE Spline 32/64 - 16T

S22

SAE Spline 32/64 - 22T

BC152886484098en-000208 | 31

Technical Information
BDU Series Hydrostatic Transmissions
Model CodeBDU : Model Code (F - G)
A

B

C

D

E

F

G

H

J

K

BDU -

F - Check & Relief Valve (Left-hand side viewing from Housing)
Code

Description

BB

Ball Check Valve00

Poppet-type Check Valve07

Check Valve w/dia = 0.7 orifice

08

Check Valve w/dia = 0.8 orifice10

Check Valve w/dia = 1.0 orifice12

Check Valve w/dia = 1.2 orifice

R0

Check and High Pressure Relief Valve 210 bar

R1

Check and High Pressure Relief Valve 175 bar

R2Check and High Pressure Relief Valve 140 bar

RA

Check and High Pressure Relief Valve 210 bar w/dia=0.7 twin orificeRB

Check and High Pressure Relief Valve 210 bar w/dia=0.85 orifice

06S

10S

10L

21L

21H

06S

10S

10L

21L

21H

G - Check & Relief Valve (Right-hand side viewing from Housing)32 | © Danfoss | November 2022

Code

Description

BB

Ball Check Valve00

Poppet-type Check Valve07

Check Valve w/dia = 0.7 orifice

08

Check Valve w/dia = 0.8 orifice10

Check Valve w/dia = 1.0 orifice12

Check Valve w/dia = 1.2 orifice

R0

Check and High Pressure Relief Valve 210 bar

R1

Check and High Pressure Relief Valve 175 bar

R2Check and High Pressure Relief Valve 140 bar

RA

Check and High Pressure Relief Valve 210 bar w/dia=0.7 twin orificeRB

Check and High Pressure Relief Valve 210 bar w/dia=0.85 orificeBC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Model CodeBDU : Model Code (H - J - K)
A

B

C

D

E

F

G

H

J

K

BDU -

H - Input shaft / PTO shaft Configuration & Charge Pump Displacement
Code

Description

KAO

Straight-keyed D=15mm shaft / None & w/o Charge Pump

KBO

Straight-keyed D=15mm shaft / None & w/o Charge Pump

KB1

Straight-keyed D=15mm shaft / None & w/1.9cm3 Charge Pump

KC1

Straight-keyed D=17mm shaft / None & w/2.1cm3 Charge Pump

KC2

Straight-keyed D=17mm shaft / None & w/3.1cm3 Charge Pump

PB1

Straight-keyed D=15mm shaft /Straight 12.7 mm shaft & w/o Charge
Pump

PB2

Straight-keyed D=15mm shaft /JIS Serration 12 x 23 x 0.5 shaft & w/oCharge Pump

PB3

Straigt-keyed D=15mm shaft /Straight 12.6 mm shaft & w/2.4cm3
Charge Pump

PB4

Straight-keyed D=15mm shaft /JIS Serration 12 x 23 x 0.5 shaft & w/
2.4cm3 Charge Pump

PC1

Straight-keyed D=17mm shaft /JIS Spline 15 x 13 x 1.0 shaft & w/2.1cm3
Charge Pump

PC2

Straight-keyed D=17mm shaft /JIS Spline 15 x 13 x 1.0 shaft & w/3.1cm3
Charge Pump

