Technical Information

Orbital Motors
Generalwww.danfoss.com

Technical Information
General, Orbital Motors

Revision history

Table of revisions
Date

ChangedRev

December 2021

Comprehensive catalogue update

0401

Changed document number from 'BC00000083' and '520L0232' to 'BC152886483554'

0301

July 2018

updated to Engineering Tomorrow design

0203

June 2015

Minimum speed updated

0202

May 2015

Motor version removed from section 'Motors woth integrated flushing valve

CB

November 2014

Converted to Danfoss layout - DITA CMSCAJune 2005

2 | © Danfoss | December 2021

BA

BC152886483554en-000401

Technical Information
General, Orbital Motors
Contents
A wide range of Orbital Motors
Orbital Motors Introduction......................................................................................................................................................... 5
Orbital Motors Features............................................................................................................................................................ 5
Technical Features...................................................................................................................................................................... 5
Orbital Motors Application Areas..........................................................................................................................................5
Orbital Motors Literature Overview...........................................................................................................................................6
Conversion Factors
Orbital Motors, General
Operating Principle..........................................................................................................................................................................8
Gearwheel set...............................................................................................................................................................................8
Distributor valve.......................................................................................................................................................................... 8
Disc valve with valve drive................................................................................................................................................. 8
Selection of Motor Type
Features of main types................................................................................................................................................................... 9
OMT, OMV......................................................................................................................................................................................9
TMT...................................................................................................................................................................................................9
Motor Variants................................................................................................................................................................................... 9
Wheel motor................................................................................................................................................................................. 9
Short motors...............................................................................................................................................................................10
Ultrashort motor....................................................................................................................................................................... 10
Motors with integrated negative holding brake...........................................................................................................10
Motors with integrated flushing valve..............................................................................................................................11
Motors with tacho connection............................................................................................................................................ 11
Motors with speed sensor..................................................................................................................................................... 12
Selection of Motor Size
Build-up of the Function Diagram........................................................................................................................................... 13
Continuous operation/intermittent operation/peak load.........................................................................................13
Efficiency......................................................................................................................................................................................14
Volumetric efficiency...............................................................................................................................................................14
Example........................................................................................................................................................................................14
Hydraulic mechanical efficiency..........................................................................................................................................15
Example:.......................................................................................................................................................................................15
Total efficiency...........................................................................................................................................................................16
Minimum speed..............................................................................................................................................................................16
Bearing Dimensioning
Shaft load and bearing life time............................................................................................................................................... 17
Relationship between Bearing Life Time and Speed........................................................................................................ 17
Relationship between Shaft Load and Bearing Life Time................................................................................................17
Relationship between permissible shaft load and speed............................................................................................... 18
Maximum Radial Shaft Load...................................................................................................................................................... 18
Hydraulic Systems
Max. Pressure on the Shaft Seal................................................................................................................................................ 19
Standard shaft seal (NBR).......................................................................................................................................................19
High-pressure shaft seal (NBR).............................................................................................................................................19
Viton shaft seal (FPM)..............................................................................................................................................................19
Characteristics of sealing materials....................................................................................................................................19
Short/ultra-short motors........................................................................................................................................................20
Drain Line..........................................................................................................................................................................................20
Application..................................................................................................................................................................................20
Oil flow in the drain line......................................................................................................................................................... 20
Braking............................................................................................................................................................................................... 20
Braking torque........................................................................................................................................................................... 21
Opening pressure for the dual shock valve.....................................................................................................................21
Replenishment...........................................................................................................................................................................21
Seeping.........................................................................................................................................................................................23
Brake Motors....................................................................................................................................................................................23© Danfoss | December 2021

BC152886483554en-000401 | 3

Technical Information
General, Orbital Motors
Contents
OMT FX, OMT FL and TMT FL................................................................................................................................................24
OMT FH.........................................................................................................................................................................................24
Installation, Starting Up, Maintenance and Oil Types.......................................................................................................25
Design in brief............................................................................................................................................................................25
Combination in brief............................................................................................................................................................... 25
Starting up and running in the hydraulic system......................................................................................................... 25
Signs of air in the hydraulic system....................................................................................................................................26
If there is air in the system.....................................................................................................................................................26
During operation...................................................................................................................................................................... 26
Maintenance...............................................................................................................................................................................26
Oil Types.......................................................................................................................................................................................26
Mineral oils.............................................................................................................................................................................26
Non-flammable or biodegradable fluids.................................................................................................................... 26
Temperature, Viscosity and Filtering...................................................................................................................................... 27
Temperature...............................................................................................................................................................................27
Viscosity........................................................................................................................................................................................27
Filtering........................................................................................................................................................................................ 28

