ISO 7986

• Abstract:

  This International Standard defines the test conditions and methods for assessing the performance of seals used in oil hydraulic reciprocating applications. The resulting specified characteristics may be published in manufacturer's literature to enable a direct comparison of seal performance. The seal under test may be a single seal or a combination seal package.

• Status: Not Published
• ICS: 23.100.60 - Filters, seals and contamination of fluids
• ICS: 83.140.50 - Seals
• Technical Committee: ISO/TC 131/SC 7 - Sealing devices
• Drafting Committee: ISO/TC 131/SC 7 - Sealing devices
• Current Stage: 6000 - International Standard under publication
• Start Date: 05-Sep-2026
• Completion Date: 19-Sep-2026

• Revises: ISO 7986:1997 - Hydraulic fluid power — Sealing devices — Standard test methods to assess the performance of seals used in oil hydraulic reciprocating applications
• Effective Date: 11-Nov-2023

Overview

ISO 7986: Hydraulic fluid power - Sealing devices - Standard test methods to assess the performance of rod seals used in oil hydraulic reciprocating applications provides a comprehensive framework for evaluating the performance of rod seals in hydraulic systems. Developed by the International Organization for Standardization (ISO), this standard specifies the test conditions and methodologies needed to ensure accurate, repeatable, and objective assessment of hydraulic rod seal performance. Reliable seal performance is essential for minimizing leakage, ensuring safety, and maximizing the lifetime of hydraulic equipment in various industrial sectors.

ISO 7986 is intended to provide consistent testing procedures so that manufacturers and users can directly compare technical data. The tests defined in this standard can be applied to single seals or to combination seal packages, thus supporting both the design and selection processes in hydraulic system engineering.

Key Topics

• Test Environment and Conditions: ISO 7986 specifies tight control over testing variables such as speed, pressure, stroke, temperature, and surface finish to enable valid comparability between results.
• Test Equipment and Installation: The standard details requirements for test rigs, including material specifications, installation tolerances, and rod and housing bore dimensions.
• Fluid Selection: Only synthetic hydrocarbon hydraulic oils, compliant with ISO 6743-4, must be used as test fluids, with strict filtration and reservoir specifications outlined.
• Measurement Techniques: Instructions for measuring key characteristics like seal leakage, friction, breakout force, surface roughness, and pressure using calibrated apparatus are included.
• Data Recording and Reporting: ISO 7986 promotes standardized data collection and reporting, ensuring data integrity and transparency in results.
• Calibration and Repeatability: The standard requires annual calibration of test and measurement equipment to national standards, and recommends conducting a minimum of six tests per seal type for robust data.

Applications

The standard is particularly valuable to:

• Hydraulic Component Manufacturers: Enables consistent performance testing and quality assurance of rod seals prior to market release.
• Equipment Designers: Assists in the preliminary selection of rod seals with documented comparative data, optimizing equipment reliability and efficiency.
• Maintenance and Reliability Teams: Provides a benchmarking tool for evaluating seal performance under specific operating parameters, supporting predictive maintenance strategies.
• Technical Procurement and Specification: Buyers and engineers can reference test results compliant with ISO 7986 for informed supplier selection and procurement decisions.
• Research and Development: Offers a uniform methodology for R&D teams conducting performance comparisons and iterative improvements in sealing technology.

By adopting the testing procedures in ISO 7986, organizations ensure clear, comparable, and reliable data that can be reflected in manufacturer literature and technical documentation. The standard’s rigorous controls over test variables minimize errors caused by installation or operational inconsistencies, resulting in trustworthy performance metrics.

Related Standards

To facilitate comprehensive testing and ensure alignment with industry best practices, ISO 7986 references several key standards:

• ISO 286-2: Geometrical product specifications - Standard tolerance classes for holes and shafts.
• ISO 683-2: Specifications for alloy steels for quenching and tempering, relevant to rod materials.
• ISO 6743-4: Classification of hydraulic fluids.
• ISO 10766: Housing dimensions for rectangular-section-cut bearing rings in hydraulic cylinders.
• ISO 1629: Nomenclature for rubber and latices used in seal materials.
• ISO 21920-2 and ISO 21920-3: Terminology and operators for surface texture parameters and measurements.
• ISO 5598: Vocabulary for fluid power systems and components.