PC5

Straight-Keyed D=17mm shaft /SAE Spline 32/64 -16T & w/2.1cm3
Charge Pump

PC6

Straight-Keyed D=17mm shaft /SAE Spline 32/64 -16T & w/3.1cm3
Charge Pump

06S

10S

10L

21L

21H

06S

10S

10L

21L

21H

06S

10S

10L

21L

21H

J - Bypass & Nuetral Valve
Code

Description

N

None

A

w/Nuetral Valve Pressure 35 bar w/dia=1.0 orificeB

w/Bypass Valve

K - Special Hardware© Danfoss | November 2022

Code

Description

NNN

None

WOL

Oil-filled in case

BC152886484098en-000208 | 33

Technical Information
BDU Series Hydrostatic Transmissions
Recommended Installation and Maintenance
Housing Installation
The center section of BDU transmission has 4 holes for fixing screws. The screws should be inserted in theholes and tightened to specifications. *Fitting Torque 1569 ~ 2058 N·cm
Shaft Installation
The input shaft of the BDU transmission should be connected to the prime mover by a belt drive device,sheave or coupling. When using a belt drive device, the radial load on the input shaft should not exceed
the maximum allowable load shown in Shaft Load on page 18.
When installing the BDU motor shaft to the gearbox or to other devices directly, utilize the groove on thecenter section of the BDU transmission, which is located concentric to the motor shaft, to ensure theaccuracy of concentricity. When using the coupling for connection of the shaft, ensure the accuracy ofconcentricity is kept in the region of ±0.025mm. Do not beat the coupling strongly into the shaft with ahammer. It is recommended the shaft to be lubricated when using a spline shaft.
Start Up Procedure
After installing the BDU transmission and corresponding pipeline connection, remove the case drain port
plug from the housing. Fill the BDU transmission case with the recommended oil through the drain port.
BDU-10S is filled with oil at the plant shipment.
Make sure the control shaft of the BDU transmission is set to the neutral position. The BDU transmission
pump must be at zero position. Depress the bypass valve plunger manually to connect both side of themain hydraulic circuit to housing case. Allow the prime mover to turn at idling speed. Turn the control
shaft and oil fills into main circuits. Stop depressing the bypass valve plunger. Then, the output shaft will
start to turn. Check the oil tank or reservoir level and refill the oil to the proper level if necessary. Repeat
the control shaft movement from full displacement in one direction to full displacement in the opposite
direction. Oil should not contain air trapped in the oil during the initial operation.
Operation
Check all joints and connections for leaks, and check that the oil tank or reservoir level is proper at thetime of first operation and every day. Start the prime mover turning in the neutral position of the control
shaft of the BDU transmission.
MaintenanceIf some water, dust or grease are mixed in, with the transmission oil, change to new recommended oil.
Always keep at less than 0.1 % water in the transmission oil. It is recommended to change oil and filter
every year or at the every 500 operating hours.
Packing and Transportation

C Caution
When shipping or transporting the BDU, be sure to packthe unit so that the input shaft faces downward as shownright to avoid internal parts fall out. This is also
recommended for long-term storage.

P400784

34 | © Danfoss | November 2022

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Installation Drawings

BDU-06S : Ports and Dimensions
+0.03
5 0

+2
144 -1+1
114 -0.15(30)

Rese rvoir Fitting

68 ± 0.5
51 ± 0.4

22

A
A

4.1

2.4

3.5
Ø 35

Ø 65
+0.03
Ø 47 0B

3A

C

26.5 ± 0.5

Section A-Ab

56 ± 0.5

a

+0.5
+0.5
15° -2.5 15° -2.5

0
Ø 15 0.036

14 ± 0.2

7/8-14UNF-2B
SAEStraight THD.
O Ring Boss

11.9 ± 0.1

Rese rvoir Fitting
7/8-14UNF-2B
SAEStraight THD.
O Ring Boss
(Both Sides)

15
Bypass Valve

27 ± 0.5

19+0.8
56 -0.5+0.8
91 -0.555 ± 0.555 ± 0.5

65.5 ± 0.4

65.5 ± 0.4

52+1
97 -0.1560 ± 0.548

48

45 ± 0.18
25.5
R7.5

Bypass Valve
Open

Ø6

2.9

45 ± 0.18

51 ± 0.8

62.4 ± 0.7
Bypass Valve Close

65 ± 0.05

20

R7.5

45 ± 0.18

45 ± 0.18
52

View C+0.2
4- Ø 8.7 0
Ø 71

P400234.
© Danfoss | November 2022

BC152886484098en-000208 | 35

Technical Information
BDU Series Hydrostatic Transmissions
Installation Drawings
Option CodeR

L

Input Rotation as Seen From A Direction

CW

CCW

Control Shaft Rotation
Output Rotation as Seen From B Direction

a

b

a

b

CCW

CW

CW

CCW

The tightening torque to install HST is 1569 to 2058 N·cm.

