Series 40 Family of Pumps and Motors.....................................................................................................................................7
Case Pressure...................................................................................................................................................................................10
Redundant Braking System Requirement.............................................................................................................................14
Case Drain usage for Tandem Pumps.....................................................................................................................................15
Bearing Life and External Shaft Loading ...............................................................................................................................15
Hydraulic Unit Life......................................................................................................................................................................... 16
Model Code......................................................................................................................................................................................19
Charge Pump Power Requirements........................................................................................................................................22
M25 Tandem Pump.......................................................................................................................................................................28
M35/44 Tandem Pump................................................................................................................................................................ 30
Direct Displacement Control (DDC)........................................................................................................................................ 31
External control handle requirements..............................................................................................................................31
M25 Tandem Pump.......................................................................................................................................................................35
M35/44 Tandem Pump................................................................................................................................................................ 39
Single Pump Schematics.............................................................................................................................................................42
Tandem Pump Schematics.........................................................................................................................................................43
Product lineSeries 40 Pumps
Pump typeIn-line, axial piston, variable, positive displacement pumps
Direction rotationClockwise (CW) or counterclockwise (CCW) available
Installation positionDiscretionary, the housing must be filled with hydraulic fluid
Filtration configurationSuction or charge pressure filtration
Other system requirementsIndependent braking system, suitable reservoir and heat exchanger
Series 40 is a family of hydrostatic pumps and motors for medium power applications with maximum
loads of 345 bar [5000 psi]. These pumps and motors can be applied together or combined with other
products in a system to transfer and control hydraulic power.
Series 40 pump + motor transmissions provide an infinitely variable speed range between zero and
maximum in both forward and reverse modes of operation. The pumps and motors each come in four
frame sizes: M25, M35, M44, and M46.
Series 40 pumps are compact, high power density units. All models use the parallel axial piston / slipper
concept in conjunction with a tiltable swashplate to vary the pump’s displacement. Reversing the angle
of the swashplate reverses the flow of fluid from the pump, reversing the direction of rotation of the
motor output.
Series 40 - M35 and M44 pumps may include an integral charge pump to provide system replenishing
and cooling fluid flow. M25 pumps are designed to receive charge flow from an auxiliary circuit or from a
gear pump mounted on the auxiliary mounting pad. Series 40 pumps feature a range of auxiliary
mounting pads to accept auxiliary hydraulic pumps for use in complementary hydraulic systems.
For complete technical information on M46 pumps, refer to M46 Pumps Technical Information, L1001029.
Series 40 motors use the parallel axial piston/slipper design in conjunction with a fixed or tiltable
swashplate. The family includes M25, M35, M44 fixed motor units and M35, M44, M46 variable motor
units. For complete technical information on Series 40 motors, refer to Series 40 Motors TechnicalInformation, 520L0636.
The M35 and M44 variable motors feature a trunnion style swashplate and direct displacement control.
The M46 variable motors use a cradle swashplate design and a two-position hydraulic servo control.
The M46 variable motor is available in a cartridge flange version, which is designed to be compatible with
CW and CT compact planetary gearboxes. This combination provides a short final drive length for
applications with space limitations.
Danfoss | July 2017520L0635 | BC00000106en-US0703 | 7
Input
shaft
Auxiliary
pad
Trunnion
Charge check and
high pressure relief
valve with bypass
Charge relief
valve
Charge
pump
Swashplate
Cylinder
block
Ball
bearing
Valve plate
Piston
P100 584E
S
M3
A
B
M2
M1
L1
E
L2
EE
D
No relief valve
Suction Filtration
Remote Pressure Filtration
Remote pressure filtration
(no charge pump)
P100 638E
Technical Information
Series 40 Direct Displacement Pumps
General Information
M35 Variable Pump (M44 is similar)
A variable pump is shown in a hydraulic circuit with a fixed motor. The pump shown features manual
displacement control. The circuit features suction filtration and heat exchanger.
High Pressure Relief Valve (HPRV) - A high pressure relief valve limits the system pressure to protect
the system from over-pressure.
Charge Relief Valve - The charge pressure relief valve regulates charge pressure.