4 | © Danfoss | December 2021

BC152886483554en-000401

Technical Information
General, Orbital Motors
A wide range of Orbital Motors
Orbital Motors Introduction
Danfoss is a world leader within production of low speed orbital motors with high torque. We can offer
more than 1500 different orbital motors, categorized in types, variants and sizes (including different shaft
versions).
The motors size vary (rated displacement) from 130 to 800 cm3 [7.9 to 48.9 in3] per revolution.
• Motor sizes:‒ OMT and OMV

‒
‒
‒
‒

TMK
TMT
TMTHW
TMVW

Speeds range up to approximate 600 min-1 (rpm).
Maximum operating torques up to 3400 N•m [30090 lb•in] (peak) and maximum outputs up to 70 kW [95hp].
Orbital Motors Features

•
•
•
•
•
•
•
•
•
•

Smooth running over the entire speed range
Constant operating torque over a wide speed range
High starting torqueHigh return pressure without the use of drain line (high pressure shaft seal)
High efficiency
High radial and axial bearing capacity
Long life under extreme operating conditions
Robust and compact design
For applications in both open and closed loop hydraulic systems
Suitable for a wide variety of hydraulics fluids

Technical Features
The program is characterized by technical features appealing to a large number of applications and by
motors that can be adapted to a given application.
Adaptions comprise the following variants:
Motors with:‒ integrated negative holding brake•‒ speed sensor‒ black finish paint••

Short motors without bearings or Ultra short motors
Wheel motors with recessed mounting flange

Orbital Motors Application Areas
The orbital motors are used in the following application areas:
Construction equipment

•
•
•
•
•
© Danfoss | December 2021

Agricultural equipment
Material handling & Lifting equipment
Forestry equipment
Lawn and turf equipment
BC152886483554en-000401 | 5

Technical Information
General, Orbital Motors
A wide range of Orbital Motors•••

Machine tools and stationary equipment
Marine equipment
Special purpose

Orbital Motors Literature Overview
A general catalog of all Orbital Motors with technical data gives a quick motor reference based on:
selection of orbital motor, function in hydraulic systems, power, torque, speed and capabilities. Moredetailed information can be found in an individual motor catalogs.
Literature title

6 | © Danfoss | December 2021

Literature type

Reference number

Orbital Motors in General

Technical Information

BC152886483554

OMT and OMV Orbital Motors

Technical Information

BC152886483862

TMK, TMKW, TMK FL Orbital Motors

Technical Information

BC152886483785

TMT, TMTU, TMTW, TMT FL Orbital Motors

Technical Information

BC152886483631

TMTHW Orbital Motors

Technical Information

BC152986483537

BC152886483554en-000401

Technical Information
General, Orbital Motors
Conversion Factors
1 Nm = [8.851 lbf.in]
1 cm3 = [0.061 in3]
1 N = [0.2248 lbf ]1 l = [0.22 UK gal]
1 bar = [14.50 psi]
1 l = [0.264 US gal]
1 mm = [0.0394 in]°F = [1.8 °C + 32]© Danfoss | December 2021

BC152886483554en-000401 | 7

Technical Information
General, Orbital Motors
Orbital Motors, General
Operating Principle
Orbital motors convert hydraulic energy (pressure, oil flow) into mechanical energy (torque and speed).
Danfoss orbital motors are of fixed displacement high-torque design. For a given oil flow and given
pressure the displacement (size of motor) determines the speed and torque. For a given displacement(size of motor) the speed is determined by the oil flow rate and the torque is determined by the pressure
differential.
Gearwheel set
The operating principle of the motors is based on an internal gear design, consisting of a fixed externalgear reaching against an internal gear through which the output torque and speed are transmitted.
Distributor valve
The distributor valve is driven synchronously by the internal gear through a cardan shaft ensuring thatthe individual chambers of the motor are filled and emptied precisely - without losses.

Disc valve with valve drive
OMT, OMV and TMT motors have a disc valve: The distributor valve has been separated from the output
shaft and it is driven by a short cardan shaft [valve drive]. A balance plate counterbal-ances the hydraulicforces around the distributor valve.