Adherence to ISO 7986 alongside its referenced standards ensures a harmonized approach to hydraulic seal performance testing, supporting quality, interoperability, and global market acceptance.

---

Keywords: ISO 7986, hydraulic fluid power, rod seals, oil hydraulic reciprocating applications, sealing devices, standard test methods, seal performance, hydraulic systems, leak testing, seal friction, surface roughness, hydraulic seal testing

FINAL DRAFT
International
Standard
ISO/FDIS 7986
ISO/TC 131/SC 7
Hydraulic fluid power — Sealing
Secretariat: JISC
devices — Standard test methods to
Voting begins on:
assess the performance of rod seals
2026-07-10
used in oil hydraulic reciprocating
Voting terminates on:
applications
2026-09-04
Transmissions hydrauliques — Dispositifs d'étanchéité —
Méthodes d'essai normalisées d'évaluation des performances
des joints utilisés dans des applications alternatives à l'huile
hydraulique
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
Reference number
ISO/FDIS 7986:2026(en) © ISO 2026

FINAL DRAFT
ISO/FDIS 7986:2026(en)
International
Standard
ISO/FDIS 7986
ISO/TC 131/SC 7
Hydraulic fluid power — Sealing
Secretariat: JISC
devices — Standard test methods to
Voting begins on:
assess the performance of rod seals
used in oil hydraulic reciprocating
Voting terminates on:
applications
Transmissions hydrauliques — Dispositifs d'étanchéité —
Méthodes d'essai normalisées d'évaluation des performances
des joints utilisés dans des applications alternatives à l'huile
hydraulique
RECIPIENTS OF THIS DRAFT ARE INVITED TO SUBMIT,
WITH THEIR COMMENTS, NOTIFICATION OF ANY
RELEVANT PATENT RIGHTS OF WHICH THEY ARE AWARE
AND TO PROVIDE SUPPOR TING DOCUMENTATION.
© ISO 2026
IN ADDITION TO THEIR EVALUATION AS
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO­
LOGICAL, COMMERCIAL AND USER PURPOSES, DRAFT
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
INTERNATIONAL STANDARDS MAY ON OCCASION HAVE
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
TO BE CONSIDERED IN THE LIGHT OF THEIR POTENTIAL
or ISO’s member body in the country of the requester.
TO BECOME STAN DARDS TO WHICH REFERENCE MAY BE
MADE IN NATIONAL REGULATIONS.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland Reference number
ISO/FDIS 7986:2026(en) © ISO 2026

ii
ISO/FDIS 7986:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Letter symbols . 1
5 Test installation . 2
5.1 General .2
5.2 Mechanical details .7
5.2.1 Test rig rod .7
5.2.2 Test rig stroke .7
5.2.3 Test seal housing dimensions .7
5.2.4 Leakage collection and drain .8
6 Test parameters . 10
6.1 Test environment .10
6.2 Test fluid .11
6.3 Test fluid temperature .11
6.4 Test housing rod bearings .11
6.5 Test fluid pressure.11
6.6 Speed of linear actuator .11
6.7 Pressure and stroke cycle for dynamic test .11
7 Assembly of seals .13
8 Methods of measurement and measuring apparatus .13
8.1 Seal leakage . 13
8.2 Seal friction . 13
8.2.1 Load cell . 13
8.2.2 Determination of dynamic seal friction.14
8.2.3 Procedure for determining breakout friction .14
8.3 Pressure measurement . 15
8.3.1 Pressure gauge . 15
8.3.2 Pressure transducer . 15
8.4 Surface roughness . 15
8.5 Temperature measurement . 15
9 Calibration .16
10 Test procedure .16
10.1 Test programme .16
10.2 Repeat series .17
11 Presentation of results . 17
12 Identification statement (reference to this document) . 17
Annex A (normative) Seal and seal housing dimension data forms .18
Annex B (normative) Test results .20
Annex C (normative) Seal performance report . .21
Bibliography .24

iii
ISO/FDIS 7986:2026(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards are normally carried out
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO
collaborates closely with the International Electro-technical Commission (IEC) on all matters of electro-
technical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types
of ISO documents should be noted. This document is drafted in accordance with the editorial rules of the
ISO/IEC Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent
rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a)
patent(s) which may be required to implement this document. However, implementers are cautioned that
this may not represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the technical barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 131, Fluid power systems, Subcommittee SC 7,
Sealing devices.
This second edition cancels and replaces the first edition (ISO 7986:1997), which has been technically
revised.
The main changes are as follows:
— change the reference documents for the surface roughness to the latest edition;
— change key names to be clear;
— change the minimum pressure at return stroke 3 MPa to 5 % of test pressure;
— add the cross-sectional view of Figure 3.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.

