ISO 19973-2:2015/Amd 1:2019

INTERNATIONAL ISO
STANDARD 19973-2
Second edition
2015-09-01
AMENDMENT 1
2019-02
Pneumatic fluid power — Assessment
of component reliability by testing —
Part 2:
Directional control valves
AMENDMENT 1
Transmissions pneumatiques — Évaluation par essais de la fiabilité
des composants —
Partie 2: Distributeurs
AMENDEMENT 1
Reference number
ISO 19973-2:2015/Amd.1:2019(E)
©
ISO 2019
ISO 19973-2:2015/Amd.1:2019(E)

© ISO 2019
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ii © ISO 2019 – All rights reserved

ISO 19973-2:2015/Amd.1:2019(E)

Foreword
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This document was prepared by Technical Committee ISO/TC 131, Fluid power systems.
A list of all parts in the ISO 19973 series can be found on the ISO website.
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ISO 19973-2:2015/Amd.1:2019(E)
Pneumatic fluid power — Assessment of component
reliability by testing —
Part 2:
Directional control valves
AMENDMENT 1
Clause 2 Normative references, Page 1
Add the following references to Clause 2.
ISO 12238, Pneumatic fluid power — Directional control valves — Measurement of shifting time
ISO 13849-1, Safety of machinery — Safety-related parts of control systems — Part 1: General
principles for design
ISO 13849-2, Safety of machinery — Safety-related parts of control systems — Part 2: Validation
Add the following new Annex B for the estimation of B values for valves used in functional safety
10D
applications.
ISO 19973-2:2015/Amd.1:2019(E)

Annex B
(normative)
Estimating B for valves used in functional safety applications
10D
B.1 Introduction
When a machine is built, a risk assessment must be conducted for evaluation of potential hazards
according to ISO 12100. This is also a requirement in the ISO 4413 and ISO 4414 standards for hydraulic
and pneumatic systems. ISO 13849 is a standard that describes a method for risk reduction on safety
related parts of control systems, in accordance with ISO 12100. Components in safety related parts
of control systems shall have sufficient reliability to perform their function when a hazard occurs,
otherwise the component is considered to have failed dangerously.
Reliability of a pneumatic component is typically characterized by its B , η and β values, obtained from
a Weibull plot using all defined failures from Clause 8. B values are obtained only from failures that
10D
are classified as dangerous. For pneumatic valves, shifting off-time failures are considered dangerous
failures whereas shifting on-time failures are not considered dangerous because, according to the
basic safety principle (“use of de-energization principle” of ISO 13849-2:2012, Table B.1), that is not the
action typically required for implementing a safety function. Leakage is a performance failure and not
considered a dangerous failure (unless it is so severe as to prevent a return shift). Minimum shifting
pressure is not considered a dangerous failure because it is typically much lower than the operating
pressure of a system. If these or additional failure types (based upon a specific application) lead to a
dangerous failure, these failure mechanisms shall be considered as well. Additional failure mechanisms
shall clearly be based on agreement between supplier and purchaser.
The method for estimating a B life in this Annex is based on using the termination life at the first
10D
termination failure in a sample of seven test units. The cumulative failure for that first of seven test
units is 9,4 % (from a Median Rank table). This is close to the 10 % level on which the B life is
10D
defined, and the first failure life is considered to be an acceptable estimate for the B . Thus, it is not
10D
necessary to continue the test after the first termination failure. If there is one suspension in the sample
of seven test units, before a first termination failure occurs, the cumulative failure is 11,4 % at the first
failure life. This is still considered to be an acceptable estimate of the B life.
10D
The ISO 13849 series of standards includes two other methods to estimate a B life:
10D
1) B = 2 × B if only B data is available,
10D 10 10
2) B = 20 million cycles as a default value if data is not available.
10D
These methods are applicable to a user of the ISO 13849 series of standards if no B values are
10D
available; whereas this Annex is for a supplier for testing to estimate a B value.
10D
B.2 Test equipment and test conditions
Set up the test equipment in accordance with Clause 5.
2 © ISO 2019 – All rights reserved

ISO 19973-2:2015/Amd.1:2019(E)

B.3 Measurement of immediate shifting off-time
B.3.1 General
Testing can be integrated with the procedures described in Clause 7 if all failure data is included in one
test program. But the special procedures in B.3.3 and B.3.4 for shifting time in the return-OFF function
(shifting off-time) shall be followed for valves intended to be used in safety applications.
B.3.2 Functional check
Functional checks shall be conducted according to 7.2.1.
B.3.3 Immediate shifting off-time
The shifting off-time for each valve shall be recorded every time that data is taken. Start from a shifted
position with all volumes attached (including pressure transducers). Apply a supply pressure of
≈6,3 bar (630 kPa) to the inlet port (and also to an external pilot port if so equipped). Conduct a shifting
off-time test (exhaust test) in accordance with ISO 12238, with the excepti
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