Displacement Limiters - Optional displacement limiters allow maximum displacement adjustment to
allow for fine tuning of the propel system.
Auxiliary Mounting Pads - Several auxiliary mounting pad options allow for adding a second pump.
Input Shafts - Straight keyed, tapered keyed, and several splined shaft options are available.
Danfoss | July 2017520L0635 | BC00000106en-US0703 | 9
Technical Information
Series 40 Direct Displacement Pumps
Operating Parameters
Fluids
Ratings and performance data are based on operating with premium hydraulic fluids containing
oxidation, rust, and foam inhibitors. These include premium turbine oils, API CD engine oils per SAE J183,
M2C33F or G automatic transmission fluids (ATF), Dexron II (ATF) meeting Allison C-3 or Caterpillar T0‑2
requirements, and certain specialty agricultural tractor fluids. For more information on hydraulic fluid
selection, see Danfoss publications: Hydraulic Fluids and Lubricants, Technical Information, 520L0463 and,
Experience with Biodegradable Hydraulic Fluids, Technical Information,520L465.
Viscosity
Maintain fluid viscosity within the recommended range for maximum efficiency and bearing life.
Minimum viscosity is acceptable only during brief occasions of maximum ambient temperature and
severe duty cycle. Maximum viscosity is acceptable only at cold start: Limit speeds until the system warms
up. See Danfoss publications: Hydraulic Fluids and Lubricants, Technical Information, 520L0463, and
Experience with Biodegradable Hydraulic Fluids, Technical Information, 520L465.
Fluid viscosity limits
Conditionmm2/s (cSt)SUS
Minimum747
Continuous12-6070-278
Maximum16007500
Temperature
Charge Pressure
Case Pressure
Maintain fluid temperature within the limits shown in the table. Minimum temperature relates to the
physical properties of the component materials. Cold oil will not affect the durability of the motor
components. However, it may affect the ability of the motor to transmit power. Maximum temperature
is based on material properties: Don’t exceed it. Measure maximum temperature at the hottest point in
the system. This is usually the case drain.
Ensure fluid temperature and viscosity limits are concurrently satisfied.
Temperature limits
Minimum (intermittent, cold start)- 40° C [- 40° F]
Continuous82.2° C [180° F]
Maximum104.4° C [220° F]
All systems require a charge (positive pressure) in the low side of the system loop for proper lubrication
and rotating group operation. Maintain low loop (charge) pressure at a minimum of 6 bar [87 psi] above
case pressure.
Maintain case pressure within the limits shown in the table. Ensure housing is filled with hydraulic fluid.
Case pressure limits
Maximum (continuous)1.7 bar [25 psi]
Intermittent (cold start)5.2 bar [75 psi]
Operating outside of charge and case pressure limits will damage the pump. To minimize this risk, use full
size inlet and case drain plumbing, and limit line lengths.
Pressure Ratings
System pressure is the differential pressure between high pressure system ports. It is the dominant
operating variable affecting hydraulic unit life. High system pressure, which results from high load,
reduces expected life. Hydraulic unit life depends on the speed and normal operating, or weighted
average, pressure that can only be determined from a duty cycle analysis.
Application pressure is the high pressure relief or pressure limiter setting normally defined within the
order code of the pump. This is the applied system pressure at which the driveline generates the
maximum calculated pull or torque in the application.
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 is the highest allowable application pressure under any circumstance. Application
pressures above maximum working pressure will only be considered with duty cycle analysis and factory
approval.
Minimum low loop pressure must be maintained under all operating conditions to avoid cavitation.
Speed Ratings
Inlet Pressure
All pressure limits are differential pressures referenced to low loop (charge) pressure. Subtract low loop
pressure from gauge readings to compute the differential.
The table, Operating Parameters in the Specifications section, gives rated and maximum speeds for each
displacement. Not all displacements operate under the same speed limits. Definitions of these speed
limits appear below.
Continuous speed is the maximum recommended operating speed at full power condition. Operating at
or below this speed should yield satisfactory product life. Do not exceed maximum motor speed during
unloaded, on-road travel over level ground.
