ISO 6182-2:2025

International
Standard
ISO 6182-2
Fourth edition
Fire protection — Automatic
2025-07
sprinkler systems —
Part 2:
Requirements and test methods
for sprinkler system alarm valves,
check valves, water motor alarms,
retard devices and accelerators
Protection contre l'incendie — Systèmes d'extinction
automatiques du type sprinkler —
Partie 2: Exigences et méthodes d'essai des soupapes d'alarme
hydrauliques, des limiteurs de surpression et des dispositifs
d'alarme à moteur hydraulique
Reference number
© ISO 2025
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
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Production testing and quality control . 6
4.1 Responsibility .6
4.2 Production body strength test .6
4.3 Production operation test .6
4.4 Production leakage test .6
5 Requirements . 6
5.1 Overview .6
5.2 Nominal size .6
5.3 Connections .6
5.4 Rated working pressure .7
5.5 Body and cover .7
5.6 Strength (see 6.2) .7
5.7 Access for maintenance .7
5.8 Components (see 6.3, 6.4 and 6.12) .7
5.9 Leakage (see 6.5) .8
5.10 Non-metallic components (excluding gaskets, seals and other elastomeric parts) (see
6.5, 6.6, 6.7 and 6.11) . .9
5.11 Sealing assembly elements (see 6.8) .9
5.12 Clearances (see 6.9) .9
5.13 Hydraulic friction loss (see 6.10) . 13
5.14 Endurance (see 6.11) . 13
5.15 Operational performance (see 6.12) . 13
5.16 Equilibrium time (see 6.15) .14
5.17 Drains (see 6.4) . 15
5.18 Alarms (see 6.11) . 15
5.19 Retard devices (6.16) . 15
5.19.1 General . 15
5.19.2 Strength . 15
5.19.3 Strainer . 15
5.19.4 Support .16
5.19.5 Retard chamber drain .16
5.19.6 Components (see 6.6, 6.7, 6.12) .16
5.20 Height limitations for wet pilot lines (see 6.12) .16
5.21 Water motor alarms (see 6.17) .17
5.22 Water motor alarm connections (see 6.17) .17
5.23 Water motor alarm nozzles and strainers .17
5.24 Water motor alarm operation (see 6.17) .17
5.25 Water motor alarm bodies and covers .17
5.26 Water motor alarm audibility (see 6.17) .18
6 Tests . 19
6.1 Samples .19
6.2 Body strength (see 5.6) . 20
6.3 Spring and diaphragm test (see 5.8.5) . 20
6.4 Anti-reseating test of dry, preaction and deluge valves (see 5.8.6) . 20
6.5 Leakage and deformation tests (see 5.9).21
6.5.1 Body leakage test .21
6.5.2 Sealing assembly test .21
6.5.3 Wet and check valve leakage .21

iii
6.6 Warm water ageing test for non-metallic components (excluding gaskets and seals and
other elastomeric parts) (see 5.10, 5.19 and 5.21) .21
6.7 Air ageing test for non-metallic components (excluding gaskets and seals and other
elastomeric parts) (see 5.9, 5.18 and 5.20) . 22
6.8 Sealing element tests for valves (see 5.11) . 22
6.9 Salt mist corrosion test (see 5.12.2 and 5.12.7) . 23
6.9.1 Reagents . 23
6.9.2 Apparatus . 23
6.9.3 Procedure . 23
6.10 Hydraulic friction loss test for valves (see 5.13) . 23
6.11 Endurance test (see 5.14, 5.18) . 23
6.12 Operational tests (see 5.15, 5.20) .24
6.12.1 General .24
6.12.2 Installation . 25
6.12.3 Dry and preaction valve differential . 25
6.12.4 Preaction valve operation . 25
6.12.5 Preaction operational test in the dry mode (sprinkler operation with detection
fault) .27
6.13 Wet valve alarm and sensitivity test (see 5.15) .27
6.14 Wet and check valve ratio test (see 5.15.5) .27
6.15 Equilibrium time test (see 5.16) .27
6.16 Retard chamber (see 5.19) . 28
6.16.1 Strength . 28
6.16.2 Drainage . 28
6.17 Water motor alarm tests (see 5.21) . 28
6.17.1 Durability . 28
6.17.2 Audibility . 28
6.17.3 Strength of inlet connection . . 28
6.17.4 Water resistance . 28
7 Marking . .28
7.1 Body. 28
7.2 Cast markings . 28
7.3 Information to be marked . 29
8 Manufacturer’s installation instructions .29
8.1 Instructions . 29
8.2 Care and maintenance . 29