iv
ISO/FDIS 7986:2026(en)
Introduction
0.1  General
It is widely recognised that the results from reciprocating seal testing can be unpredictable. The background
research carried out in support of the preparation of document has demonstrated that this unpredictability
is primarily a function of lack of control of critical variables affecting seal installation and operation.
In order to carry out direct comparisons of seal performance, it is necessary to control these variables to
closer limits than may be normal in industrial practice. The major variables that can affect seal performance,
often even within normal manufacturing tolerance ranges, are listed in Clause 3.
0.2  Purpose
The purpose of the test is to provide comparative data on individual reciprocating rod seal designs and to
provide a basis for the preliminary selection of seals based upon their relative performance. To achieve this,
it is necessary to carry out the tests under strictly defined operating conditions. This document, therefore,
defines standard values of speed, pressure, temperature and surface finish. The resulting specified
characteristics are applicable to be published in manufacturer’s literature to enable a direct comparison of
seal performance.
The seal test is applicable to a single seal or a combination seal package.
To make the test results as useful as possible, a range of operating conditions has been provided so that the
most appropriate conditions can be selected as a basis for comparison for initial seal selection.
The pressures are standard working pressures, selected from ISO 2944:
— 6,3 MPa (63 bar);
— 16 MPa (160 bar);
— 31,5 MPa (315 bar).
The speeds have been selected to include slow speed (where stick-slip and high wear may be issues), medium
speed for general purpose hydraulics and a representative high speed.
The constraints on installation and operation in this procedure have been proved by research, primarily
carried out at BHR Group in the United Kingdom, under sponsorship from European companies and
1)
international round robin seal tests to be necessary to achieve repeatable results . Any departure from the
standard operating condition and installation criteria cannot be considered a standard test.
0.3  Factors affecting seal performance
a) Installation:
— sealing system, i.e. design of bearing(s), seal(s) and leakage collection seal;
— installation tolerances including seal groove, rod and bearings, extrusion gap;
— rod material and hardness;
— surface finish of the rod, variations of surface finish outside the range of Ra 0,08 µm to Ra 0,15 µm, or
greater than Rz 1,2 µm or greater than Rt 1,5 µm, can significantly affect seal performance. Different seal
materials also have significantly varying requirements for the optimum surface finish;
1) This research report is reported by the following.
—  Performance Variation in Reciprocating Rubber Seals', R.K.Flitney and B.S.
Nau, Lubrication Engineering, VR44, 12, 993-1000, December 1988.
—  Factors affecting Reciprocating Seal Performance', R.K.Flitney, 10th
International Conference on Fluid Power, BHR Group, April 1993.

v
ISO/FDIS 7986:2026(en)
— surface finish of the groove surfaces must be less than Ra 0,8 µm, or Rz 3,2 µm, to avoid static leakage
and wear of the seal during pressure cycles;
— bearing material including its effects on rod texture and boundary layer;
— assembly cleanliness;
b) Operation:
— fluid, i.e. viscosity, lubricity, compatibility with seal material including additives and contamination
level;
— pressure including pressure cycle;
— speed, especially speed cycle;
— speed/pressure cycle, i.e. stop-start conditions;
— stroke, especially short strokes (2 × the seal contact widths or less) which prevent formation of a lubricant
film;
— temperature, i.e. its effect on viscosity and seal material properties;
— external environment.
It is necessary to consider all the above factors and their potential effect on seal performance when
comparing potential seal performance in an actual application to results obtained from the standard test

