ASTM D7721-22

Standard Practice for Determining the Effect of Fluid Selection on Hydraulic System or Component Efficiency

SIGNIFICANCE AND USE
5.1 The primary function of a hydraulic fluid is to transmit power. This practice provides uniform guidelines for comparing fluids in terms of their power-transmitting abilities as reflected in their effect on hydraulic system or component efficiency and productivity.  
5.2 Practical advantages of enhanced hydraulic system efficiency may include increased productivity (faster machine cycle time), reduced power consumption (electricity or fuel), and reduced environmental impact (lower emissions).  
5.3 Differences in fluid performance may be relatively small. Consequently, it is essential that the necessary experimental controls are implemented to ensure consistency in operating conditions and duty cycle when comparing the energy efficiency of different hydraulic fluid formulations.  
5.4 This practice implies no evaluation of hydraulic fluid quality other than its effect on hydraulic system efficiency.
SCOPE
1.1 This practice covers all types and grades of hydraulic fluids.  
1.2 This practice is applicable to both laboratory and field evaluations.  
1.3 This practice provides guidelines for conducting hydraulic fluid evaluations. It does not prescribe a specific efficiency test methodology.  
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.  
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.  
1.6 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.

General Information

• Status: Published
• Publication Date: 31-Aug-2022
• ICS: 75.120 - Hydraulic fluids
• Technical Committee: D02 - Petroleum Products, Liquid Fuels, and Lubricants
• Drafting Committee: D02.N0 - Hydraulic Fluids

Relations

• Refers: ASTM D4175-23a - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 15-Dec-2023
• Refers: ASTM D4175-23e1 - Standard Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• Effective Date: 01-Jul-2023
• Refers: ASTM D4174-15 - Standard Practice for Cleaning, Flushing, and Purification of Petroleum Fluid Hydraulic Systems
• Effective Date: 01-Apr-2015
• Refers: ASTM D4174-89(2010) - Standard Practice for Cleaning, Flushing, and Purification of Petroleum Fluid Hydraulic Systems
• Effective Date: 01-Oct-2010
• Refers: ASTM D4174-89(2005) - Standard Practice for Cleaning, Flushing, and Purification of Petroleum Fluid Hydraulic Systems
• Effective Date: 01-May-2005
• Refers: ASTM D4174-89(1999) - Standard Practice for Cleaning, Flushing, and Purification of Petroleum Fluid Hydraulic Systems
• Effective Date: 10-Apr-1999

Overview

ASTM D7721-22: Standard Practice for Determining the Effect of Fluid Selection on Hydraulic System or Component Efficiency provides a structured approach for comparing hydraulic fluids based on their impact on the efficiency of hydraulic systems and components. Developed by ASTM International, this standard assists manufacturers, laboratory personnel, and field operators in reliably evaluating and comparing different hydraulic fluid formulations, ensuring accurate measurement of efficiency improvements across diverse applications.

Key Topics

• Purpose and Significance: The main function of hydraulic fluids is to transmit power. This practice outlines uniform guidelines for evaluating fluids based on their effect on hydraulic system and component efficiency.
• Efficiency Measurement: The standard ensures that practical differences in fluid performance are detected through controlled laboratory or field testing, employing appropriate statistical methods.
• Testing Guidelines:
  • Applicable to all types and grades of hydraulic fluids.
  • Covers laboratory and real-world field evaluations.
  • Does not prescribe specific test methods but emphasizes principles of consistency, validity, and fair comparison.
  • Mandates proper experimental setup, including statistical design, control over test variables, and meticulous data collection.
• Environmental and Operational Benefits: Enhanced hydraulic efficiency can lead to increased productivity (faster cycles), reduced energy and fuel consumption, and lower environmental emissions.
• Scope Limitations: This standard focuses strictly on efficiency effects, without evaluating overall fluid quality.

Applications

• Hydraulic Equipment Development: OEMs and research laboratories can use this practice to select or develop hydraulic fluids that maximize operational efficiency for pumps, motors, and hydraulic circuits.
• Industrial Operations: Field operators can benchmark fluid efficiency in equipment such as excavators, loaders, presses, and injection molding machines, leading to informed maintenance and fluid replacement decisions.
• Productivity and Sustainability: By identifying fluids that offer efficiency gains, organizations can achieve faster machine operation cycles, reduced power/fuel costs, and improved sustainability through lower environmental impact.
• Quality Assurance and Procurement: Fluid manufacturers and purchasers benefit from standardized criteria when specifying or procuring hydraulic fluids for efficiency-critical applications.

Related Standards

The following standards are commonly referenced with ASTM D7721-22 and provide complementary guidance:

• ASTM D4174: Practice for Cleaning, Flushing, and Purification of Petroleum Fluid Hydraulic Systems
• ASTM D4175: Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
• ISO 4391: Hydraulic fluid power - Pumps, motors, and transmissions - Parameter definitions
• ISO 4392-1: Determination of characteristics of motors at low speed and constant pressure
• ISO 4409: Methods of testing and presenting steady-state performance of positive-displacement pumps, motors, and transmissions
• ISO 5598: Fluid power systems and components - Vocabulary
• ISO 8426: Determination of derived capacity for pumps and motors
• VDI 2198: Type sheets for industrial trucks

Practical Value

ASTM D7721-22 enables stakeholders to evaluate and compare the efficiency effects of hydraulic fluids in a controlled, reliable, and repeatable manner. This structured approach supports:

• Data-driven selection of hydraulic fluids for both new and existing hydraulic systems.
• Documented improvements in energy efficiency and reduced operational costs.
• Contributions to sustainability objectives by lowering energy use and emissions.
• Alignment with international best practices and terminology, improving global industry compatibility and fluid standardization efforts.

By following this standard, organizations can make confident, evidence-based decisions that yield tangible operational and environmental benefits in hydraulic system management.