iv
Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is 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 Electrotechnical Commission (IEC) on all matters of electrotechnical 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 document should be noted. This document was 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 of 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 21, Equipment for fire protection and fire
fighting, Subcommittee SC 5, Fixed firefighting systems using water.
This fourth edition cancels and replaces the third edition (ISO 6182-2:2012), as well as ISO 6182-3:2012,
ISO 6182-4:2019, ISO 6182-5:2012, ISO 6182-6:2020 and ISO 6182-8:2019.
The main changes are as follows:
— Consolidation of ISO 6182-2:2012, ISO 6182-3:2012, ISO 6182-4:2019, ISO 6182-5:2012, ISO 6182-6:2020,
and ISO 6182-8:2019, into this document.
Inclusion of requirements for additional preaction valve variations.
A list of all parts in the ISO 6182 series can be found on the ISO website.
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.

v
International Standard ISO 6182-2:2025(en)
Fire protection — Automatic sprinkler systems —
Part 2:
Requirements and test methods for sprinkler system alarm
valves, check valves, water motor alarms, retard devices and
accelerators
1 Scope
This document specifies performance, requirements, methods of test and marking requirements for the
following equipment for use in automatic fire protection systems:
— wet alarm valves;
— retard devices;
— water motor alarms;
— dry pipe valves;
— accelerators;
— deluge valves;
— preaction valves;
— check valves.
Performance and test requirements for trim valves for alarm valves are not covered by this document.
The requirements for pressure reducing valves and fire pump relief valves are provided by ISO 6182-16 and
ISO 6182-17.
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 898-1, Mechanical properties of fasteners made of carbon steel and alloy steel — Part 1: Bolts, screws and
studs with specified property classes — Coarse thread and fine pitch thread
ISO 898-2, Mechanical properties of fasteners made of carbon steel and alloy steel — Part 2: Nuts with specified
property classes
3 Terms and definitions
For the purposes of this document, the following terms and definitions 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/
3.1
accelerator
device which hastens the operation of a dry pipe valve using mechanical means other than by reducing
installation pipework pressure
Note 1 to entry: For the purposes of this document, the term accelerator refers to an accelerator and any (internal or
external) antiflooding device.
Note 2 to entry: See also 3.3.
3.2
alarm device
mechanical or electrical device which sounds an alarm upon operation of the valve
3.3
antiflooding device
device intended to prohibit excessive water or other foreign matter from entering any relevant part or parts
of the accelerator where this can potentially prevent subsequent operation.
3.4
anti-reseating latch
component that prevents the sealing assembly from returning to its closed position after operation
3.5
automatic drain
device which is normally open and which automatically drains water from and vents the intermediate
chamber of a valve to the atmosphere when the valve is in the ready position, and which limits water flow
from the chamber after the valve has tripped
3.6
check valve
valve that permits flow into a pipe system and that prevents reverse flow
3.7
clapper
type of sealing assembly which includes rotational movement
Note 1 to entry: See also 3.28.
3.8
clapper-type valve
type of valve utilizing a clapper as the main sealing element which prevents flow from the system to the
supply side of the valve
3.9
compensator
external or internal device such as an auxiliary valve that minimizes false alarms caused by a small increase
of service pressure
3.10
corrosion-resistant material
bronze, brass or nickel-copper alloys such as UNS N04400, austenitic stainless steel, or equivalent metallic
or plastic material conforming with the requirements of this document
3.11
deluge system
automatic fire protection system using a deluge valve which is operated by an auxiliary means to admit
water into a system of open sprinklers or nozzles.