Maximum speed is the highest operating speed permitted. Exceeding maximum speed reduces pump
life and can cause loss of hydrostatic power and braking capacity. Never exceed the maximum speed
limit under any operating conditions.
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 the
hydrostatic transmission, sufficient to stop and hold the vehicle or machine in the event of hydrostatic
drive power loss.
Achieving acceptable pump life and performance requires proper charge pump inlet design. A
continuous inlet pressure of not less than 0.8 bar abs. (not more than 6.3 in. Hg vac.) is recommended.
Normal pressure less than the minimum inlet pressure of 0.7 bar abs. (greater than 9.2 in. Hg vac.)
indicates inadequate inlet design or a restricted filter. Pressures less than 0.7 bar abs. (greater than 9.2 in.
Hg vac.) during cold start are possible, but should improve quickly as the fluid warms.
Danfoss | July 2017520L0635 | BC00000106en-US0703 | 11
Technical Information
Series 40 Direct Displacement Pumps
Operating Parameters
Inlet pressure
Continuous0.86
Minimum0.79.2 (max)
Theoretical Output
The theoretical maximum flow at rated speed is a simple function of pump displacement and speed. This
is a good gauge for sizing a companion motor. This does not take into account losses due to leakage or
variations in displacement.
Use these equations to help choose the right pump size and displacement for your application.
Variables
SI units [US units]
Vg = Displacement per revolution cm3/rev [in3/rev]
pO = Outlet pressure bar [psi]
pi = Inlet pressure bar [psi]
∆p = pO - pi (system pressure) bar [psi]
n = Speed min-1 (rpm)
ηv = Volumetric efficiency
ηm = Mechanical efficiency
ηt = Overall efficiency (ηv • ηm)
Filtration
Ensure fluid entering pump is free of contaminants to prevent damage (including premature wear) to the
system. Series 40 pumps require system filtration capable of maintaining fluid cleanliness at ISO
4406-1999 class 22/18/13 or better.
Consider these factors when selecting a system filter:
Cleanliness specifications
•
Contaminant ingression rates
•
Flow capacity
•
Desired maintenance interval
•
Locate filter either on the inlet (suction filtration) or discharge (charge pressure filtration) side of the
charge pump. Series 40 pumps are available with provisions for either strategy.
Typically, a filter with a beta ratio of β10 = 1.5 to 2.0 is adequate. However, open circuit systems supplied
from a common reservoir may have considerably higher requirements. Because each system is unique,
only a thorough testing and evaluation program can fully validate the filtration system. For more
information, see Danfoss publication Design Guidelines for Hydraulic Fluid Cleanliness, 520L0467.
Suction filtration
The suction filter is placed in the circuit between the reservoir and the inlet to the charge pump as shown
in the accompanying illustration.
Danfoss | July 2017520L0635 | BC00000106en-US0703 | 13
Reservoir
Filter
Charge
pump
Charge relief
valve
To pump case
To low pressure
side of loop
and servo control
Strainer
P100 588E
Reservoir
Filter
with bypass
Charge
pump
Charge relief
valve
To pump case
To Low Pressure
side of loop
and servo control
Strainer
P106 102E
W
Technical Information
Series 40 Direct Displacement Pumps
System Design Parameters
Suction filtration
Charge filtration
Provision for charge pressure filtration is available on all Series 40 pumps. The pressure filter is remotely
mounted in the circuit after the charge pump, as shown in the accompanying illustration.
Filters used in charge pressure filtration circuits must be rated to at least 34.5 bar [500 psi] pressure. A 100
- 125 µm screen located in the reservoir or in the charge inlet line is recommended when using charge
pressure filtration.
A filter bypass valve is necessary to prevent filter damage and to avoid contaminants from being forced
through the filter media by high pressure differentials across the filter. In the event of high pressure drop
associated with a blocked filter or cold start-up conditions, fluid will bypass the filter. Avoid working with
an open bypass for an extended period. We recommend a visual or electrical bypass indicator. Proper
filter maintenance is mandatory.
Charge filtration
Redundant Braking System Requirement
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 the