EN 26704:1991
(Main)Automatic steam traps - Classification (ISO 6704:1982)
Automatic steam traps - Classification (ISO 6704:1982)
Establishes a simple classification of the main types according to the mode of actuation of their obturation device and disregarding their details of conception and construction. Three categories of steam traps can be distinguished: mechanical traps, actuated by the level of condensate; thermostatic traps, actuated by the temperature of the condensate; thermodynamic traps, actuated by fluid dynamics.
Kondensatableiter - Klassifikation (ISO 6704:1982)
Purgeurs automatiques de vapeur d'eau - Classification (ISO 6704:1982)
La présente Norme internationale établit une classification simple des principaux types de purgeurs automatiques de vapeur d'eau, en fonction du mode de commande de leur dispositif d'obturation, quels que soient leurs détails de conception et de construction.
Avtomatični izločevalniki kondenzata - Klasifikacija (ISO 6704:1982)
General Information
- Status
- Published
- Publication Date
- 29-Sep-1991
- Technical Committee
- CEN/TC 69 - Industrial valves
- Drafting Committee
- CEN/TC 69 - Industrial valves
- Current Stage
- 9093 - Decision to confirm - Review Enquiry
- Start Date
- 18-Jun-2013
- Completion Date
- 18-Jun-2013
Relations
- Effective Date
- 28-Oct-2020
Overview
EN 26704:1991 (identical to ISO 6704:1982) provides a simple, functional classification of automatic steam traps based on the mode of actuation of their obturation device. The standard’s scope is limited to grouping the main types-without prescribing detailed design, construction or performance requirements-and it is intended to standardize terminology and classification across industry and standards bodies.
Key topics
- Purpose: establish a clear, technology‑neutral steam trap classification according to actuation method.
- Main categories:
- Mechanical traps - actuated by condensate level (e.g., closed float, open-top/bucket float, inverted float).
- Thermostatic traps - actuated by condensate temperature (e.g., vapour‑pressure traps, bimetallic/thermoelastic traps, liquid/solid expansion traps).
- Thermodynamic traps - actuated by fluid dynamics and pressure differences (e.g., obturator traps, impulse/piston traps, labyrinth orifice traps).
- Key concepts and terms: automatic steam trap, obturator, seat, pressure chamber, orifice, fluid flow direction, condensate behaviour.
- References to related ISO standards: ISO 6552 (terminology), ISO 6553 (marking), ISO 6554 (flanged trap dimensions).
- Diagrams: the standard uses schematic sketches to illustrate each trap type and its operating principle.
Applications
EN 26704:1991 is primarily a classification and reference document that supports practical use cases such as:
- Specifying trap type in steam system design and piping & instrumentation diagrams (P&IDs).
- Communicating requirements between engineers, manufacturers and procurement teams when selecting traps for steam distribution, process heating, HVAC and industrial steam systems.
- Training and documentation for maintenance and reliability teams to recognize trap families (mechanical, thermostatic, thermodynamic) and their typical operating behavior.
- Harmonizing national and international standards references used by standards committees, certification bodies and technical authors.
Who uses this standard
- Steam system designers and process engineers
- Valve and steam trap manufacturers and product managers
- Maintenance, reliability and facility managers
- Technical writers, specifiers and standards committees
Related standards
- ISO 6704:1982 - Automatic steam traps - Classification (original international text)
- ISO 6552, ISO 6553, ISO 6554 - referenced for terminology, marking and dimensional guidance
- National adoptions (example: SIST EN 26704:2000) reflect CEN/ISO transposition
This classification-focused standard is a practical reference for correctly identifying and specifying automatic steam traps by actuation principle, improving clarity across procurement, design and maintenance workflows in steam-using industries.
Frequently Asked Questions
EN 26704:1991 is a standard published by the European Committee for Standardization (CEN). Its full title is "Automatic steam traps - Classification (ISO 6704:1982)". This standard covers: Establishes a simple classification of the main types according to the mode of actuation of their obturation device and disregarding their details of conception and construction. Three categories of steam traps can be distinguished: mechanical traps, actuated by the level of condensate; thermostatic traps, actuated by the temperature of the condensate; thermodynamic traps, actuated by fluid dynamics.
Establishes a simple classification of the main types according to the mode of actuation of their obturation device and disregarding their details of conception and construction. Three categories of steam traps can be distinguished: mechanical traps, actuated by the level of condensate; thermostatic traps, actuated by the temperature of the condensate; thermodynamic traps, actuated by fluid dynamics.
EN 26704:1991 is classified under the following ICS (International Classification for Standards) categories: 23.040.99 - Other pipeline components. The ICS classification helps identify the subject area and facilitates finding related standards.
EN 26704:1991 has the following relationships with other standards: It is inter standard links to EN ISO 5117:2023. Understanding these relationships helps ensure you are using the most current and applicable version of the standard.
EN 26704:1991 is associated with the following European legislation: EU Directives/Regulations: 97/23/EC; Standardization Mandates: M/071. When a standard is cited in the Official Journal of the European Union, products manufactured in conformity with it benefit from a presumption of conformity with the essential requirements of the corresponding EU directive or regulation.
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Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Kondensatableiter - Klassifikation (ISO 6704:1982)Purgeurs automatiques de vapeur d'eau - Classification (ISO 6704:1982)Automatic steam traps - Classification (ISO 6704:1982)23.060.01Ventili na splošnoValves in generalICS:Ta slovenski standard je istoveten z:EN 26704:1991SIST EN 26704:2000en01-september-2000SIST EN 26704:2000SLOVENSKI
STANDARD
w - International Standard INTERNATIONAL ORGANIZATION FOR STANDARDIZATION.ME~KAYHAPO~HAR OWAHMSAUMR fl0 CTAWW’T~3Al&IWORGANISATION INTERNATIONALE DE NORMALISATION Automatic steam traps - Classification Purgeurs automatiques de vapeur d’eau - Classifica tion First edition - 1982-01-15 Corrected and reprinted - 1983-01-15 UDC 621.186.6 Ref. No. ISO 67044982 (E) Descriptors : industrial valves, traps, steam, classifications. Price based on 4 pages SIST EN 26704:2000
Foreword ISO (the International Organization for Standardization) is a worldwide federation of national Standards institutes (ISO member bodies). The work of developing Inter- national Standards is carried out through ISO technical committees. Every member body interested in a subject for which a technical committee has been set up 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. Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISO Council. International Standard ISO 6704 was developed by Technical Committee ISO/TC 153, Valves, and was circulated to the member bodies in February 1980. lt has been approved by the member bodies of the following countries : Australia Austria Belgium Brazil Canada China Czechoslovakia Denmark Finland France Germany, F. R. India Italy Korea, Rep. of Netherlands Norway No member body expressed disapproval of the document. 0 international Organkation for Standardkation, 1982 Poland Romania South Africa, Rep. of Sweden Switzerland United Kingdom USA USSR Printed in Switzerland SIST EN 26704:2000
INTERNATIONAL STANDARD ISO 6704-1982 (E) Automatic steam traps - Classification 1 Scope and field of application enclosure whilst remaining tight to live steam or, if necessary, allowing steam to flow at a predetermined rate. The purpose of this International Standard is to establish a simple classification of the main types of automatic steam traps according to the mode of actuation of their obturation device and disregarding their details of conception and construction. 4 Classification 2 References ISO 6552, Automatic steam traps - Terminology. ISO 6553, Automatic steam traps - Marking. ISO 6554, Flanged automatic steam traps - Face-to-face dimensions. 3 Definition For this International Standard, the following definition applies : automatic steam trap : Self-contained valve which automatically drains the co
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