3.12
deluge valve
automatic water-supply control valve intended to be operated by an auxiliary means to admit water into a
system of open piping for a deluge system, or system of closed piping for a preaction system
Note 1 to entry: The auxiliary means of operating a deluge valve can be mechanical, electrical, hydraulic, pneumatic,
thermal, manual or a combination of these.
3.12.1
hydraulically operated deluge valve
deluge valve that is maintained in the set position by service hydraulic pressure acting against a diaphragm
or piston that holds the sealing assembly closed.
Note 1 to entry: A change in pressure against the diaphragm or piston allows the valve to open. The pressure is
changed by operation of a manual control, an electrical device such as solenoid valve, or hydraulically, thermally, or
pneumatically operated device.
3.12.2
pressure-loss operated deluge valve
valve in which the valve is released from the set position by reducing the pressure acting against an auxiliary
diaphragm or piston
3.12.3
supply pressure operated deluge valve
a valve that is maintained in the set position by a spring or other means and is hydraulically operated by the
application of service pressure to an auxiliary diaphragm or piston
3.13
differential
ratio of service pressure to system air pressure (expressed as gauge pressure) at the trip point
Note 1 to entry: See also 3.35.
3.14
differential type valve
type of valve in which air pressure in the system acts directly or indirectly or both on the sealing assembly
to maintain it in the closed position
Note 1 to entry: The air seat of the sealing assembly is of equal or larger diameter than the diameter of the water seat
of the sealing assembly, with the two separated by an intermediate chamber maintained at atmospheric pressure.
3.15
dry system
automatic fire sprinkler system in which the piping contains air or nitrogen under pressure, the release of
which allows water from a water supply to discharge through the system
3.16
dry pipe valve
valve that controls the flow of water into a dry pipe sprinkler system and incorporates a provision for
actuation of an alarm under specified conditions
3.17
holding chamber
chamber pressurized with system air pressure which actuates an accelerator upon a sufficient rate of loss of
system air pressure
3.18
intermediate chamber
part of a valve which separates the air and/or water sealing assembly seating surfaces and is at atmospheric
pressure when the valve is in the ready (set) condition

3.19
mechanical-type valve
type of valve in which the air pressure in the system acts on the sealing assembly and linking mechanism to
maintain it in the closed position
3.20
minimum opening pressure
minimum pressure at which water begins to pass through the valve
3.21
non-interlock preaction system
automatic fire sprinkler system in which water is admitted to the system upon either activation of a
supplemental detection system or loss of system pressure in combination with failure of the detection system
3.22
preaction system
automatic fire sprinkler system using a deluge valve that is operated by an auxiliary means to admit water
into a system of automatic sprinklers or other automatic spraying devices
3.23
preaction valve
preaction valve or valve combination which holds air in a closed sprinkler system and which is opened by
combination of sprinkler release or release system activation or both.
3.23.1
preaction valve Type A – non-interlocked
valve assembly which, under normal operating conditions, opens when either the release system or a
sprinkler operates
3.23.2
preaction valve Type B1 – Single-Interlocked with fail safe
valve assembly which, under normal operating conditions, opens only on the activation of a release system
Note 1 to entry: Type B1 valves operate as a dry system if the release system fails.
3.23.3
preaction valve Type B2 – Single-Interlocked without fail safe
valve assembly which, under normal operating conditions, opens only on the activation of a release system
Note 1 to entry: Type B2 valves can only be manually operated if the release system fail.
3.23.4
preaction valve Type C1 – Double-Interlocked with fail safe
valve assembly which, under normal operating conditions, opens when both the release system and a
sprinkler have operated
Note 1 to entry: Type C1 valves operate as a dry system if the release system fails.
3.23.5
preaction valve Type C2 – Double-Interlocked without fail safe
valve assembly which, under normal operating conditions, opens when both the release system and a
sprinkler have operated.
Note 1 to entry: Type C2 valves will not operate as a dry system and can only be manually operated if the release
system fails.
3.24
rated working pressure
maximum service pressure at which a valve or device is intended to operate