F
E
C

D

B
A
151-1053.10

A: Output shaft D: Valve drive
B: Cardan shaft E: Check valve
C: Gearwheel set F: Disc valve

8 | © Danfoss | December 2021

BC152886483554en-000401

Technical Information
General, Orbital Motors
Selection of Motor Type

151-1374.10

OMT, OMV•••

Gear rim with rollers
Disc valve with separate valve drive
Output shaft supported in tapered roller bearings

TMT

•
•
•

Gear rim with rollers
Disc valve with separate valve drive
Output shaft supported in tapered roller bearings

Features of main types
OMT, OMVOMT and OMV are suitable for continuous operation under rough operating conditions: e.g. highpressures, thin oil, or frequent reversals. The tapered roller bearings make the motors suitable forabsorbing static and dynamic radial loads. Besides the separately driven and hydraulically balanced discvalve, hydraulic and mechanical losses are reduced to a minimum. This gives the motors high efficiency even at high pressures, and good starting characteristics.
TMT
The marked for hydraulic motors has developed generally increasing expectations of the motor
performance, and espacially of a higher pressure level. On some applications the present motor program
no longer fulfils the marked demand. The TMT motors comply with these expectations providing thesame good characteristics as the OMT and OMV motors.
If the application requires very smooth running at low speeds the choice of OMT, OMV or TMT is
recommended.
Motor Variants
Wheel motor
OMT and OMV motors are available in wheel motor versions. The recessed mounting flange makes it
possible to fit a wheel hub or a winch drum so that the radial load acts midway between the two motor
bearings. This gives the best utilisation of the bearing capacity and is a very compact solution. Typedesignations of wheel motors are OMTW and OMVW.

151-887.10© Danfoss | December 2021

151-1056.10

BC152886483554en-000401 | 9

Technical Information
General, Orbital Motors
Selection of Motor TypeShort motors
OMT and OMV motors are available in short versions. It can be an advantage to use a short motor forgears that already have the capacity to absorb radial and axial forces.
Type designations are OMTS and OMVS.

151-977.10

Ultrashort motor
OMT, OMV and TMT are available with ultrashort installation dimensions, i.e. without bearings and output
shaft. The ultrashort design allows an opti-mised integration of the motor in the counterpart. Special
installation conditions please contact the Danfoss Sales Organisation.
Type designations: OMTU, OMVU and TMTU.

151-1691.10

Motors with integrated negative holding brake
OMT and TMT with integrated multi-disc brake is available in four versions:OMT FH, OMT FL, OMT FX and TMT FL. The brake is a spring activated multi-disc type that is released by ahydraulic pressure. OMT FH can work with high drop pressure [e.g. piloted from a shuttle valve in open
loop systems], whereas OMT FL, OMT FX and TMT FL release the brake at low pressure [e.g. piloted fromthe charge pump in closed loop systems]. OMT FX are particularly well-suited for applications that requirevery short installation dimensions, - for example in road rollers and wheels.
The design of the OMT F and TMT F motors allows the brake to be used as dynamic emergency brake as
well.

10 | © Danfoss | December 2021

BC152886483554en-000401

Technical Information
General, Orbital Motors
Selection of Motor Type

151-1425.10

Motors with integrated flushing valve
Without any change to their outer dimensions, OMT, OMV and TMT are available with an integrated
flushing valve.
The integrated flushing valve ensures continuous renewal and cooling of the oil in the closed circuit. The
flushing valve is activated by the high pressure side of the motor and allows the flushing flow to pass tothe drain line and the tank.
Type designation: OMT V, OMV V and TMT V .
A

B

151-1627.10

Motors with tacho connection
OMT and OMV motors are available in a version with tacho drive shaft. With a tacho connection the
speed of the motor can be registered.
Type designations are OMT T and OMV T.

151-1372.10© Danfoss | December 2021

BC152886483554en-000401 | 11

Technical Information
General, Orbital Motors
Selection of Motor Type
Motors with speed sensor
OMT and OMV are available with integrated speed sensor. The electric output signal is a standardized
voltage signal that may for example be used with Danfoss' electronic module type EHSC to control the
speed of the motor. The speed is registered by an inductive sensor.
Signal processing and amplification are integrated in the housing of the sensor.
Type designation: OM - EM.

151-1569.10

12 | © Danfoss | December 2021

BC152886483554en-000401

Technical Information
General, Orbital Motors
Selection of Motor Size
When a certain motor type has been selected in accordance with the requirements of the individual
application, the size of the motor is determined according to the torque and speed required for theapplication.
For this purpose use the bar chart on the first pages of the subcatalogues and the function diagram forthe individual motor.
Build-up of the Function Diagram
The function diagram for a hydraulic motor shows the relation between operating torque M (vertical axis)
and speed n (horizontal axis) at different pressure drops ∆p and oil flows Q.
The curves for constant pressure drop and constant oil flow form a network superimposed on thecoordinate system grid. The curves for constant power output N (hyperbolas] and constant total
efficiency ηt are also plotted. The latter curves have a ring form, to as on mussel shells. For this reason
function diagrams are often called shell diagrams.
OMT 160 function diagram