BDU-06S : Control Arm Location
81

13.5

81

+0.8
0
7.5

13.5

+0.8
0

7.5

B

B

+0.12
Ø5 0
THR

+0.12
Ø5 0
THR

-0.006
12 -0.024

10 ± 0.2

View B-B
Left-hand side viewing from input shaft(when pump located upside)
Option Code : L

Right-hand side viewing from input shaft(when pump located upside)
Option Code : R

P400235

4 ± 0.5

0Ø 14.8 -0.15

05 -2.5030 -2.5

0
20 -2.5

17

Ø 15

0
30 -2.5

Ø 15

0
Ø 13.495 -0.15

BDU-06S : Motor Shaft

Involute Spline
Fillet Root Side Fit
SAE 1963 class 1
Pitch Diameter = 12.7
Pressure Angle = 30 °Number of Teeth = 16
Spline Pitch = 32/64

Involute Spline
JIS 15x13x1.0 class a
Tooth Profile Short Teeth
Module = 1.0
Pressure Angle = 20 °Number of Teeth = 13
Pitch Diameter = Ø13.0
Addendum Modification Coefficient = 0.8

36 | © Danfoss | November 2022

P400236

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Installation Drawings
BDU-10S/10L : Ports and Dimensions+1
121 -0.15
67 ± 0.5

Reservoir Fitting

61.5 ± 0.4+0.5
21° -2.5

BDU-10L
Charge Pump
Suction Port

a

21°

+0.5
-2.5

30

b

7/8- 14UNF-2B
SAE Straight THD.
O Ring Boss

25 ± 0.566.75 ± 0.5

15°

A

20

20

B

Reservoir Fitting
Reservoir Fitting
7/8- 14UNF-2B
SAE Straight THD.
O Ring Boss
(Both Sides)

3.5

7/8- 14UNF-2B
SAE Straight THD.
O Ring Boss

49 ± 0.5

6+0.03
Ø 47 0C

14 ± 0.2
25 ± 0.5
27 ± 0.5

Bypass Valve

18 ± 0.3
68.5 ± 0.5

103

54.5

68.5 ± 0.5
54.5

53 ± 0.18

53 ± 0.18

75 ± 0.05
65 ± 0.8

04- Ø 9 -0.3 THR
2.9

77.4 ± 0.7

Bypass Valve Close

Charge Pump
Suction Port
7/8- 14UNF-2B
SAE Straight THD.
O Ring Boss

Bypass ValveOpen

BDU-10L

63

66.5 ± 0.5+0.8
97 -0.553 ± 0.18

Ø653 ± 0.18

View C

Mounting HolesØ 75
P400237.

© Danfoss | November 2022

BC152886484098en-000208 | 37

Technical Information
BDU Series Hydrostatic Transmissions
Installation Drawings
Option CodeR

L

Input Rotation as Seen From A Direction

CW

CCW

Control Shaft Rotation

a

b

a

b

Output Rotation as Seen From B Direction

CW

CCW

CCW

CW

The tightening torque to install HST is 1569 to 2058 N·cm.

BDU-10S/10L : Control Arm Location
84

13.5

84

13.5

+0.8
0
7.5

+0.8
0

7.5

E

E

-0.006
Ø12 -0.024

E-0.006
Ø12 -0.024

E

+0.12
5 0

+0.12
5 0

10 ± 0.15

View E-E
Left-hand side viewing from input shaft(when pump located upside)
Option Code : L

38 | © Danfoss | November 2022

Right-hand side viewing from input shaft(when pump located upside)
Option Code : R

