prEN ISO 6704

• Abstract:

  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.

• Status: Not Published
• Publication Date: 09-Jan-2028
• ICS: 23.060.01 - Valves in general
• Technical Committee: CEN/TC 69 - Industrial valves
• Drafting Committee: CEN/TC 69 - Industrial valves
• Current Stage: 4060 - Closure of enquiry - Enquiry
• Start Date: 07-Sep-2026
• Completion Date: 07-Sep-2026
• Ref Project: oSIST prEN ISO 6704:2026 - Automatic steam traps - Classification (ISO/DIS 6704:2026)

• Revises: EN 26704:1991 - Automatic steam traps - Classification (ISO 6704:1982)
• Effective Date: 05-Mar-2025

Overview

prEN ISO 6704:2026, Automatic Steam Traps - Classification provides an internationally recognized classification system for automatic steam traps based on the mode of actuation of their obturation devices. Developed by CEN and ISO/TC 153, this standard intentionally excludes detailed design and construction features, focusing solely on the operational principle behind each main steam trap type. By clarifying definitions and categories, prEN ISO 6704:2026 supports consistency in technical communication and specification across industries that utilize steam systems.

Automatic steam traps play a crucial role in energy efficiency, steam system reliability, and process safety by ensuring the efficient removal of condensate while preventing steam loss. The standard distinguishes three primary categories:

• Mechanical steam traps
• Thermostatic steam traps
• Thermodynamic steam traps

Key Topics

• Mechanical Steam Traps:
  Actuated by the level of condensate within the trap, these include variants such as closed float types (with or without a lever) and open top or inverted bucket designs.

• Thermostatic Steam Traps:
  Actuated by the temperature of the condensate. Types include vapour pressure traps, bimetallic or thermoelastic traps, and special forms using disc or cantilever elements.

• Thermodynamic Steam Traps:
  Operate based on fluid dynamics, opening and closing in response to pressure differences and flow patterns. Subtypes include disc traps, impulse traps, and orifice traps.

• Definitions and Terminology:
  Includes harmonized terms such as 'obturator' (the movable element within the valve controlling flow) for clarity in standardization and procurement.

Applications

prEN ISO 6704:2026 offers significant value across multiple application areas:

• Steam System Design and Maintenance:
  Enables designers, engineers, and maintenance teams to specify and select appropriate automatic steam trap types based on operating principles rather than manufacturer-specific designs, supporting interoperability and best-fit solutions.

• Energy Management and Efficiency:
  Correct steam trap classification assists in optimizing steam usage, decreasing energy loss, and minimizing maintenance costs, directly contributing to sustainable operation of boilers, heat exchangers, and process equipment.

• Industrial Sectors:
  Applicable in industries such as power generation, chemical processing, petrochemical, food and beverage, pharmaceuticals, and HVAC, wherever steam distribution and condensate removal are critical.

• Procurement and Compliance:
  Supports standard terminology in technical procurement and contract documentation, helping ensure compliance with recognized international standards and facilitating global trade of steam system components.

Related Standards

For comprehensive understanding and implementation, prEN ISO 6704:2026 relates to several key standards:

• ISO 6552:
  Provides additional terminology related to steam traps and valves.

• ISO/TC 153 Series:
  Covers broader standards on valves in general, supporting classification, testing, and performance assessment.

• ICS 23.060.01; 23.040.99:
  International Classification for Standards categories supporting broader valve and piping component industry practice.

Summary

prEN ISO 6704:2026 is a foundational document for the classification of automatic steam traps, ensuring clear, standardized categorization throughout steam system applications. Its implementation facilitates uniform communication, reliable specification, and improvement in overall system performance and energy efficiency in industrial steam operations. As organizations strive for operational excellence and energy rationalization, adherence to prEN ISO 6704 is an essential part of best practices for steam system design, operation, and maintenance.

SLOVENSKI STANDARD
01-september-2026
Avtomatski izločevalniki kondenzata - Razvrstitev (ISO/DIS 6704:2026)
Automatic steam traps - Classification (ISO/DIS 6704:2026)
Automatsiche Kondensatorableiter - Klassifizierung (ISO/DIS 6704:2026)
Purgeurs automatiques de vapeur d'eau - Classification (ISO/DIS 6704:2026)
Ta slovenski standard je istoveten z: prEN ISO 6704
ICS:
23.060.01 Ventili na splošno Valves in general
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

DRAFT
International
Standard
ISO/DIS 6704
ISO/TC 153
Automatic steam traps —
Secretariat: AFNOR
Classification
Voting begins on:
Purgeurs automatiques de vapeur d'eau — Classification
2026-06-15
Voting terminates on:
ICS: 23.060.01; 23.040.99
2026-09-07
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
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RECIPIENTS OF THIS DRAFT ARE INVITED
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Reference number
ISO/DIS 6704:2026(en)
DRAFT
ISO/DIS 6704:2026(en)
International
Standard
ISO/DIS 6704
ISO/TC 153
Automatic steam traps —
Secretariat: AFNOR
Classification
Voting begins on:
Purgeurs automatiques de vapeur d'eau — Classification
2026-06-15
ICS: 23.060.01; 23.040.99 Voting terminates on:
2026-09-07
THIS DOCUMENT IS A DRAFT CIRCULATED
FOR COMMENTS AND APPROVAL. IT
IS THEREFORE SUBJECT TO CHANGE
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
IN ADDITION TO THEIR EVALUATION AS
BEING ACCEPTABLE FOR INDUSTRIAL,
© ISO 2026
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
BE CONSIDERED IN THE LIGHT OF THEIR
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RECIPIENTS OF THIS DRAFT ARE INVITED
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TO SUBMIT, WITH THEIR COMMENTS,
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NOTIFICATION OF ANY RELEVANT PATENT
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Published in Switzerland Reference number
ISO/DIS 6704:2026(en)
ii
ISO/DIS 6704:2026(en)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Classification . 1
4.1 General .1
4.2 Mechanical traps .2
4.2.1 Steam trap with closed float .2
4.2.2 Steam trap with closed float without lever .2
4.2.3 Steam trap with open top float (bucket) .3
4.2.4 Steam trap with open inverted float (bucket) .4
4.3 Thermostatic traps, actuated by the temperature of condensate .5
4.3.1 Vapour pressure trap .5
4.3.2 Bimetallic or thermoelastic steam trap .6
4.3.3 Bimetallic steam trap with disc type element .7
4.3.4 Bimetallic steam trap with cantilever element .8
4.4 Thermodynamic traps, actuated by fluid dynamics .9
4.4.1 Disc trap .9
4.4.2 Impulse trap .10
4.4.3 Orifice trap .11

iii
ISO/DIS 6704:2026(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 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
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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/had not] received notice of
(a) patent(s) which may be required to implement this document. However,
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