Continuous operation/intermittent operation/peak load
The function diagrams are divided up into a blue area A and two red areas B.
The blue area A represents the continuous range of the motor. Within this range the motor is able to run
continuously with optimum efficiency and operating life.
The two red areas B represent the intermittent range of the motor. It is advantageous to make use of theintermittent range when the motor works with varying loads, but also to allow for braking torques whenreversing direction.
It is permissible to subject the motor to intermittent speed or intermittent pressure drop for max. 10% of
every minute. The motor should not be subjected to intermittend speed and intermitend pressure dropat the same time.
The upper limits for intermittent pressure drop and torque must not be exceeded for more than 1% of
every minute (peak load). The max. peak load value is stated in the technical data for each type of motor.
High pressure peaks occur, for example, when a pressure relief valve opens or a directional valve is
opened or closed. Pressure relief valves and dual shock valves should be set so that pressure peaks do not
exceed the max. peak values. In systems with large pressure oscillations the pressure and torque peaks
should be measured with electronic equipment.
© Danfoss | December 2021

BC152886483554en-000401 | 13

Technical Information
General, Orbital Motors
Selection of Motor Size
To give problem-free operation the motor size should be selected using the permissible continuous andintermittent values while making sure that pressure peaks do not exceed the max. peak values.
Efficiency
The total efficiency ηt is the product of the volumetric efficiency (ηv) and the hydraulic-mechanicalefficiency (ηhm). Thus ηt = ηv x ηhm.
Volumetric efficiency
The volumetric efficiency is an expression for the proportion of the applied quantity of oil [as apercentage] that is converted to output shaft revolutions (speed). The remaining quantity of oil (leakage)is led across clearances and sealing surfaces to act as a lubricant/coolant.
When the load (pressure drop) increases, leakage also increases.
The quantity of oil supplied to the gearwheel set thus diminishes, and the number of revolution (speed)
falls.
in•lbs

Nm

Q1
Q2
4071

Q3

460

ηV

80 l/min[21.1 US gal/min]

Q1 = Qtotal
Q2 = Qtheor*
Q3 = Qleak

460

min-1
(rpm)
151-247.10

The slope of the Q-curve expresses the magnitude of the efficiency
ExampleAn OMT 160 is to drive a shaft at a speed of 460 min-1 (rpm) with an applied torque of 460 Nm [4071lbf•in].
If the volumetric efficiency was 100% the oil quantity would be the geometric displacement times thenumber of revolutions.
Theoretical supplied oil quantity:

However, the actual supplied oil quantity is 50 l/min [13.2 US gal]. The volumetric efficiency can becalculated as follows:

14 | © Danfoss | December 2021

BC152886483554en-000401

Technical Information
General, Orbital Motors
Selection of Motor Size

Hydraulic mechanical efficiency
The hydraulic mechanical efficiency is an expression for the proportion of applied pressure (as apercentage) that is converted to output shaft torque.
The remaining pressure is loss; either mechanical loss at low speeds or hydraulic loss at high speeds, as
can be seen on the torque graph (pressure-drop curve). Mechanical loss is greatest at motor start-up
because a film of lubricant has not yet been built up on moving parts. After a few revolutions the film isestablished and friction is reduced (the curve steepens). Hydraulic loss is greatest at high speeds becauseof the high pressure losses in ports and oil channels when oil flow is high. Therefore the pressure drop
across the gearwheel set becomes less and the motor yields less torque.
OMT 160 has a minimum starting torque of 340 Nm [3009 lbf•in] at a pressure drop of 200 bar [2900 psi],
as given in the OMT technical data table. When the lubricant film is established, the motor yields 460 Nm[4071 lbf•in] with the same pressure drop.
On the function diagram the pressure drop curve does not intersect the torque axis, but min. starting
torque at max. continuous and max. intermittent pressure drop is given in the technical data for each
motor type.
in•lbs

Nm

4539

513

4071

460

3009

340

ηm

ηh

460

200 bar2900 psi

min-1
(rpm)
151-248.10

Example:To calculate the hydraulic-mechanical efficiency ηhm, it is necessary to first read off (measure) the motor
torque Tmot eff for a given oil flow and given pressure drop. The function diagram efficiency graphs showthat an OMT 160 gives a torque of 460 Nm [4071 lbf•in] for a pressure drop of 200 bar [2900 psi] and an oil
flow of 80 l/min [21.1 US gal/min].
The theoretical motor torque for the same pressure drop can be calculated as follows:© Danfoss | December 2021

BC152886483554en-000401 | 15

Technical Information
General, Orbital Motors
Selection of Motor Size

Dividing the read-off (measured) torque by the theoretical torque gives the hydraulic-mechanicalefficiency:

Total efficiency
It is now possible to calculate the total efficiency of OMT 160 at ∆p = 200 bar [2900 psi] and Q = 80 l/min[21.1 US gal/min]:With an acceptable degree of accuracy the same total efficiency can be read from the function diagram
efficiency graphs.
Minimum speed
At very low speeds, the motors may run less smoothly. In borderline cases a motor of the desired typeshould be tested under the required operating conditions in the system concerned before finallyselecting the motor size and type.
To obtain smooth running at very low speed the motor leakage must be constant. Therefore it isrecommended that a motor with disc valve (OMT, OMV or TMT) be chosen, but avoid choosing motors
with the smaller displacements. The best results are achieved with a constant load, a return pressure of
3-5 bar [45-70 psi] and an oil viscosity of min. 35 mm2/s [164 SUS].

16 | © Danfoss | December 2021

BC152886483554en-000401

Technical Information
General, Orbital Motors
Bearing Dimensioning
Shaft load and bearing life time
In many applications the hydraulic motors must absorb both
• external radial and axial forces acting directly on the output shaft of the motor (e.g. from the weightof a vehicle)• radial forces produced by torque transfer from gearwheels, chainwheels, V-belts or winch drums.
For such applications hydraulic motors with built-in rolling bearings are particularly suitable. Two
different types of bearing are used in Danfoss hydraulic motors:
1. Needle bearings in WPN. The needle bearings are capable of absorbing large radial forces. As the
motors have separate axial bearings, the operating life of the needle bearings is not affected by thesize of the axial load.
2. Tapered roller bearings in OMT, OMTW, OMV, OMVW and TMT. The tapered roller bearings can absorb
large radial and axial forces.
The largest possible bearing capacity for the individual motor type is obtained by using OMTW or OMVW,
because the recessed mounting flange makes it possible to fit for example wheel hubs and winch drums
so that the radial load is applied centrally to the two bearings.
Motor with tapered roller bearings

Prad.

n

Pax.
151-1055.10

Relationship between Bearing Life Time and Speed
It is a general rule that life time and speed are inversely proportional: life is doubled when speed ishalved. So life can easily be calculated for other speeds than those given in the sections on shaft load in
the individual subcatalogues.
The relation is expressed by the formula:
Lnew = Lref x (nref / nnew)
where Lnew is the life time at speed nnew, and Lref and nref are the data for the given motor type found in
the subcatalogue.
Relationship between Shaft Load and Bearing Life Time
Lower shaft loads result in longer life time of the bearings. The exact relationship is shown by thefollowing formula:© Danfoss | December 2021

BC152886483554en-000401 | 17

Technical Information
General, Orbital Motors
Bearing Dimensioning
Lnew is the bearing life at a shaft load of Pnew, and Lref and nref are data from the subcatalogue.
Relationship between permissible shaft load and speed
In certain applications the motor must run at low speeds while the bearings must absorb high loads. Thisis the case for example when the motors are vehicle support elements. In such cases the following
relationship between speed and bearing load (with unchanged bearing life time) must be taken into
account:

Pnew is the shaft load at nnew. Pref and nref are data from the subcatalogue.
For nref = 200 min-1 [rpm] we have the following table forPnew / Pref:
nnew / min-1 (rpm)

25

50

100

200

300

400

500

600

700

Pnew / Pref

1.88

1.52

1.23

1.00

0.88

0.81

0.75

0.72

0.68

Maximum Radial Shaft Load
The calculations above are solely for bearing life time and load capacity. But there is also a limit to howmuch load the other parts of the motor (bearing housing, mounting flange and output shaft) can carry.
For this reason the maximum shaft load is limited to avoid the risk of mechanical breakdown.
The maximum shaft load is shown in the shaft load diagrams for OMT, OMV and TMT motors.
Please contact the Danfoss sales organisation for hydraulics if motors are to be subjected to shaft loads
higher than the maximum, or where there are particularly high dynamic effects (shock factor > 3).