3.25
ready (set) condition
state of a valve with the sealing assembly in the closed or set position with service and system pressure applied
3.26
retard chamber
volumetric type of retard device designed to minimize false alarms caused by surges and fluctuations in
sprinkler system water supplies
3.27
retard device
pneumatic, hydraulic or electric timer designed to minimize false alarms caused by surges and fluctuations
in sprinkler system water supplies
3.28
sealing assembly
main movable sealing element (such as a clapper) of the valve which prevents the reverse flow of water
3.29
sealing assembly seat ring
main fixed sealing element of a valve which prevents the reverse flow of water
3.30
sensitivity
minimum rate of flow from a system outlet which will open the wet alarm valve, as indicated by satisfactory
operation of alarms
3.31
service pressure
static water pressure at the inlet to a valve when the valve is in the ready condition
3.32
system pressure
static water pressure at the main outlet of a valve when the valve is in the ready condition
3.33
system air pressure
static air pressure in the system piping when the valve is in the ready condition
3.34
trim
external equipment and pipework, excluding the main installation pipework, fitted to the valve
3.35
trip point
point at which a valve operates, admitting water into the system, measured in terms of the system air
pressure at a given service pressure
3.36
water motor alarm
hydraulically actuated device which provides a local audible alarm as a result of a flow through a valve
3.37
wet alarm valve
valve that permits flow of water into a wet sprinkler system, prevents the reverse flow of water and
incorporates a provision for actuation of an alarm under specified flow conditions.
3.38
wet pilot line
hydraulic detection and actuation piping system fitted with heat responsive devices, usually automatic
sprinklers, which, when subjected to heat from a fire, operate to release pressure from the actuation piping
system causing the automatic operation of a deluge valve

3.39
wet pipe system
automatic fire protection system in which the piping contains water and is connected to a water supply so
that water discharges upon operation of the sprinklers
4 Production testing and quality control
4.1 Responsibility
It shall be the responsibility of the manufacturer to implement and maintain a quality control programme
to ensure that production continuously meets the requirements of this document in the same manner as the
originally tested samples.
4.2 Production body strength test
Every manufactured valve set shall pass a hydrostatic body strength test for a period not less than 1 min at
twice the rated working pressure without leakage.
4.3 Production operation test
Following the body strength in 6.2, every manufactured valve or accelerator shall pass an operation test for
correct function.
4.4 Production leakage test
No manufactured valve shall leak when tested in accordance with 6.5.3 for a period of 1 min.
5 Requirements
5.1 Overview
Unless otherwise stated, the requirements of Clause 5 apply to all valves and devices within the scope of this
document.
5.2 Nominal size
The nominal size of wet, dry, deluge, check and preaction alarm valves and check valves shall be the nominal
diameter of the inlet and outlet connections, i.e. the pipe size for which the connections are intended.
Acceptable sizes shall be 25 mm, 32 mm, 40 mm, 50 mm, 65 mm, 80 mm, 100 mm, 125 mm, 150 mm, 200 mm,
250 mm, 300 mm, 350 mm, or 400 mm. The diameter of the waterway through any sealing assembly may be
less than the nominal size.
5.3 Connections
5.3.1 All connections shall be designed for use at the rated working pressure of the valve set.
5.3.2 The dimensions of all connections shall conform with the applicable requirements of relevant
International Standards.
NOTE If International Standards are not applicable, national standards can be permitted to be used.
5.3.3 Openings on wet, dry, deluge and preaction valves not smaller than 15 mm nominal diameter shall
be provided for an alarm line connection.
5.3.4 Dry, deluge and preaction valves shall be provided with means to prevent water columning.