Standards Content (Sample)

This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the
Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
Designation: D7721 − 22
Standard Practice for
Determining the Effect of Fluid Selection on Hydraulic
System or Component Efficiency
This standard is issued under the fixed designation D7721; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope* 2.2 ISO Standards:
ISO 4391 Hydraulic fluid power—Pumps, motors and inte-
1.1 This practice covers all types and grades of hydraulic
gral transmissions—Parameter definitions and letter sym-
fluids.
bols
ISO 4392–1 Hydraulic fluid power—Determination of char-
1.2 This practice is applicable to both laboratory and field
acteristics of motors—Part 1: At constant low speed and
evaluations.
constant pressure
1.3 This practice provides guidelines for conducting hy-
ISO 4409 Hydraulic fluid power—Positive-displacement
draulic fluid evaluations. It does not prescribe a specific
pumps, motors and integral transmissions—Methods of
efficiency test methodology.
testing and presenting basic steady state performance
ISO 5598 Fluid power systems & components—Vocabulary
1.4 The values stated in SI units are to be regarded as
ISO 8426 Hydraulic fluid power—Positive displacement
standard. No other units of measurement are included in this
pumps and motors—Determination of derived capacity
standard.
1.5 This standard does not purport to address all of the 3. Terminology
safety concerns, if any, associated with its use. It is the
3.1 For additional definitions related to petroleum products
responsibility of the user of this standard to establish appro-
and lubricants, see Terminology D4175. For additional defini-
priate safety, health, and environmental practices and deter-
tions related to fluid power systems and components, see ISO
mine the applicability of regulatory limitations prior to use.
5598.
1.6 This international standard was developed in accor-
3.2 Definitions:
dance with internationally recognized principles on standard-
3.2.1 baseline oil, n—oil of known performance character-
ization established in the Decision on Principles for the
istics used as a basis for comparison.
Development of International Standards, Guides and Recom-
3.2.1.1 Discussion—For purposes of this practice, the base-
mendations issued by the World Trade Organization Technical
line oil may be a hydraulic fluid of any suitable composition.
Barriers to Trade (TBT) Committee.
3.2.2 component, n—of a hydraulic system, an individual
unit, excluding piping, comprising one or more parts designed
2. Referenced Documents
to be a functional part of a fluid power system, for example,
2.1 ASTM Standards:
cylinder, motor, valve, or filter.
D4174 Practice for Cleaning, Flushing, and Purification of
3.2.3 critical parts, n—those components used in the test
Petroleum Fluid Hydraulic Systems
that are known to affect test severity.
D4175 Terminology Relating to Petroleum Products, Liquid
3.2.4 cycle time, n—the amount of time it takes for a
Fuels, and Lubricants
machine to perform a repetitive segment of an operation,
typically measured as the time it takes a machine to return to
the original position after completing a task.
This practice is under the jurisdiction ofASTM Committee D02 on Petroleum
3.2.5 energy consumption, n—the total energy content con-
Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcom-
sumed during a test in kWh; determined from electric power
mittee D02.N0 on Hydraulic Fluids.
Current edition approved Sept. 1, 2022. Published October 2022. Originally
meter readings or calculated from the mass of fuel consumed
approved in 2011. Last previous edition approved in 2017 as D7721 – 17.
and the lower heating value of the fuel.
DOI:10.1520/D7721-22.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Available from International Organization for Standardization (ISO), ISO
Standards volume information, refer to the standard’s Document Summary page on Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier,
the ASTM website. Geneva, Switzerland, http://www.iso.org.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7721 − 22
3.2.6 energy effıciency, n—the work output divided by the 3.3.3.1 Discussion—The power factor is the dimensionless
energy input; this ratio may be expressed as a percentage. ratio of energy used compared to the energy flowing through
the wires.
3.2.7 fit for use, n—product, system, or service that is
3.3.4 system overall effıciency, n—in fluid power systems,
suitable for its intended use.
the ratio of the output power of the system to the input power
3.2.8 fuel rate, n—the rate at which fuel is consumed in L/h,
of the system.
normalized to the fuel density at 15 °C.
3.3.4.1 Discussion—For integral transmissions and open-
3.2.9 grade, n—designation given a material by a manufac-
loop hydraulic circuits that drive a hydraulic motor, system
turer so that it is always reproduced to the same specifications
overall efficiency is the ratio of the output mechanical power at
established by standards organizations such as ASTM or ISO.
the hydraulic motor shaft to the input mechanical power at the
3.2.10 hydraulic fluid, n—liquid used in hydraulic systems
pump shaft. Methods ISO 4391 and ISO 4409 provide addi-
for lubrication and transmission of power.
tional details for determining system efficiency in circuits with
3.2.11 hydraulic system, n—fluid power system that is an
boost pumps.
arrangement of interconnected components which generates,
transmits, controls, and converts fluid power energy.
4. Summary of Practice
3.2.12 motor hydromechanical effıciency, n—ratio of the
4.1 The purpose of this practice is to define minimum
actual torque output of the motor to the theoretical torque
technicalrequirementsforconductingenergyefficiencyperfor-
output of the motor.
mance comparisons of two or more hydraulic fluids in con-
trolled laboratory or field evaluations. It is organized in three
3.2.13 motor overall effıciency, n—ratio of the mechanical
sections.
output power to the power transferred from the liquid at its
passage through the motor.
4.2 Thefirstsectiondescribesguidelinesforadynamometer
evaluation of fluids in a high-pressure positive displacement
3.2.14 motor volumetric effıciency, n—ratio of the theoreti-
pump. Baseline and test fluids are evaluated under steady-state
cal inlet flow rate to the effective inlet flow rate.
conditions of pump shaft speed, displacement, outlet pressure
3.2.15 outlier, n—result far enough in magnitude from other
and fluid temperature. Input torque, outlet flow and case drain
results to be considered not part of the set.
flow rates are measured.
3.2.15.1 Discussion—For purposes of this practice, classifi-
4.3 The second section describes guidelines for dynamom-
cation of a result as an outlier shall be justified by statistical