vi
FINAL DRAFT International Standard ISO/FDIS 7986:2026(en)
Hydraulic fluid power — Sealing devices — Standard test
methods to assess the performance of rod seals used in oil
hydraulic reciprocating applications
1 Scope
This document defines the test conditions and methods for assessing the performance of seals used in oil
hydraulic reciprocating applications.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 286-2, Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes — Part 2:
Tables of standard tolerance classes and limit deviations for holes and shafts
ISO 683-2, Heat-treatable steels, alloy steels and free-cutting steels — Part 2: Alloy steels for quenching and
tempering
ISO 1629, Rubber and latices — Nomenclature
ISO 21920-2, Geometrical product specifications (GPS) — Surface texture: Profile — Part 2: Terms, definitions
and surface texture parameters
ISO 21920-3, Geometrical product specifications (GPS) — Surface texture: Profile — Part 3: Specification
operators
ISO 5598, Fluid power systems and components — Vocabulary
ISO 6743-4, Lubricants, industrial oils and related products (class L) — Classification — Part 4: Family H
(Hydraulic systems)
ISO 10766, Hydraulic fluid power — Cylinders — Housing dimensions for rectangular-section-cut bearing rings
for pistons and rods
3 Terms and definitions
For the purpose of this document, the terms and definitions given in ISO 5598 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Letter symbols
Letter symbols used in this document are as follows:

ISO/FDIS 7986:2026(en)
Symbol
...

ISO/FDIS 7986:2026(en)
ISO /TC 131/SC 7
Secretariat: JISC
Date: 2026-05-13xx
Hydraulic fluid power — Sealing devices — Standard test methods to
assess the performance of rod seals used in oil hydraulic
reciprocating applications
Transmissions hydrauliques — Dispositifs d'étanchéité — Méthodes d'essai normalisées d'évaluation des
performances des joints utilisés dans des applications alternatives à l'huile hydraulique
FDIS stage
ISO/FDIS 7986:2026(en)
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication
may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying,
or posting on the internet or an intranet, without prior written permission. Permission can be requested from either ISO
at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8 • CP 401
CH-1214 Vernier, Geneva, Switzerland
Tel.+Phone: + 41 22 749 01 11
Fax. + 41 22 749 09 47
E-mail: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
ISO/FDIS 7986:2026(en)
Contents
Foreword . iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Letter symbols . 1
5 Test installation . 2
5.1 General . 2
5.2 Mechanical details . 7
6 Test parameters . 10
6.1 Test environment . 10
6.2 Test fluid . 11
6.3 Test fluid temperature . 11
6.4 Test housing rod bearings . 11
6.5 Test fluid pressure . 11
6.6 Speed of linear actuator . 11
6.7 Pressure and stroke cycle for dynamic test . 11
7 Assembly of seals . 13
8 Methods of measurement and measuring apparatus . 13
8.1 Seal leakage . 13
8.2 Seal friction . 13
8.3 Pressure measurement. 15
8.4 Surface roughness . 15
8.5 Temperature measurement . 16
9 Calibration . 16
10 Test procedure . 16
10.1 Test programme . 16
10.2 Repeat series . 17
11 Presentation of results . 17
12 Identification statement (reference to this document) . 17
Annex A (normative) Seal and seal housing dimension data forms . 18
Annex B (normative) Test results . 20
Annex C (normative) Seal performance report . 21
Bibliography . 24