P400238

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Installation Drawings

Ø14.8 0-0.15

030 -2.50
2.5-2.5

0
24 -2.50
2.5-2.5
4 ± 0.5

Ø15

17

Ø15

Ø14.8 0-0.15

BDU-10S/10L : Motor Shaft

Involute Spline

Involute Spline
JIS 15x13x1.0 class a
Tooth Profile = Short Teeth
Module = 1.0
Pressure Angle = 20°
Number of Teeth = 13
Pitch Diameter = Ø13.0
Addendum Modification Coefficient = 0.8

030 -2.5
4

JIS 15x18x0.75 class a
Tooth Profile = Short Teeth
Module = 0.75
Pressure Angle = 20°
Number of Teeth = 18
Pitch Diameter = Ø13.5
Addendum Modification Coefficient = 0.5

Shaft : JIS 15x18x0.75
Option Code : K18

0
5 -2.5

Ø15

Ø13.495 0-0.15

Shaft : JIS 15x13x1.0
Option Code : J13

Involute Spline
Fillet Root Side Fit
SAE 1963 class 1
Pitch Diameter = 12.7
Pressure Angle = 30°
Number of Teeth = Ø16
Spline Pitch = 32/64© Danfoss | November 2022

Shaft : SAE 32/64-16T
Option Code : S16

P400239

BC152886484098en-000208 | 39

Technical Information
BDU Series Hydrostatic Transmissions
Installation Drawings
BDU-10S : Shaft Configuration+2
165 -18
F

0
Ø12.7 -0.011

30

0Ø15 -0.036

+1
24 -2

3

30

18
G

G

F

Pump Shaft : 15mm Straight KeyedPTO Shaft : None
Charge Pump : None
Option Code : KB

8F0
Ø15 -0.036+2165 -1F

Pump Shaft : 15mm Straight KeyedPTO Shaft : 12.7mm Straight Keyed
Charge Pump : None
Option Code : PB1

+0.03
5 0

+2
165 -1

+1
30 -2

+0.5
22 0
11.9 ± 0.1

FF
Model Involute Serration
Module = 0.5
Pressure Angle = 45°
Number of Teeth = 23
Pitch Diameter = Ø11.5

9.6 ± 0.1
Pump Shaft : 15mm Straight KeyedPTO Shaft : Serration 12x23x0.5
Charge Pump : None
Option Code : PB2

40 | © Danfoss | November 2022

Section F-F

+0.03
5 0

8

30

0
Ø15 -0.036

0Ø12 -0.05(Effective Length of Spline)

Section G-G
P400241

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Installation Drawings
BDU-10L : Shaft Configuration and Charge Pumps Displacement
33

33

+2
165 -116

8

0
Ø15 -0.036

30
H

2-R7

8

0
Ø15 -0.036

10

H

Ø41
Pump Shaft : 15mm Straight KeyedPTO Shaft : None
Charge Pump : 1.9 cc/rev
Option Code : KB1
+1
55 -2

33

33

+0.5
22 0

25
1.7

(Effective Length of Spline)

J

30
H

0
Ø12 -0.05

Ø42

Module = 0.5
Pressure Angle = 45°
Number of Teeth = 23
Pitch Diameter = Ø11.5
2-R7
-0.02
Ø35 -0.05

1.4

1.65

Model Involute Serration+2
165 -1

H

R1

+0.23
2.7 0

Ø58

2-R0.5

Pump Shaft : 15mm Straight KeyedPTO Shaft : Serration 12x23x0.5
Charge Pump : 2.4 cc/rev
Option Code : PB4(Ø35)

2-R0.233+1
50.1 -233+2
165 -1

Ø31.8 ± 0.05

Ø56

View J

18

17MAX.