eter evaluation of fluids in low-speed hydraulic motor testing.
criteria in comparison with the valid data points.
Baseline and test fluids are evaluated under steady-state
3.2.16 pump hydromechanical effıciency, n—ratio of the
conditions of inlet pressure, motor shaft speed, and fluid
theoretical input torque of the pump to the actual torque input
temperature. Output torque, input flow, and case drain flow
of the pump.
rates are measured.
3.2.17 pump overall effıciency, n—ratio of the power trans-
4.4 The third section describes guidelines for field evalua-
ferred to the liquid, at its passage through the pump, to the
tions of hydraulic fluids. Baseline and test fluids are evaluated
mechanical input power.
in hydraulically powered machines. Energy consumption and
3.2.18 pump volumetric effıciency, n—ratio of the effective
duty cycle times are measured to compare the effects of fluids
output flow rate to the theoretical output flow rate.
on machine efficiency and productivity.
3.2.19 test oil, n—any oil subjected to evaluation in an
4.5 Differences between baseline and test fluid performance
established procedure.
are statistically evaluated.
3.2.19.1 Discussion—For purposes of this practice, the test
oil may be a hydraulic fluid of any suitable composition.
5. Significance and Use
3.3 Definitions of Terms Specific to This Standard: 5.1 The primary function of a hydraulic fluid is to transmit
3.3.1 design of experiment, DOE, n—statistical arrangement power. This practice provides uniform guidelines for compar-
ing fluids in terms of their power-transmitting abilities as
in which an experimental program is to be conducted and the
selection of the levels (versions) of one or more factors or reflected in their effect on hydraulic system or component
efficiency and productivity.
factor combinations to be included in the experiment.
3.3.2 duty cycle, n—time interval devoted to starting, 5.2 Practical advantages of enhanced hydraulic system ef-
running, stopping, and idling when a device is in use and the ficiency may include increased productivity (faster machine
time spent operating at different levels of speed, displacement cycle time), reduced power consumption (electricity or fuel),
and reduced environmental impact (lower emissions).
volume, torque, and pressure.
3.3.3 power factor, n—in AC electrical circuits, the ratio of 5.3 Differences in fluid performance may be relatively
actual electric power dissipated by the circuit to the product of small. Consequently, it is essential that the necessary experi-
the root mean square values of current and voltage; in DC mental controls are implemented to ensure consistency in
electrical circuits, it is the energy consumed (watts) versus the operating conditions and duty cycle when comparing the
product of input voltage (volts) times input current (amps). energy efficiency of different hydraulic fluid formulations.
D7721 − 22
5.4 This practice implies no evaluation of hydraulic fluid 6.1.4 Internal leakage flow loss measurements shall be used
quality other than its effect on hydraulic system efficiency. to compare the effects of fluids on pump performance if the
displacement is not fixed or the pump does not incorporate a
6. Procedure swashplate position sensor.
6.1.5 InstallthepumpinahydrauliccircuitasshowninFig.
6.1 Procedure for Laboratory Evaluation of Fluids in Posi-
1.
tive Displacement Pumps:
6.1.6 Sensors and Instrumentation—Precision instrumenta-
6.1.1 General Description—Hydraulic pump tests shall be
tion is necessary for determining the effect of hydraulic fluids
conducted on a hydraulic dynamometer via a modified ISO
on pump performance. Table 1 lists the systematic measuring
4409 method. ISO 4409 specifies a procedure for determining
instrument error limits for hydraulic fluid testing during
the performance and efficiency of hydraulic fluid power posi-
calibration. Sensors that comply with ClassArequirements are
tive displacement pumps, motors, and integral transmissions
recommended.
under steady-state conditions. It includes hydraulic circuit
6.1.7 Calibration—The calibration of all instruments shall
schematics, test procedures, and permissible systematic error
be verified. Pressure transducers in particular are susceptible to
limits. The purpose of the following procedure is to produce a
damage as a result of hydraulic pressure spikes.
statistical basis for comparing the performance of fluids in
terms of pump efficiency and/or internal leakage flow losses. 6.1.8 Flow Meter Selection—Positive displacement gear
type flow meters are recommended for dynamometer testing.
Modifications are required to the ISO 4409 method because
fluid performance, rather than pump performance, is to be In vehicle testing, it may be necessary to use another type of
flow meter to avoid excessive pressure losses that affect
evaluated.
6.1.2 Pump Selection—A positive displacement piston machine performance and efficiency.
pump that is employed in construction engineering, material 6.1.9 Baseline Oil—The baseline fluid shall be selected by
handling, or other off-highway vehicle applications shall be agreement of the responsible parties.
selected for testing. Load-sensing variable displacement axial
6.1.10 Pump Run-in—New pumps shall be run-in for 24 h
piston pumps are widely used in these applications and have
with the baseline fluid following the test sequence outlined in
been found to be suitable for hydraulic fluid efficiency testing.
Table 2.After the initial 3 h warm up (stages 1 – 5), run-in the
Use of other pump designs is permitted.
component for 20 h at rated pressure and speed (stage 6).Total
time for run-in shall be 24 h, including the 1 h cool down cycle
NOTE 1—A calculation of the theoretical flow rate is required to
(stage 7).Any mechanical issues arising during run-in shall be
determine the volumetric efficiency of a pump as shown in Eq X2.3. The
theoretical flow rate is determined from the mathematical product of the
fixed as necessary, with the run-in continuing where left off.
pump rotational speed (r/min) and derived displacement (Vi).
6.1.11 Fluid Flushing—A triple flush method shall be em-
6.1.3 Pump Derived Displacement—The derived displace- ployed to reduce carry over between fluids. Flush and drain the
ment of the pump shall be determined in accordance with ISO system three times. Change the oil filter. Fill the system and
8426. perform fluid Run-in.
FIG. 1 Circuit Schematic for Evaluating the Effect of Fluid on Pump Performance
D7721 − 22
TABLE 1 Systematic Measurement Error Limits as Determined During Calibration
Parameter Permissible Systematic Measuring Instrument Errors for Each Class of Measurement Accuracy
AB C
Rotational Frequency (%) ±0.5 ±1.0 ±2.0
Flow Rate (%) ±0.5 ±1.0 ±2.5
Torque (%) ±0.5 ±1.0 ±2.0
Pressure, wherep<0.15MPa gauge ±0.001 ±0.003 ±0.005
(MPa)