18 | © Danfoss | December 2021

BC152886483554en-000401

Technical Information
General, Orbital Motors
Hydraulic Systems
Max. Pressure on the Shaft Seal
Danfoss hydraulic motors can be supplied fitted with one of three different shaft seals:
Standard shaft seal (NBR)
The standard shaft seal in Danfoss hydraulic motors has a long operating life and even under extreme
conditions retains its sealing capability. With optimal lip design, the shaft seal withstands both highpressures and high speeds.
High-pressure shaft seal (NBR)
The high-pressure shaft seal (HPS) is a development of our standard shaft seal and the integrated backing
ring makes an external drain line superfluous in most operating conditions.
Viton shaft seal (FPM)
If a synthetic fluid is to be used in our hydraulic motors we recommend a Viton shaft seal.
Characteristics of sealing materials
Material

Temperature ˚C [˚F]

Remarks

NBR-30 to + 100[-22 to 212]

Swells up on contact with most syntetic fluids
Can be used with Emulsions and Mineral oils

FPM

-30 to + 150[-22 to 302]

Ideal for mineral oil, synthetic fluids andemulsions

All Danfoss motors, except the OMEW, are 3-cham-ber type of motors, i.e. this type og motor isolates thehigh pressure from the case, which allows the use of an external drain when return line pressure isexcessive. These motors are offered with the following option:

Motors with check valve
The check valve means that the pressure on the shaft seal never exceeds the pressure in the return line. If
the motor contains check valves and there is no drain line, the motor return pressure must always be lessthan or equal to the maximum permissible pressure on the shaft seal graph in the subcatalogue.

151-1803.10

Motors with drain line
The drain line relieves the pressure on the shaft seal to tank. That is to say, the tank pressure must be lessthan or equal to the max. permissible pressure on the shaft seal graph in the subcatalogue.

151-1807.10© Danfoss | December 2021

BC152886483554en-000401 | 19

Technical Information
General, Orbital Motors
Hydraulic Systems
Motors without check valve and drain line
The pressure on the shaft seal is equal to the average of the inlet pressure and return pressure:
Pseal = (Pinlet + Preturn) / 2
Pseal must be less than or equal to the max. permissible pressure on the shaft seal graph in thesubcatalogue.

151-1743.10

Short/ultra-short motors
For these motors it is the values of the pressure on the shaft seal in connected component (e.g. a gear)that applies.

151-1743.10

Drain Line
Application
The drain line relieves pressure on the shaft seal to tank. The following main rules apply to drain lines
fitted to Danfoss hydraulic motors:• We recommend a drain line when the maximum pressure on the shaft seal is exceeded, i.e. the life of
the shaft seal can otherwise be significantly reduced.
• We always recommend a drain line when
‒ a short motor is built together with a gear.

‒ the motor is used in hydrostatic transmissions that do not have a separate flushing valve.

Oil flow in the drain line
When the size of the supply pump in a closed hydraulic circuit is to be calculated, it is necessary to know
the maximum oil flow in the drain line. The maximum oil flow in the drain line for Danfoss hydraulicmotors is given in the technical data in the catalogue for each motor type.
Braking
Danfoss hydraulic motors are often used to brake a load. Here the motors operate as pumps that convert
the kinetic energy of the load (mass, speed) to hydraulic energy (oil flow, pressure). Examples of thesetypes of applications are:
• Crane winches on vehicles•••
20 | © Danfoss | December 2021

Net winches on fishing vessels
Top jib slewing on cranes and excavators
Hydrostatic transmissions
BC152886483554en-000401

Technical Information
General, Orbital Motors
Hydraulic Systems
The speed at which the load is braked is determined by the motor braking torque and the openingpressure of the dual shock valve.
Braking torqueWith a motor, the hydraulic-mechanical efficiency means that the effective torque is lower than thetheoretical torque.
Tmotor eff = Ttheor x ηhm (1)With a pump, the hydraulic-mechanical efficiency means that the effective torque that must be applied
to the pump to create a given pressure drop is greater than the theoretical pressure drop.
Tpump eff = Ttheor / ηhm (2)When a hydraulic motor is used as a pump (for braking) the ratio between braking torque and effective
motor output for a given pressure drop is as follows:
Tbrake = Ttheor / ηhm (see 2) where
Ttheor = Tmotor eff / ηhm (see 1)
Tbrake = Tmotor eff / (ηhm)2
We recommend the use of the following braking torques for Danfoss hydraulic motors:• OMT, OMV,TMT : Tbrake ~ 1.2 · Tmotor eff.
Tmotor eff can be read from the function diagram for the individual motor sizes.
The braking torque must not be greater than the maximum motor operating torque.
The maximum torque is given in the technical data for each motor type.
Opening pressure for the dual shock valve
The braking torque can be regulated by setting the opening pressure of the dual shock valve. The
opening pressure should be set at max. oil flow, in that a 20-30% increase in opening pressure can be
expected when the oil flow is changed from minimum to maximum.
To avoid excessive pressure peaks, the dual shock valve should be rapid acting and be installed as close
to the hydraulic motor as possible.
Replenishment
When Danfoss hydraulic motors are used to brake a load, effective replenishment is necessary.
Inadequate replenishment can give rise to:• cavitation in the gearwheel set•