iii
ISO/FDIS 7986:2026(en)
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards are normally carried out through
ISO technical committees. Each member body interested in a subject for which a technical committee has been
established has the right to be represented on that committee. International organizations, governmental and
non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the
International Electro-technical Commission (IEC) on all matters of electro-technical standardization.
The procedures used to develop this document and those intended for its further maintenance are described
in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of
ISO documents should be noted. This document is drafted in accordance with the editorial rules of the ISO/IEC
Directives, Part 2 (see www.iso.org/directives).
ISO draws attention to the possibility that the implementation of this document may involve the use of (a)
patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights
in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s)
which may be required to implement this document. However, implementers are cautioned that this may not
represent the latest information, which may be obtained from the patent database available at
www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation on the voluntary nature of standards, the meaning of ISO specific terms and expressions
related to conformity assessment, as well as information about ISO's adherence to the World Trade
Organization (WTO) principles in the technical barriers to Trade (TBT), see www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 131, Fluid power systems and components,
Subcommittee SC 7, Sealing devices.
This second edition cancels and replaces the first edition (ISO 7986:1997), which has been technically revised.
The main changes are as follows:
— — Changechange the reference documents for the surface roughness to the latest edition;
— — Changechange key names to be clear.;
— — Changechange the minimum pressure at return stroke 3 MPa to 5 % of test pressure.;
— — Addadd the cross-sectional view of Figure 3Figure 3.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
iv
ISO/FDIS 7986:2026(en)
Introduction
0.1 0.1  General
It is widely recognised that the results from reciprocating seal testing can be unpredictable. The background
research carried out in support of the preparation of document has demonstrated that this unpredictability is
primarily a function of lack of control of critical variables affecting seal installation and operation.
In order to carry out direct comparisons of seal performance, it is necessary to control these variables to closer
limits than may be normal in industrial practice. The major variables that can affect seal performance, often
even within normal manufacturing tolerance ranges, are listed in Clause 3clause 3 below.
0.2 0.2  Purpose
The purpose of the test is to provide comparative data on individual reciprocating rod seal designs and to
provide a basis for the preliminary selection of seals based upon their relative performance. To achieve this,
it is necessary to carry out the tests under strictly defined operating conditions. This document, therefore,
defines standard values of speed, pressure, temperature and surface finish. The resulting specified
characteristics are applicable to be published in manufacturer’s literature to enable a direct comparison of
seal performance.
The seal test is applicable to a single seal or a combination seal package.
To make the test results as useful as possible, a range of operating conditions has been provided so that the
most appropriate conditions can be selected as a basis for comparison for initial seal selection.
The pressures are standard working pressures, selected from ISO 2944:
— — 6,3 MPa (63 bar);
— — 16 MPa (160 bar);
— — 31,5 MPa (315 bar).
The speeds have been selected to include slow speed (where stick-slip and high wear may be issues), medium
speed for general purpose hydraulics and a representative high speed.
The constraints on installation and operation in this procedure have been proved by research, primarily
carried out at BHR Group in the United Kingdom, under sponsorship from European companies and
1 1)
international round robin seal tests to be necessary to achieve repeatable results . . Any departure from the
standard operating condition and installation criteria cannot be considered a standard test.

This research report is reported by the following.
—  Performance Variation in Reciprocating Rubber Seals', R.K.Flitney and B.S.
Nau, Lubrication Engineering, VR44, 12, 993-1000, December 1988.
—  Factors affecting Reciprocating Seal Performance', R.K.Flitney, 10th
International Conference on Fluid Power, BHR Group, April 1993.
1)
This research report is reported by the following.

—  Performance Variation in Reciprocating Rubber Seals', R.K.Flitney and B.S.

Nau, Lubrication Engineering, VR44, 12, 993-1000, December 1988.

—  Factors affecting Reciprocating Seal Performance', R.K.Flitney, 10th
v
ISO/FDIS 7986:2026(en)
0.3 0.3  Factors affecting seal performance
a) a) Installation:
— — sealing system, i.e. design of bearing(s), seal(s) and leakage collection seal;
— — installation tolerances including seal groove, rod and bearings, extrusion gap;
— — rod material and hardness;
— — surface finish of the rod, variations of surface finish outside the range of Ra 0,08 µm to Ra 0,15 µm, or
greater than Rz 1,2 µm or greater than Rt 1,5 µm, can significantly affect seal performance. Different seal
materials also have significantly varying requirements for the optimum surface finish;
— — surface finish of the groove surfaces must be less than Ra 0,8 µm, or Rz 3,2 µm, to avoid static leakage
and wear of the seal during pressure cycles;
— — bearing material including its effects on rod texture and boundary layer;
— — assembly cleanliness;
b) b) Operation:
— — fluid, i.e. viscosity, lubricity, compatibility with seal material including additives and contamination
level;
— — pressure including pressure cycle;
— — speed, especially speed cycle;
— — speed/pressure cycle, i.e. stop-start conditions;
— — stroke, especially short strokes (2 x × the seal contact widths or less) which prevent formation of a
lubricant film;
— — temperature, i.e. its effect on viscosity and seal material properties;
— — external environment.
It is necessary to consider all the above factors and their potential effect on seal performance when comparing
potential seal performance in an actual application to results obtained from the standard test

International Conference on Fluid Power, BHR Group, April 1993.