Pressure, where p$ 0.15 MPa (%) ±0.25 ±0.5 ±1.0
Test Fluid Temperature (°C) ±1.0 ±2.0 ±4.0
TABLE 2 24 h Run-in Sequence for New Hydraulic Pumps
Stage Time, h Mode Speed, % of rated Pressure, % of Displacement, % of Pump Inlet Temp,
max rated max rated max °C
1 0.5 Warm up 50 25 100 Ambient
2 0.5 Warm up 50 50 100 50 nominal
3 0.5 Warm up 75 50 100 50 nominal
4 0.5 Warm up 75 75 100 80 nominal
5 1.0 Warm up 100 75 100 80 nominal
6 20.0 Run-in 100 100 100 80 ± 1
7 1.0 Cool down 75 25 100 Ambient
6.1.12 Fluid Run-in—New baseline and candidate fluids shown in Table 3. Each of the twelve test points shall be
shall be run-in 500-turns of the reservoir at 50 °C and maxi- evaluated during a single run. A minimum of five runs of data
mum system pressure. shall be collected. The testing stage sequences may be altered
to help with temperature control.
NOTE 2—Fluid Run-in is performed to stabilize viscosity and tribologi-
6.1.16 Test Validation—Verify that inputs (Table 3) comply
cal surface conditions. Shearing of the fluid is more severe at 50 °C than
80 °C, hence fluid run-in is performed at the lower of these two with the limits provided in Table 1.
temperatures (50 °C).
6.1.17 Test Measurements—Record the following:
6.1.13 Calculation of the Run-in Time—The minimum
6.1.17.1 Input torque,
run-in duration shall be calculated as shown in Eq 1:
6.1.17.2 Input shaft speed,
6.1.17.3 Inlet temperature,
θ 5 ~q * 500!⁄~Vi ~n!*60! (1)
r
6.1.17.4 Inlet pressure,
where:
6.1.17.5 Outlet pressure,
θ = minimum fluid run-in duration in hours,
6.1.17.6 Outlet flow rate, and
q = volume of oil in the reservoir in liters,
r
6.1.17.7 Pumpcase,pressurecompensator,andmotordrain-
Vi = pump displacement in liters per revolution, and
age flow rates.
n = rotational frequency of the pump in r/min.
6.1.18 Evaluate the results as described in 7.1.
6.1.14 Pump Test Sequence—Each evaluation shall consist
6.2 Procedure for Laboratory Evaluation of Fluids in Posi-
of two segments: an initial fluid baseline and a candidate fluid
tive Displacement Motors:
evaluation.
6.1.15 Pump Test Conditions—The high-pressure pump 6.2.1 General Description—Hydraulic motor tests shall be
testingshallconsistofoperatingavariabledisplacementpiston conducted on a hydraulic dynamometer via a modified ISO
pump at maximum pressure and 80 °C under the conditions 4392-1 method. This part of ISO 4392 describes a method of
TABLE 3 Pump Test Parameters
Stage Time Mode Pump speed, % of Pressure, % of max Displacement, % of Pump Inlet Temp, °C
max max
0.1 h Warm up 40 – 50 20 – 30 100 nominal Ambient
0.1 h Warm up 50 – 60 50 – 60 100 nominal 50 nominal
0.3 h Warm up 60 – 70 70 – 80 100 nominal 80 nominal
0.5 h Warm up 100 100 100 nominal 80 nominal
1 $5 s Testing 100 100 100 80
2 $5 s Testing 100 100 80 80
3 $5 s Testing 100 100 60 80
4 $5 s Testing 100 90 100 80
5 $5 s Testing 100 90 80 80
6 $5 s Testing 100 90 60 80
7 $5 s Testing 90 100 100 80
8 $5 s Testing 90 100 80 80
9 $5 s Testing 90 100 60 80
10 $5 s Testing 90 90 100 80
11 $5s Testing 90908080
12 $5s Testing 90906080
D7721 − 22
determining the low-speed characteristics of positive displace- 6.2.8 Fluid Flushing—A triple flush method shall be em-
ment rotary fluid power motors, of either fixed or variable ployed to reduce carry over between fluids. Flush and drain the
displacement types. The method involves testing at constant system three times. Change the oil filter. Fill the system and
low-speed and high-pressure conditions. The purpose of the perform fluid run-in.
following procedure is to produce a statistical basis for
6.2.9 Fluid Run-in—Newbaselineandcandidatefluidsshall
comparing the performance of fluids in terms of hydraulic be run-in 500-turns of the reservoir at 50 °C and maximum
motor efficiency and/or torque losses. Modifications are re-
system pressure.
quired to the ISO 4392 method because fluid performance,
6.2.10 Calculation of the Run-in Time—The minimum
rather than motor performance, is to be evaluated.
run-in duration shall be calculated as shown in Eq 1.
6.2.2 Motor Selection—A positive displacement piston mo-
6.2.11 Motor Test Sequence—Each evaluation shall consist
tor that is employed in construction engineering, material
of two segments: an initial fluid baseline and a candidate fluid
handling, or other off-highway vehicle applications shall be
evaluation.
selected for testing.APoclain MSE02 Radial Piston Motor and
6.2.12 Motor Test Conditions—The low-speed high-torque
a Danfoss Series 90Axial Piston Motor have been found to be
motor test shall be conducted under the conditions shown in
suitable. Use of other motor designs is permitted.
Table 5. Each of the seven test points shall be evaluated during
a single run.Aminimum of five runs of data shall be collected.
NOTE3—Acalculationofthetheoreticaltorqueisrequiredtodetermine
the hydromechanical efficiency of a motor as shown in Eq X2.5. The testing stage sequences may be altered to help with
Theoretical torque is determined from the mathematical product of the
temperature control.
motor differential pressure and derived displacement (Vi).
6.2.13 Test Validation—Verify that inputs (Table 5) comply
6.2.3 The derived displacement of the motor shall be
with the limits provided in Table 1.
determined in accordance with ISO 8426.
6.2.14 Data Collection—Collect 15 s of data at each test
6.2.4 InstallthepumpinahydrauliccircuitasshowninFig.
point under steady-state conditions.
2.
NOTE 4—The motor rotates one-quarter revolution in 15 s during
6.2.5 See 6.1.6 – 6.1.8 for sensor, calibration, and flow rate
1 r⁄min testing.Ashorter sample duration my lead to excessive variability
requirements.
in the test results.
6.2.6 Baseline Oil—The baseline fluid shall be selected by
6.2.15 Test Measurements—Record the following motor
agreement of the responsible parties.
input and output parameters:
6.2.7 New Motor Run-in—New motors shall be run-in
6.2.15.1 Input flow rate,
according to manufacturer recommendations with the baseline
6.2.15.2 Inlet temperature,
fluid.Performingarun-insequenceisnecessarytostabilizethe
6.2.15.3 Inlet pressure,
performance of the motor in low-speed testing. If run-in
6.2.15.4 Outlet pressure,
procedure is not available from the manufacturer, use the
run-in sequence listed in Table 4. 6.2.15.5 Output torque,
FIG. 2 Circuit Schematic for Evaluating the Effect of Fluid on Motor Performance
D7721 − 22
TABLE 4 24 h Run-in Sequence for New Hydraulic Motors
Stage Time, h Mode Speed, % of rated max Pressure, % of rated Motor Inlet Temp, °C
max
1 1.0 Warm up 25 % 25 % 50 nominal
2 1.0 Run-in 50 % 50 % 50 nominal
3 1.0 Run-in 75 % 75 % 50 nominal
4 4.0 Run-in 100 % 100 % 80 nominal
5 4.0 Run-in 75 % 100 % 80 nominal
6 4.0 Run-in 50 % 100 % 80 nominal
7 4.0 Run-in 10 % 100 % 80 nominal
8 4.0 Run-in 5 % 100 % 80 nominal
9 1.0 Cool down 75 % 25 % Ambient
TABLE 5 Motor Test Parameters
...