5.3.5 Dry, deluge and preaction valves shall be provided with means to facilitate testing of alarms without
tripping the valve.
5.3.6 For differential-type dry or preaction valves, suitable means shall be provided to vent water from
the intermediate chamber and to prevent a partial vacuum between the upstream and downstream sealing
elements of the sealing assembly.
5.4 Rated working pressure
The rated working pressure shall be not less than 1,2 MPa (12 bar).
5.5 Body and cover
5.5.1 The body and cover shall be made of a material having corrosion resistance at least equivalent to
cast iron.
5.5.2 Cover fasteners shall be made of steel, stainless steel, titanium, or other materials with equivalent
physical and mechanical properties.
5.5.3 Non-metallic materials other than gaskets, diaphragms and seals or metals with a melting point less
than 650 °C shall not form part of the valve or accelerator body or cover.
5.5.4 It shall not be possible to assemble the valve with the cover plate in a position which either
improperly indicates flow direction or prevents proper operation of the valve or accelerator.
5.6 Strength (see 6.2)
5.6.1 An assembled valve or accelerator, with the sealing assembly blocked open (where applicable), shall
withstand, without rupture, an internal hydrostatic pressure of four times the rated working pressure for a
period of 5 min when tested as specified in 6.2.
5.6.2 If the test in accordance with 6.2 is not performed with standard production fasteners, the supplier
shall provide documentation showing that the calculated design load of any fastener, neglecting the force
required to compress the gasket, shall not exceed the minimum tensile strength specified in ISO 898-1 and
ISO 898-2 when the valve is pressurized to four times the rated working pressure. The area of the application
of pressure shall be calculated as follows:
a) If a full-face gasket is used, the area of application of pressure is that extending out to a line defined by
the inner edge of the bolts.
b) If an “O”-ring seal or ring gasket is used, the area of application of force is that extending out to the
centreline of the “O”-ring or gasket.
5.7 Access for maintenance
Means shall be provided to permit access to working parts and removal of the sealing assembly.
5.8 Components (see 6.3, 6.4 and 6.12)
5.8.1 Any component that is normally disassembled during servicing shall be designed so that it cannot
be reassembled improperly without providing an external visual indication when the valve is returned to
service.
5.8.2 With the exception of valve seats, all parts intended for field replacement shall be capable of being
disassembled and reassembled using tools normally employed by the trade.

5.8.3 Failure of the sealing assembly diaphragms or seals of wet, dry, deluge, preaction and check valves
shall not prevent the valve from opening.
5.8.4 Seat surfaces of sealing assemblies shall be constructed of a corrosion resistant material and have
sufficient width of surface contact to withstand ordinary wear and tear, rough usage, compression stresses
and damage due to pipe scale or foreign matter carried by the water.
5.8.5 Springs and diaphragms shall not fracture or rupture during the cyclic testing in accordance with 6.3.
5.8.6 For dry, deluge and preaction valves there shall be no sign, on visual examination, of damage to the
sealing assembly after testing for the operational requirements of 5.15 in accordance with 6.12 and 6.4.
5.8.7 For wet, dry, deluge, preaction and check valves when wide open, the sealing assembly shall bear
against a definite stop. The opening of the valve or reaction of the water shall not permanently twist, bend
or fracture valve parts.
5.8.8 Where rotation or sliding motion is required, the part or its bearing shall be made of a corrosion-
resistant material. Materials lacking corrosion resistance shall be fitted with bushings, inserts or other
parts made of corrosion-resistant materials at those points where freedom of movement is required.
5.8.9 The sealing assembly in wet and check valves shall close towards the seat when water flow ceases.
Springs shall be permitted to ensure full and proper seating.
5.8.10 A dry, preaction, or deluge valve shall be provided with means to prevent the valve from automatically
returning to the ready (set) condition and to permit draining of the pipework after the valve has tripped.
Manual or external means shall be provided to return the valve to the ready (set) condition.
5.9 Leakage (see 6.5)
5.9.1 There shall be no leakage, permanent distortion or rupture of a valve or accelerator when an internal
pressure of twice the rated working pressure is applied for 5 min with the sealing assembly open when
tested in accordance with 6.5.1.
5.9.2 For clapper-type valves there shall be no leakage past the sealing assembly, permanent distortion or
rupture at an internal pressure of twice the rated working pressure applied to the downstream side of the
sealing assembly for 5 min with the upstream end vented in accordance with 6.5.2.
For valves equipped with an intermediate chamber and alarm port, leakage into the intermediate chamber
or alarm port shall be considered as a leak and consequently a failure of the requirements of this test.
5.9.3 For non-clapper type valves there shall be no leakage past the sealing assembly, permanent
distortion or rupture at an internal pressure of twice the rated working pressure applied to the upstream
side of the sealing assembly of a valve in the ready position for 5 min with the downstream end vented in
accordance with 6.5.2.
For valves equipped with an intermediate chamber and alarm port, leakage into the intermediate chamber
or alarm port shall be considered as a leak and consequently a failure of the requirements of this test.
5.9.4 There shall be no leakage of an accelerator when a pneumatic pressure of 0,7 MPa (7 bar) is applied
for 1 min in accordance with 6.5.2.4.