insufficient braking capacity

There must therefore be positive charge pressure in the motor "suction" port.
The charge pressure (ps) must therefore be greater than the pressure drop in the motor oil channels
feeding the gearwheel set.
The pressure drop in the oil channels depends on the motor type, oil flow and oil viscosity. The pressure
drop graphs for each motor type are given in the respective catalogues.
The supply pressure should constitute half the pressure drop (pd) given on the graph:
ps = p d / 2
The charge pressure is always measured at the motor "suction" port.
In closed circuits the supply pressure will always be positive when the system is fitted with a charge
pump (ps ~ 10-15 bar [145-217 psi]).
In open systems where the hydraulic motor drives a load with high inertia, it is necessary to establish
replenishment as shown in fig. 1.
© Danfoss | December 2021

BC152886483554en-000401 | 21

Technical Information
General, Orbital Motors
Hydraulic Systems
The opening pressure of the check valve must be greater than the sum of the charge pressure (ps) andthe pressure drop between check valve and motor "suction" port.
Fig. 1

151-122.10

C: Shock valve
D: Pressure relief valve
E: Spring-loaded
check valve
Special conditions apply to open circuits where the hydraulic motor drives a load with high inertia. Whenthe directional valve changes from I to II, the oil flow from pump to motor is shut off.
Load inertia will continue to drive the pump and for the same reasons as above a check valve should beinstalled to ensure replenishment, otherwise oil will be emptied from the motor see fig. 2.

22 | © Danfoss | December 2021

BC152886483554en-000401

Technical Information
General, Orbital Motors
Hydraulic Systems

151-1142.10

Seeping
To prevent the load from moving during long periods, two precautions must be taken:
1. If the motor has a drain line it is necessary to ensure replenishment, otherwise oil will be graduallyemptied from the gearwheel set and the load will fall freely. The best method is shown in fig.
2. A orbital motor cannot retain a load in a given position without movement. Internal leakage [seeping]in the motor will result in the load moving. Therefore, with hydrostatic transmissions, with craneslewing and with winches and hanging loads, Danfoss motors with integral holding brakes should be
used.
Alternatively, the drive shaft should be equipped with an external holding brake see fig. 3.
Fig. 3Pr
151-1143.10

Brake Motors
Danfoss OMS, OMT and TMT motors are available with integrated brake:© Danfoss | December 2021

BC152886483554en-000401 | 23

Technical Information
General, Orbital Motors
Hydraulic Systems•

OMT FX, OMT FL, TMT FL and OMT FH with spring-activated multidisc brake released by hydraulicpressure.

A

C

M

D

151-1404.10

A: Brake motor
C: Brake release port
D: Drain connection
M: Directional valve
O: Charge pump
OMT FX, OMT FL and TMT FL
These motors are suitable for hydrostatic transmissions and other closed circuits.
- the supply charge pump pressure is sufficient to release the brake.
The directional valve (M) can be coupled to the vehicle controls so that the brake pressure is
automatically released to tank when the vehicle stops.
OMT FH
These motors are designed for open circuits and withstands max. system pressure in the brake releaseline, even when the brake is released at low pressure. Brake release can be controlled by connecting therelease port to the pump line.
In addition, either a changeover valve can be installed to give automatic brake release or a directional
valve to control brake release.

24 | © Danfoss | December 2021

BC152886483554en-000401

Technical Information
General, Orbital Motors
Hydraulic Systems

C
A
P

D

151-1462.10

A: Brake motor
C: Brake release port
D: Drain connection
P: Shuttle valve
Brake motors must always have a drain line

Installation, Starting Up, Maintenance and Oil Types
Design in brief•••

To ensure optimum operation all hydraulic components must be installed in accordance with theirindividual instructions.
The pump line must contain a pressure gauge connection.
To ensure correct joint contact and minimise material stress, all mounting flanges must be plane.
Hydraulic lines must be installed correctly to avoid air pockets inside them.

Combination in brief

•
•
•
•
•
•
•

Hydraulic components must be installed in accordance with their individual instructions.
To avoid contamination, plastic plugs in connection ports must not be removed until just before
connections are made.
There must be full contact between motor mounting flange and connecting part.
Avoid pressing the motor into place by tightening the fixing bolts.
Avoid unsuitable seal materials, e.g. twine, teflon, etc., on threaded unions. Use only the seals
supplied, such as O-rings, steel washers, etc.
When tightening unions, never use more torque than the max. values given in instructions.
Check to make sure the purity of the oil is better than 20/16 (ISO 4406) and always use a filter whenreplenishing the system.