This document is not an ASTM standard and is intended only to provide the user of an ASTM standard an indication of what changes have been made to the previous version. Because
it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D7721 − 17 D7721 − 22
Standard Practice for
Determining the Effect of Fluid Selection on Hydraulic
System or Component Efficiency
This standard is issued under the fixed designation D7721; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
1. Scope*
1.1 This practice covers all types and grades of hydraulic fluids.
1.2 This practice is applicable to both laboratory and field evaluations.
1.3 This practice provides guidelines for conducting hydraulic fluid evaluations. It does not prescribe a specific efficiency test
methodology.
1.4 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.5 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety safety, health, and healthenvironmental practices and determine the
applicability of regulatory limitations prior to use.
1.6 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
D4174 Practice for Cleaning, Flushing, and Purification of Petroleum Fluid Hydraulic Systems
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
2.2 ISO Standards:
ISO 4391 Hydraulic fluid power—Pumps, motors and integral transmissions—Parameter definitions and letter symbols
ISO 43924392–1 Hydraulic fluid power—Determination of characteristics of motorsmotors—Part 1: At constant low speed and
constant pressure
ISO 4409 Hydraulic fluid power—Positive displacement pumps—Methods power—Positive-displacement pumps, motors and
integral transmissions—Methods of testing and presenting basic steady state performance
ISO 5598 Fluid power systems & components—Vocabulary
This practice is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.N0 on Hydraulic Fluids.
Current edition approved May 1, 2017Sept. 1, 2022. Published June 2017October 2022. Originally approved in 2011. Last previous edition approved in 20112017 as
D7721 – 11.D7721 – 17. DOI:10.1520DOI:10.1520/D7721-22.⁄D7721-17.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at [e-mail]. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
Available from International Organization for Standardization (ISO), ISO Central Secretariat, BIBC II, Chemin de Blandonnet 8, CP 401, 1214 Vernier, Geneva,
Switzerland, http://www.iso.org.
*A Summary of Changes section appears at the end of this standard
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ISO 8426 Hydraulic fluid power—Positive displacement pumps and motors—Determination of derived capacity
2.3 Other Standards:
VDI 2198 Type Sheets for Industrial Trucks
3. Terminology
3.1 For additional definitions related to petroleum products and lubricants, see Terminology D4175. For additional definitions
related to fluid power systems and components, see ISO 5598.
3.2 Definitions:
3.2.1 baseline oil, n—oil of known performance characteristics used as a basis for comparison.
3.2.1.1 Discussion—
For purposes of this practice, the baseline oil may be a hydraulic fluid of any suitable composition.
3.2.2 component, n—of a hydraulic system, an individual unit, excluding piping, comprising one or more parts designed to be a
functional part of a fluid power system, for example, cylinder, motor, valve, or filter.
3.2.3 critical parts, n—those components used in the test that are known to affect test severity.
3.2.4 cycle time, n—the amount of time it takes for a machine to perform a repetitive segment of an operation, typically measured
as the time it takes a machine to return to the original position after completing a task.
3.2.4 effıciency, n—the ratio of actual work output of a component or machine to the theoretical work output calculated from the
measured input power.
3.2.5 energy consumption, n—the total energy content consumed during a test in kWh; determined from electric power meter
readings or calculated from the mass of fuel consumed and the lower heating value of the fuel.
3.2.6 energy effıciency, n—the work output divided by the energy input; this ratio may be expressed as a percentage.
3.2.7 fit for use, n—product, system, or service that is suitable for its intended use.
3.2.8 fuel rate, n—the rate at which fuel is consumed in L/h, normalized to the fuel density at 15 °C.
3.2.9 grade, n—designation given a material by a manufacturer so that it is always reproduced to the same specifications
established by standards organizations such as ASTM or ISO.
3.2.10 hydraulic fluid, n—liquid used in hydraulic systems for lubrication and transmission of power.
3.2.11 hydraulic system, n—fluid power system that is an arrangement of interconnected components which generates, transmits,
controls, and converts fluid power energy.
3.2.12 motor hydromechanical effıciency, n—ratio of the actual torque output of the motor to the theoretical torque output of the
motor.
3.2.13 motor overall effıciency, n—ratio of the mechanical output power to the power transferred from the liquid at its passage
through the motor.
3.2.14 motor volumetric effıciency, n—ratio of the theoretical inlet flow rate to the effective inlet flow rate.
3.2.15 outlier, n—result far enough in magnitude from other results to be considered not part of the set.
3.2.15.1 Discussion—
For purposes of this practice, classification of a result as an outlier shall be justified by statistical criteria in comparison with the
valid data points.
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3.2.16 pump hydromechanical effıciency, n—ratio of the theoretical input torque of the pump to the actual torque input of the
pump.
3.2.17 pump overall effıciency, n—ratio of the power transferred to the liquid, at its passage through the pump, to the mechanical
input power.
3.2.18 pump volumetric effıciency, n—ratio of the effective output flow rate to the theoretical output flow rate.
3.2.18 reference oil, n—oil of known performance characteristics used as a basis for comparison.
3.2.18.1 Discussion—
For purposes of this practice, the reference oil may be a hydraulic fluid of any suitable composition.
3.2.19 test oil, n—any oil subjected to evaluation in an established procedure.
3.2.19.1 Discussion—
For purposes of this practice, the test oil may be a hydraulic fluid of any suitable composition.
3.3 Definitions of Terms Specific to This Standard:
3.3.1 design of experiment, DOE, n—statistical arrangement in which an experimental program is to be conducted and the
selection of the levels (versions) of one or more factors or factor combinations to be included in the experiment.
3.3.2 duty cycle, n—time interval devoted to starting, running, stopping, and idling when a device is in use and the time spent
operating at different levels of speed, displacement volume, torque, and pressure.
3.3.3 effıciency improvement, n—a positive change in one or more parameters measured in a system or component that may be
defined as a reduction in fuel consumption, electrical power draw, or temperature, an increase in work produced or flow rate, or
any combination of these or other parameters.
3.3.3.1 Discussion—