5.9.5 For wet and check valves there shall be no leakage past the sealing assembly, permanent distortion
or rupture at an internal pressure of twice the rated working pressure applied to the downstream side of
the sealing assembly for 5 min with the upstream end vented in accordance with 6.5.3.
For valves equipped with an intermediate chamber and alarm port, leakage into the intermediate chamber
or alarm port shall be considered as a leak and consequently a failure of the requirements of this test.
5.10 Non-metallic components (excluding gaskets, seals and other elastomeric parts) (see
6.5, 6.6, 6.7 and 6.11)
Non-metallic parts that may affect proper valve or device function as defined in this standard shall
be subjected to the applicable ageing tests as described in 6.6 and 6.7 using separate sets of samples,
as applicable. After ageing, a valve or device shall meet the requirements of 5.9 and 5.15 when tested in
accordance with the applicable tests described in 6.5.1 and 6.11.
There shall be no cracking, warping, creep, or other signs of deterioration that can preclude proper operation
of the valve or device.
5.11 Sealing assembly elements (see 6.8)
A seal made of elastomeric or other resilient materials shall not adhere to the mating surface when tested in
accordance with 6.8. Where the same design of seat is used for more than one size of valve, or device it shall
be permitted to test only the size with the highest stress on the seating surface.
5.12 Clearances (see 6.9)
5.12.1 The requirements of 5.12.2 to 5.12.11 are applicable to hinged, clapper-type valves only.
5.12.2 The radial clearance between a hinged sealing assembly and the inside walls in every position except
wide open shall not be less than 12 mm for cast iron bodies and shall not be less than 6 mm if the body
and sealing assembly are of cast iron or steel with corrosion protective coatings tested in accordance with
6.9, non-ferrous material, stainless steel or materials having equivalent physical, mechanical and corrosion-
resistant properties. See Figure 1.
5.12.3 There shall be a diametrical clearance (see Figure 1) between the inner edges of the seat ring and
the metal parts of the sealing assembly when in the closed position (excluding any anti-reseating latch) as
follows:
a) for compression snap-type sealing assemblies of corrosion-resistant materials, the diametrical
clearance shall be not less than 0,7 mm;
b) for other types of sealing assemblies, the diametrical clearance shall be not less than 3 mm.
5.12.4 Any space in which the sealing assembly can trap debris beyond the seat shall be not less than
3 mm deep.
5.12.5 The diametrical clearance between hinge pins and their bearings shall be not less than 0,125 mm.
5.12.6 The total axial clearance between the clapper hinge and adjacent valve body bearing surfaces shall
be not less than 0,25 mm. See Figure 1.
5.12.7 Sealing assembly guide bushings or hinge-pin bearings shall project a sufficient axial distance to
maintain not less than 1,5 mm (bushing projection, see Figure 1 c or d) clearance between ferrous metal
parts. see Figure 1. Clearance less than 1,5 mm shall be permitted where adjacent parts are of bronze,
brass, Monel metal, austenitic stainless steel, titanium, or similar corrosion-resistant materials. When
corrosion resistance of steel parts is provided by a protective coating, the parts shall show no visible signs
...