1.65

14 MAX.

Ø42-0.02
Ø35 -0.05

0Ø12.6 -0.018

J
2-R7

8

30
H
I
I

0
Ø15 -0.036

25
3

H

R1

+0.03
5 0

Pump Shaft : 15mm Straight KeyedPTO Shaft : 12.7mm Straight Keyed
Charge Pump : 2.4 cc/rev
Option Code : PB3

+0.03
5 0

Ø58

9.6 ± 0.1

Section I-I

11.9 ± 0.1

Section H-H

P400240© Danfoss | November 2022

BC152886484098en-000208 | 41

Technical Information
BDU Series Hydrostatic Transmissions
Installation Drawings
BDU-21L/21H : Ports and Dimensions
150 ± 1.0
Charge Pump
Suction Port

77.5
66

9/16- 18UNF-2B
SAE Straight THD.
O Ring BossIn case ofExternal Filter

40’+0° 10’°22° -2aCharge Pump
Suction Port

Charge Pump Suction Port30

In case of External Filter

22° +0° 40’-2° 10’55 ± 0.5

3/4- 16UNF-2B
SAE Straight THD.
O Ring BossIn case ofExternal Filter

55 ± 0.5bDrain Port

Charge Pump
Suction PortA

85 ± 0.07
80.5

CPlug for C & HPRV
Only for BDU-21H(Both Side)

Bypass Valve Close

3.5

+0.03
Ø 47 0

4.5

9/16- 18UNF-2B
SAE Straight THD.
O Ring Boss
W/Option Filter(Both Side)

B

73
60

3/4- 16UNF-2B
SAE Straight THD.
O Ring Boss
(Both Side)16

60 ± 0.7
122 ± 1.0

3/4- 16UNF-2B
SAE Straight THD.
O Ring Boss

Bypass Valve78

78

53 ± 0.18

53 ± 0.18

134 ± 1.5

4
Bypass ValveOpen

Drain PortØ 90
4- Ø 8.5 THR
Mounting Holes

53 ± 0.18

53 ± 0.18

61

61

View C
P400243

42 | © Danfoss | November 2022

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Installation Drawings
Option CodeR

L

Input Rotation as Seen From A Direction

CW

CCW

Control Shaft Rotation
Output Rotation as Seen From B Direction

a

b

a

b

CCW

CW

CW

CCW

The tightening torque to install HST is 1569 to 2058 N·cm.

BDU-21L/21H : Control Arm Location
97

97

+0.8
15 0

+0.8
15 0

9

9

-0.006
Ø15 -0.030

EE-0.006
Ø15 -0.030

E

+0.12
Ø6 0

E

+0.12
Ø6 0

12 ± 0.2

View E-E
Left-hand side viewing from input shaft(when pump located upside)
Option Code : L© Danfoss | November 2022

Right-hand side viewing from input shaft(when pump located upside)
Option Code : R

P400242

BC152886484098en-000208 | 43

Technical Information
BDU Series Hydrostatic Transmissions
Installation Drawings
BDU-21L/21H : Motor Shaft

0
21.5 -0.5

37

32
16 2

Model Involute Spline
20x18x1.0 class a
Tooth Profile = Short Teeth
Module = 1.0
Pressure Angle = 20°
Number of Teeth = 18
Pitch Diameter = Ø18.0
Addendum Modification Coefficient = 0.8

Shaft : JIS 20x18x1.0
Option Code : J18

32
5
4

Ø20

Ø18.2630-0.15

Model Involute Spline
20x14x1.25 class a
Tooth Profile = Short Teeth
Shaft : JIS 20x14x1.25
Module = 1.25
Option Code : J14
Pressure Angle = 20°
Number of Teeth = 14
Pitch Diameter = Ø17.5
Addendum Modification Coefficient = 0.8

Ø19.8

0
-0.1
Ø20

Ø19.75

Ø20

0
-0.15

(Effective Length of Spline)

Model Involute Spline
Fillet Root Side Fit
SAE 1963 class 1
Pressure Angle = 30°
Number of Teeth = 22
Pitch Diameter = Ø17.643
Spline Pitch = 32/64

44 | © Danfoss | November 2022

Shaft : SAE 32/64-22T
Option Code : S22

P400244

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Installation Drawings
BDU-21L/21H : Shaft Configuration and Charge Pump Displacement
40