This improvement is expressed as a percent increase that is obtained by dividing the test oil performance by the reference oil
performance and multiplying by 100 or, if appropriate, for example, temperature, then actual values can be reported.
3.3.3 power factor, n—in AC electrical circuits, the ratio of actual electric power dissipated by the circuit to the product of the
root mean square values of current and voltage.voltage; Inin DC electrical circuits, it is the energy consumed (watts) versus the
product of input voltage (volts) times input current (amps).
3.3.3.1 Discussion—
The power factor is the dimensionless ratio of energy used compared to the energy flowing through the wires.
3.3.4 system overall effıciency, n—in fluid power systems, the ratio of the output power of the system to the input power of the
system.
3.3.4.1 Discussion—
For integral transmissions and open-loop hydraulic circuits that drive a hydraulic motor, system overall efficiency is the ratio of
the output mechanical power at the hydraulic motor shaft to the input mechanical power at the pump shaft. Methods ISO 4391 and
ISO 4409 provide additional details for determining system efficiency in circuits with boost pumps.
4. Summary of Practice
4.1 The purpose of this practice is to define minimum technical requirements for conducting energy efficiency performance
comparisons of two or more hydraulic fluids in controlled laboratory or field evaluations. It is organized in three sections.
4.2 Controls and considerations based on both technical factors and practical experience are included.The first section describes
guidelines for a dynamometer evaluation of fluids in a high-pressure positive displacement pump. Baseline and test fluids are
evaluated under steady-state conditions of pump shaft speed, displacement, outlet pressure and fluid temperature. Input torque,
outlet flow and case drain flow rates are measured.
4.3 Requirements for test planning, testing conduct, and data analysis and reporting are described. The second section describes
D7721 − 22
guidelines for dynamometer evaluation of fluids in low-speed hydraulic motor testing. Baseline and test fluids are evaluated under
steady-state conditions of inlet pressure, motor shaft speed, and fluid temperature. Output torque, input flow, and case drain flow
rates are measured.
4.4 The third section describes guidelines for field evaluations of hydraulic fluids. Baseline and test fluids are evaluated in
hydraulically powered machines. Energy consumption and duty cycle times are measured to compare the effects of fluids on
machine efficiency and productivity.
4.5 Differences between baseline and test fluid performance are statistically evaluated.
5. Significance and Use
5.1 The purpose primary function of a hydraulic fluid is to cool and lubricate fluid power components, as well as transmit power.
This practice provides uniform guidelines for comparing fluids in terms of their power-transmitting abilities as reflected in their
effect on hydraulic system or component efficiency. Standard test methods ISO 4409 and ISO 4392 provide specifications for
evaluating the steady state performance of hydraulic pumps and motors but do not address technical requirements specific to
hydraulic fluid testing. efficiency and productivity.
5.2 Practical advantages of enhanced hydraulic system efficiency may include increased productivity (faster machine cycle time),
reduced power consumption (electricity or fuel), and reduced environmental impact (lower emissions).
5.3 Differences in fluid performance may be relatively small. Consequently, it is essential that the necessary experimental controls
are implemented to ensure consistency in operating conditions and duty cycle when comparing the energy efficiency of different
hydraulic fluid formulations.
5.3 Practical advantages of enhanced hydraulic system efficiency may include increased productivity (faster machine cycle time),
reduced power consumption (electricity or fuel), and reduced environmental impact (lowered emissions).
5.4 This practice implies no evaluation of hydraulic fluid quality other than its effect on hydraulic system efficiency.
6. Procedure
6.1 Protocol—A successful outcome is dependent on an evaluation of goals and methods at the outset along with an assessment
of potential sources of error. Such an evaluation requires a clearly defined test protocol that shall include: (1) statistical design of
experiment and analysis, (2) fluid order evaluation, (3) equipment selection, (4) analysis and mitigation of the test variables, and
(5) appropriate data collection methods. This ensures that both the reference and test oils are evaluated in exactly the same way,
thus ensuring a valid comparison is made.
6.1.1 Site Coordinator/Personnel Training—Because of the complexity of field trials, it is recommended that a designated site
coordinator be used to ensure any questions or concerns from site personnel are addressed and that test protocols are being
followed.
6.2 Statistical Design of Experiment (DOE)—A statistical DOE system shall be used to account for any test variability and ensure
any differences observed are significant to 95 % confidence limits.
6.1 Test Control—Procedure for Laboratory Evaluation of Fluids in Positive Displacement Pumps: There are a number of test
variables that can significantly influence efficiency measurements and shall be controlled.
6.3.1 Fluid Order—To account for the potential impact of machine drift/bias and lubricant carryover effects, it is highly
recommended that the efficiency of the reference fluid (A) be evaluated before and after each test fluid (B) evaluation. Alternating
the reference fluid and test fluid in an ABA or ABAB test sequence is satisfactory. When operator or test equipment variables may
have a significant impact on the test outcome, the operators and test equipment should also be alternated in a systematic manner.
6.1.1 Carryover Control—General Description—Hydraulic systems may retain a significant amount of residual fluid after they
have been drained. This residual fluid can create cross-contamination. The level of cross-contamination between test fluids shall
be kept to a minimum. In preparation for the evaluation of each fluid, the hydraulic system should be filled, flushed, and drained
D7721 − 22
of the test fluid at least once. Practice pump tests shall be conducted on a hydraulic dynamometer via a modified ISO 4409 method.
ISO 4409 specifies a procedure for determining the performance and efficiency of hydraulic fluid power positive displacement
pumps, motors, and integral transmissions under steady-state conditions. It includes hydraulic circuit schematics, test procedures,
and permissible systematic error limits. The purpose of the following procedure is D4174 provides specific recommendations to
facilitate this process. The cross-contamination level in the test fluid ideally should not exceed 10 % in field trials and 1 % in
laboratory evaluations. The amount of cross-contamination should be determined using an appropriate test method such as