vi
ISO/FDIS 7986:2026(en)
Hydraulic fluid power — Sealing devices — Standard test methods to
assess the performance of rod seals used in oil hydraulic reciprocating
applications
1 Scope
This document defines the test conditions and methods for assessing the performance of seals used in oil
hydraulic reciprocating applications.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content constitutes
requirements of this document. For dated references, only the edition cited applies. For undated references,
the latest edition of the referenced document (including any amendments) applies.
ISO 286--2, Geometrical product specifications (GPS) — ISO code system for tolerances on linear sizes — Part 2:
Tables of standard tolerance classes and limit deviations for holes and shafts
ISO 683--2, Heat-treatable steels, alloy steels and free-cutting steels — Part 2: Alloy steels for quenching and
tempering
ISO 1629, Rubber and latices — Nomenclature
ISO 21920--2, Geometrical product specifications (GPS) — Surface texture: Profile — Part 2: Terms, definitions
and surface texture parameters
ISO 21920--3, Geometrical product specifications (GPS) — Surface texture: Profile — Part 3: Specification
operators
ISO 5598, Fluid power systems and components — Vocabulary
ISO 6743--4, Lubricants, industrial oils and related products (class L) — Classification — Part 4: Family H
(Hydraulic systems))
ISO 10766, Hydraulic fluid power — Cylinders — Housing dimensions for rectangular-section-cut bearing rings
for pistons and rods
3 Terms and definitions
For the purpose of this document, the terms and definitions given in ISO 5598 apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— — ISO Online browsing platform: available at https://www.iso.org/obp
— — IEC Electropedia: available at https://www.electropedia.org/
4 Letter symbols
Letter symbols used in this document are as follows:
ISO/FDIS 7986:2026(en)
Symbol Quantity Unit
d rod diameter mm
d relative level of intersection (see ISO 21920-2, ISO 21920-3)
c
dh seal heel inside diameter mm
dl seal lip inside diameter mm
D bore diameter (outside diameter of the seal housing) mm
E seal length mm
F friction force N
Fi the inherent total friction at mid-stroke of the test rig only (see 8.2.2.18.2.2.1)) N
the mean mid-stroke value of forward stroke and return stroke friction forces
F N
s
of each seal under test
the sum of the friction at mid-stroke of the test rig for two test seals on the
F N
T
forward and return strokes
l leakage ml
L seal housing length mm
preturn return pressure (return stroke) MPa
p test pressure (forward stroke) MPa
test
rod surface texture, arithmetical mean deviation (Ra) (see ISO 21920-2 and ISO µm
Ra
21920-3)
Rmr(p,dc) relative material ratio (Rmr) (see ISO 21920-2 and ISO 21920-3)
rod surface texture, total height of the surface profile (Rt) (see ISO 21920-2 and µm
Rt
ISO 21920-3)
rod surface texture, maximum height of the surface profile (Rz) (see µm
Rz
ISO 21920-2 and ISO 21920-3)
Sh radial seal section - heel mm
S radial seal section - lip mm
l
v test speed m/s
W leakage collection zone mm
5 Test installation
5.1 General
5.1.1 5.1.1 A typical test seal, a single acting rod seal, is shown in Figure 1Figure 1. The tests described
in this document shall be conducted using a suitable test rig possessing the features shown in
Figure 2Figure 2.
ISO/FDIS 7986:2026(en)
7986_ed2fig1.EPS
Figure 1 — Dimensions of typical test seal
Dimensions in millimetres
7986_ed2fig2.EPS
Key
1 linear actuator
2 leakage collection seal (see Figure 8Figure 8))
3 load cell
4 test rig piston rod
5 forward stroke
6 return stroke
7 leakage zone (see Figure 7Figure 7))
ISO/FDIS 7986:2026(en)
8 seal position A (see Figure 1Figure 1))
9 fluid outlet
10 leakage port A
11 static O-ring and back up ring
12 fluid inlet p
13 bearing rings
14 seal position B (see Figure 1Figure 1))
15 spacer
16 leakage port B
17 test seal housing (see Figure 6Figure 6))
18 optional position of actuator and load cell
19 steel cylinder
Figure 2 — Test arrangement – vertical section
Figure 3Figure 3 shows detail assembly
ISO/FDIS 7986:2026(en)
Dimensions in millimetres
7986_ed2fig3.EPS
Key
1 thermocouple
2 test oil – inlet bottom outlet top
3 pressure transducer
a)
Recess length (= seal housing length + spacer length)
−0,2
b)
Nominal seal housing bore diameter H7

Figure 3 — Plan detail of seal housing assembly
ISO/FDIS 7986:2026(en)
5.1.2 5.1.2 The bearing housing and housing spacer shall be designed and constructed as detailed in
Figure 4Figure 4 and Figure 5Figure 5. The bearing housing recommended to be
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