18

40

195 ± 2.0
12

3

36
60 °

Ø40

0
Ø17 -0.036

R7

F

F

Ø72

Pump Shaft : 17mm Straight Keyed (Key Length 36mm)
PTO Shaft : None
Charge Pump : 3.1cc/rev (for 21H)
Option Code : KC2
40

16

40

195 ± 2.0
10

3

36
R7

Ø40

0
Ø17 -0.036

F

F

Ø72

Pump Shaft : 17mm Straight Keyed (Key Length 36mm)
PTO Shaft : None
Charge Pump : 2.1cc/rev (for 21L)
Option Code : KC1
4040

65 ± 2.0
25 ± 0.2518185 ± 2.00
35 -0.5+0.5
18 0 15

3

26

G

F

F
Ø74

0
Ø17 -0.036

Ø15

R10

0
Ø14.8 -0.1

7

+0.25
4.7 0

Section F-F

Pump Shaft : 17mm Straight Keyed (Key Length 26mm)
PTO Shaft : Involute Spline JIS 15x13x1.0
Charge Pump : 2.1cc/rev (for 21L), 3.1 cc/rev (for 21H)
Option Code : PC1 (2.1cc/rev), PC2(3.1 cc/rev)

Ø36

13.9 ± 0.1

JIS 15x13x1.0 Class a
Tooth Profile = Short Teeth
Module = 1.0
Pressure Angle = 20°
Number of Teeth = 13
Pitch Diameter = Ø13.0
Addendum Modification
Coefficient = 0.8

0Ø42 -0.039

+0.03
5 0

Model Involute Spline

View G-G
P400245© Danfoss | November 2022

BC152886484098en-000208 | 45

Technical Information
BDU Series Hydrostatic Transmissions
Installation Drawings40

189 ± 2.0

65 ± 2.040035 -0.525 ± 0.25

+0.5
18 0

18

15

3

30

G

F

F

Model Involute Spline
JIS 15x13x1.0 Class a
Tooth Profile = Short Teeth
Module = 1.0
Pressure Angle = 20°
Number of Teeth = 13
Pitch Diameter = Ø13.0
Addendum Modification
Coefficient = 0.8

Section F-F40

185 ± 2.0

62± 2.040
2215View G-G0
35 -0.5
+0.5
18 0

Ø36

13.9 ± 0.1

+0.25
4.7 0
Pump Shaft : 17mm Straight Keyed (Key Length 30mm)
PTO Shaft : Involute Spline JIS 15x13x1.0
Charge Pump : 2.1cc/rev (for 21L), 3.1 cc/rev (for 21H)
Option Code : PC3 (2.1 cc/rev), PC4(3.1 cc/rev)0Ø42 -0.039

+0.03
5 0

Ø74

0
Ø17 -0.036

Ø15

R10

0
Ø14.8 -0.1

7

15

0
Ø13.495 -0.15

7
3

26
F

F

Model Involute Spline
Ø74

46 | © Danfoss | November 2022

Fillet Root Side Fit
SAE 1963 Class 1
Module = 1.0
Pressure Angle = 30°
Number of Teeth = 16
Pitch Diameter = Ø12.7
Spline Pitch = 32/64

Pump Shaft : 17mm Straight Keyed (Key Length 26mm)
PTO Shaft : Involute Spline SAE 32/64-16T
Charge Pump : 2.1cc/rev (for 21L), 3.1 cc/rev (for 21H)
Option Code : PC5 (2.1 cc/rev), PC6(3.1 cc/rev)0Ø17 -0.036

Ø15

R10

G

P400247

BC152886484098en-000208

Technical Information
BDU Series Hydrostatic Transmissions
Installation Drawings
Optional Fan
Rot ationWindØ177.80
Ø84 -1.5(4 Places) Ø7.1

L

Ø88.9

CCW

23
2.5
18.5

A

+0.4
Ø24 -0.6

Ø45.7

31.8
P400248© Danfoss | November 2022

BC152886484098en-000208 | 47

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© Danfoss | November 2022

BC152886484098en-000208