elemental analysis, mass balance, infrared spectroscopy, or viscosity. This information to produce a statistical basis for comparing
the performance of fluids in terms of pump efficiency and/or internal leakage flow losses. Modifications are required to the ISO
4409 method because fluid performance, rather than pump performance, is to be included with the test results.evaluated.
6.3.2.1 Flushing Requirements for Surface Active Fluids (for Example, Friction Modified)—If any of the fluids under evaluation
contains surface-active friction-reducing materials (for example, friction modifiers), then extra precautions to minimize carryover
effects may be required. One of these precautions shall be to use a flush oil that is capable of removing such surface-active
additives.
6.1.2 Pump Selection—A positive displacement piston pump that is employed in construction engineering, material handling, or
other off-highway vehicle applications shall be selected for testing. Load-sensing variable displacement axial piston pumps are
widely used in these applications and have been found to be suitable for hydraulic fluid efficiency testing. Use of other pump
designs is permitted.
NOTE 1—A calculation of the theoretical flow rate is required to determine the volumetric efficiency of a pump as shown in Eq X2.3. The theoretical flow
rate is determined from the mathematical product of the pump rotational speed (r/min) and derived displacement (Vi).
6.1.3 Pump Derived Displacement—The derived displacement of the pump shall be determined in accordance with ISO 8426.
6.1.4 Internal leakage flow loss measurements shall be used to compare the effects of fluids on pump performance if the
displacement is not fixed or the pump does not incorporate a swashplate position sensor.
6.1.5 Install the pump in a hydraulic circuit as shown in Fig. 1.
6.1.6 Environmental Conditions (for Field Trials)—Sensors and Instrumentation—It is important to minimizePrecision instru-
mentation is necessary for determining the effect of differences in environmental conditions such as ambient temperature during
the conduct of a field test. This may require testing only during defined periods of the day over multiple days, or on multiple days
underhydraulic fluids on pump performance. Table 1 similar weather conditions. Record ambient temperature, atmospheric
FIG. 1 Circuit Schematic for Evaluating the Effect of Fluid on Pump Performance
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TABLE 1 Typical Systematic Measurement Error Limits as Determined During Calibration
Permissible Systematic Measuring
Instrument Errors for Each Class of
Parameter Measurement Accuracy
Parameter Permissible Systematic Measuring Instrument Errors for Each Class of Measurement Accuracy
A B C
Rotational Frequency (%) ±0.5 ±1 ±2
Rotational Frequency (%) ±0.5 ±1.0 ±2.0
Flow Rate (%) ±0.5 ±1.5 ±2.5
Flow Rate (%) ±0.5 ±1.0 ±2.5
Torque (%) ±0.5 ±1.0 ±2.0
Pressure, where p < 0.15 MPa (1.5 ±0.001 (±0.01) ±0.003 (±0.03) ±0.005 (±0.05)
bar) gauge
Pressure, where p < 0.15 MPa gauge ±0.001 ±0.003 ±0.005
(MPa)
Pressure, where p $ 0.15 MPa (1.5 ±0.05 (±0.5) ±0.15 (±1.5) ±0.25 (±2.5)
bar) gauge
Pressure, where p $ 0.15 MPa (%) ±0.25 ±0.5 ±1.0
Test Fluid Temperature (°C) ±0.5 ±1 ±2
Test Fluid Temperature (°C) ±1.0 ±2.0 ±4.0
pressure, and sea level at the beginning of each test sequence.lists the systematic measuring instrument error limits for hydraulic
fluid testing during calibration. Sensors that comply with Class A requirements are recommended.
6.3.3.1 Precipitation shall be avoided as much as possible during testing as it is difficult to account for variation in traction.
6.3.3.2 The recommended ambient temperature for machine testing is 15 °C to 30 °C.
6.1.7 Oil Temperature—Calibration—Oil temperature can have a significant influence on fluid performance and, therefore, should
be monitored to account for its influence on efficiency. Oil temperatures shall be measured as accurately as possible both in the
reservoir and at the pump inlet.The calibration of all instruments shall be verified. Pressure transducers in particular are susceptible
to damage as a result of hydraulic pressure spikes.
6.1.8 Oil Viscosity—Flow Meter Selection—Oil viscosity can have a significant influence on fluid efficiency and, therefore, should
be monitored from start to end of test to account for its influence on Positive displacement gear type flow meters are recommended
for dynamometer testing. In vehicle testing, it may be necessary to use another type of flow meter to avoid excessive pressure
losses that affect machine performance and efficiency.
6.1.9 Baseline Oil—The baseline fluid shall be selected by agreement of the responsible parties.
6.1.10 Oil Pressure—Pump Run-in—Oil pressure has a strong influence on hydraulic pump efficiency. It is important to ensure that
theNew pumps shall be run-in for 24 h with the baseline fluid following the test sequence outlined in Table 2equipment is operating
at comparable pressures during identical test operations between oils under test. If pressure changes as a result of factors other than
the work load (that is, leakage, pump wear) occur, the results will not be valid. After the initial 3 h warm up (stages 1 – 5), run-in
the component for 20 h at rated pressure and speed (stage 6). Total time for run-in shall be 24 h, including the 1 h cool down cycle
(stage 7). Any mechanical issues arising during run-in shall be fixed as necessary, with the run-in continuing where left off.
6.1.11 Fluid Flushing—A triple flush method shall be employed to reduce carry over between fluids. Flush and drain the system
three times. Change the oil filter. Fill the system and perform fluid Run-in.
6.1.12 Fluid Run-in—New baseline and candidate fluids shall be run-in 500-turns of the reservoir at 50 °C and maximum system
pressure.
TABLE 2 24 h Run-in Sequence for New Hydraulic Pumps
Stage Time, h Mode Speed, % of rated Pressure, % of Displacement, % of Pump Inlet Temp,
max rated max rated max °C
1 0.5 Warm up 50 25 100 Ambient
2 0.5 Warm up 50 50 100 50 nominal
3 0.5 Warm up 75 50 100 50 nominal
4 0.5 Warm up 75 75 100 80 nominal
5 1.0 Warm up 100 75 100 80 nominal
6 20.0 Run-in 100 100 100 80 ± 1
7 1.0 Cool down 75 25 100 Ambient
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NOTE 2—Fluid Run-in is performed to stabilize viscosity and tribological surface conditions. Shearing of the fluid is more severe at 50 °C than 80 °C,
hence fluid run-in is performed at the lower of these two temperatures (50 °C).
6.1.13 Calculation of the Run-in Time—The minimum run-in duration shall be calculated as shown in Eq 1:
θ 5 q * 500 ⁄ Vi n *60 (1)
~ !~ ~ ! !
r
where:
θ = minimum fluid run-in duration in hours,
q = volume of oil in the reservoir in liters,
r
Vi = pump displacement in liters per revolution, and
n = rotational frequency of the pump in r/min.
6.1.14 Operator Differences—Pump Test Sequence—It is usually preferable in mobile equipment to test reference and candidate
oils using the same operator. When not possible, procedures should be included to minimize the effects of any differences, for