Starting up and running in the hydraulic system

•
•
•
•

© Danfoss | December 2021

Pour the oil through a fine-mesh filter and fill up the tank to the top level mark.
Start the drive motor and allow it to run at its lowest speed, if possible. If the motor has bleed screws,
allow them to remain open until the oil no longer foams.
Check to make sure that all components are correctly connected (and that the pump runs in thecorrect direction, etc.).
If a load-sensing system is involved, make sure there is no air in the signal lines.

BC152886483554en-000401 | 25

Technical Information
General, Orbital Motors
Hydraulic Systems
Signs of air in the hydraulic system•••

Foam in the tankJerky movements of motor and cylinder
Noise

If there is air in the system

•
•
•
•
•

Replenish the oil.
Connect the system to a separate tank with filter (filter mesh max. 10 µm). The tank capacity must be
twice the max. oil flow. Allow the system to run without load [no pressure] for around 30 minutes.
Do not load the system until it has been completely bled and is clean.
Check for system leakage and make sure it operates satisfactory.
Replace the oil filter and, if necessary, replenish the oil.

During operation••

Do not subject the motor to pressure, pressure drop or speeds exceeding the maximum values statedin the appropriate catalogues.
Filter the oil to maintain the grade of contamination at 20/16 (ISO 4406) or better.

Maintenance

•
•
•
•

With hydraulic systems the main criterion for reliability and operating life is very
thorough maintenance.
Replenish and change the oil, the oil and air filters as stated in the respective
instructions.
Regularly check the condition of the oil, system leakage and the oil level.

Oil Types
In a hydraulic system the most important task of the oil is to transfer energy. At the same time the oilmust lubricate moving parts in hydraulic components, protect them from corrosion, and conduct dirt
particles and heat out of the system. To ensure that the hydraulic components operate without problems
and have a long operating life it is therefore vital to select the correct oil type with the necessary
additives.

Mineral oils
For systems containing Danfoss hydraulic motors, we recommend mineral hydraulic oil with anti-wear
additives, type HLP [DIN 51524] or HM (ISO 6743/4). Mineral oils without anti-wear additives or engine
oils can also be used, provided operating conditions are suitable.
If oil types that have not been classified are being considered, please contact the Danfoss Sales
Organisation.

Non-flammable or biodegradable fluids
Danfoss hydraulic motors can also be used in systems with non-flammable or biodegradable fluids.
However, the function and life of the motor will depend on the type and condition of the fluid used. To
achieve satisfactory operation and life it is therefore necessary to match the operating conditions to theproperties of the fluid used.
Before using non-flammable or biodegradable fluids we recommend contact with the Danfoss Sales
Organisation.

26 | © Danfoss | December 2021

BC152886483554en-000401

Technical Information
General, Orbital Motors
Hydraulic Systems
Temperature, Viscosity and Filtering
Temperature
Ambient temperature should lie between -30°C [-22 °F ] and +90°C [+210°F] to ensure that the shaft sealretains its sealing capacity.
Oil temperature should lie between +30°C [+85°F] and +60°C [+140°F] during normal operation. Oil life isgreatly reduced if its temperature exceeds +60°C [+140°F]. As a general rule, oil life is halved for each 8°C[15°F] its temperature exceeds 60°C [+140°F].
Viscosity
The viscosity of the oil should lie between 20 mm2/s and 75 mm2/s [100 and 370 SUS] when theoperating temperature of the system has become stabilised. We recommend the use of an oil type
having a viscosity of 35 mm2/s [165 SUS] at the actual operating temperature.
SUS

mm 2/₃50,00010,00020,0005,000

10,000

2,500

4,000

1,000
800

2,000

500

1,000

250

500

100
75
50

200

C
25

100

20

70
10
50
45

6
5

40

36

3

34.5

2.5

D
-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

80 90 100 110

-58

-40

-22

-4

14

32

50

65

85

105

125 140 155 175 195 212 220

˚C
˚F

151-1321.10

C: Recommended viscosity range
D: Recommended temperatu range© Danfoss | December 2021

BC152886483554en-000401 | 27

Technical Information
General, Orbital Motors
Hydraulic Systems
Filtering
It is necessary to keep the level of oil contamination at an acceptable level to ensure problem-free
operation. The recommended maximum level of contamination in systems with Danfoss hydraulicmotors is 20/16 (see ISO 4406*). In our experience the 20/16 contamination level can be met by using a
return filter finer than 40 µm absolute or 25 µm nominal. In very dirty environments, in complex systems,
and in closed circuits, the recommended filtration level is 20 µm absolute or 10 µm nominal.
(In systems with quick release couplings a pressure filter having a fineness of 40 µm absolute should be
inserted just ahead of the motor).

28 | © Danfoss | December 2021

BC152886483554en-000401

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 | December 2021

BC152886483554en-000401