example, account for differences in DOE—randomized testing and machine Each evaluation shall consist of two segments: an
initial fluid baseline and a candidate fluid evaluation.
6.3.8 Operating Conditions (Speed, Load, Duty Cycle)—The test procedure should define as specifically as practical such variables
as speed of operation, sequence of steps, and load. Also, the duty cycle shall be defined to hold as consistently as possible between
the test and reference oils. Where possible, standard duty cycles such as found in VDI 2198 should be employed.
6.3.9 Fuel Quality—Differences in fuel characteristics can contribute to changes in efficiencies during field testing. It is preferable
to conduct field evaluations using a single batch of fuel. When this is not possible, comparable fuel quality shall be included in
the test protocol.
6.1.15 Electric Power Quality—Pump Test Conditions—In systems drawing power from a common source such as plant
equipment, changes The high-pressure pump testing shall consist of operating a variable displacement piston pump at maximum
pressure and 80 °C under the conditions shown in Table 3load separate from the test equipment can affect electrical power quality.
In systems that may be affected, comparable power quality (for example, amps, watts, and power factor) shall be included in the
test protocol. Each of the twelve test points shall be evaluated during a single run. A minimum of five runs of data shall be
collected. The testing stage sequences may be altered to help with temperature control.
6.3.11 The recommended location for measuring electrical power consumption is between the variable frequency drive (or starter
in an across-the-line application) and the electric motor.
6.1.16 Fuel Measurement—Test Validation—Fuel gauges on commercialVerify that inputs (Table 3 hydraulic machines are
designed to indicate when fuel replenishment is necessary. Consequently, fuel gauge accuracy is insufficient for efficiency studies.
Fuel levels may be determined by using an auxiliary tank and weighing the amount of fuel) comply with the limits provided in
Table 1consumed or using fuel flow sensors.
TABLE 3 Pump Test Parameters
Stage Time Mode Pump speed, % of Pressure, % of max Displacement, % of Pump Inlet Temp, °C
max max
0.1 h Warm up 40 – 50 20 – 30 100 nominal Ambient
0.1 h Warm up 50 – 60 50 – 60 100 nominal 50 nominal
0.3 h Warm up 60 – 70 70 – 80 100 nominal 80 nominal
0.5 h Warm up 100 100 100 nominal 80 nominal
1 $5 s Testing 100 100 100 80
2 $5 s Testing 100 100 80 80
3 $5 s Testing 100 100 60 80
4 $5 s Testing 100 90 100 80
5 $5 s Testing 100 90 80 80
6 $5 s Testing 100 90 60 80
7 $5 s Testing 90 100 100 80
8 $5 s Testing 90 100 80 80
9 $5 s Testing 90 100 60 80
10 $5 s Testing 90 90 100 80
11 $5 s Testing 90 90 80 80
12 $5 s Testing 90 90 60 80
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6.3.12.1 In high pressure common rail diesel engines, a portion of the fuel flow is recirculated to cool the system. The fuel
consumption rate may be continuously measured using the system depicted in Fig. 1. This system measures the fuel sent to the
injection pump and isolates the unused fuel returned to the tank.
6.3.12.2 The energy content of fuel is affected by temperature due to the impact of thermal expansion on density. Fuel flow sensors
must be able to account for changes in fuel temperature and density as well as the volume of fuel consumed.
6.1.17 Test Measurements—Record the following:
6.1.17.1 Input torque,
6.1.17.2 Input shaft speed,
6.1.17.3 Inlet temperature,
6.1.17.4 Inlet pressure,
6.1.17.5 Outlet pressure,
6.1.17.6 Outlet flow rate, and
6.1.17.7 Pump case, pressure compensator, and motor drainage flow rates.
6.1.18 Evaluate the results as described in 7.1.
6.2 Subject Equipment Selection—Procedure for Laboratory Evaluation of Fluids in Positive Displacement Motors: The
equipment selected should be both fit for use (that is, representative of the type to which the testing will be applied) and having
all critical parts maintained in good working order.
6.2.1 General Description—Hydraulic motor tests shall be conducted on a hydraulic dynamometer via a modified ISO 4392-1
method. This part of ISO 4392 describes a method of determining the low-speed characteristics of positive displacement rotary
fluid power motors, of either fixed or variable displacement types. The method involves testing at constant low-speed and
high-pressure conditions. The purpose of the following procedure is to produce a statistical basis for comparing the performance
of fluids in terms of hydraulic motor efficiency and/or torque losses. Modifications are required to the ISO 4392 method because
fluid performance, rather than motor performance, is to be evaluated.
6.2.2 Motor Selection—A positive displacement piston motor that is employed in construction engineering, material handling, or
other off-highway vehicle applications shall be selected for testing. A Poclain MSE02 Radial Piston Motor and a Danfoss Series
90 Axial Piston Motor have been found to be suitable. Use of other motor designs is permitted.
NOTE 3—A calculation of the theoretical torque is required to determine the hydromechanical efficiency of a motor as shown in Eq X2.5. Theoretical
torque is determined from the mathematical product of the motor differential pressure and derived displacement (Vi).
6.2.3 The derived displacement of the motor shall be determined in accordance with ISO 8426.
6.2.4 Install the pump in a hydraulic circuit as shown in Fig. 2.
6.2.5 See 6.1.6 – 6.1.8 for sensor, calibration, and flow rate requirements.
6.2.6 Baseline Oil—The baseline fluid shall be selected by agreement of the responsible parties.
6.2.7 New Motor Run-in—New motors shall be run-in according to manufacturer recommendations with the baseline fluid.
Performing a run-in sequence is necessary to stabilize the performance of the motor in low-speed testing. If run-in procedure is
not available from the manufacturer, use the run-in sequence listed in Table 4.
6.2.8 Fluid Flushing—A triple flush method shall be employed to reduce carry over between fluids. Flush and drain the system
three times. Change the oil filter. Fill the system and perform fluid run-in.
D7721 − 22
FIG. 12 Schematic of Fuel Measurement SystemCircuit Schematic for Evaluating the Effect of Fluid on Motor Performance
TABLE 4 24 h Run-in Sequence for New Hydraulic Motors
Stage Time, h Mode Speed, % of rated max Pressure, % of rated Motor Inlet Temp, °C
max
1 1.0 Warm up 25 % 25 % 50 nominal
2 1.0 Run-in 50 % 50 % 50 nominal
3 1.0 Run-in 75 % 75 % 50 nominal
4 4.0 Run-in 100 % 100 % 80 nominal
5 4.0 Run-in 75 % 100 % 80 nominal
6 4.0 Run-in 50 % 100 % 80 nominal
7 4.0 Run-in 10 % 100 % 80 nominal
8 4.0 Run-in 5 % 100 % 80 nominal
9 1.0 Cool down 75 % 25 % Ambient
6.2.9 Fluid Run-in—New baseline and candidate fluids shall be run-in 500-turns of the reservoir at 50 °C and maximum system
pressure.
6.2.10 Calculation of the Run-in Time—The minimum run-in duration shall be calculated as shown in Eq 1.
6.2.11 Motor Test Sequence—Each evaluation shall consist of two segments: an initial flui
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