oSIST prEN ISO 6704:2026

• 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
• Public Enquiry End Date: 14-Sep-2026
• ICS: 23.060.01 - Valves in general
• Technical Committee: TLP - Pressure vessels
• Current Stage: 4020 - Public enquire (PE) (Adopted Project)
• Start Date: 21-Jul-2026
• Due Date: 08-Dec-2026
• Ref Project: prEN ISO 6704 - Automatic steam traps - Classification (ISO/DIS 6704:2026)

• Revises: SIST EN 26704:2000 - Automatic steam traps - Classification (ISO 6704:1982)
• Effective Date: 01-Sep-2026

Overview

oSIST prEN ISO 6704:2026 - Automatic steam traps - Classification - provides a clear, internationally recognized classification system for automatic steam traps. Developed by the Slovenian Institute for Standardization (SIST), this draft European standard aligns closely with ISO/DIS 6704:2026 and aims to simplify communication and compatibility across the global steam systems industry.

Automatic steam traps are essential components in steam systems, ensuring the efficient removal of condensate while preventing steam loss. This standard classifies automatic steam traps purely by the mode of actuation for their obturation (shut-off) device, independent of design or construction details. This simplified categorization enables manufacturers, operators, and maintenance teams to select, specify, and compare steam traps more effectively.

Key Topics

• Classification by Actuation: The standard recognizes three primary categories of automatic steam traps:

  • Mechanical traps: Operated by condensate level.
  • Thermostatic traps: Operated by condensate temperature.
  • Thermodynamic traps: Operated by fluid dynamics.

• Mechanical Traps:

  • Closed float traps (with or without lever)
  • Open float (bucket) traps
  • Inverted bucket traps

• Thermostatic Traps:

  • Vapour pressure traps (balanced pressure)
  • Bimetallic or thermoelastic traps
  • Bimetallic disc and cantilever element traps

• Thermodynamic Traps:

  • Disc traps
  • Impulse traps
  • Orifice traps

• Terminology and Definitions: Key terms, such as "obturator" and "automatic steam trap", are defined to foster a common language for both manufacturers and end users.

Applications

oSIST prEN ISO 6704:2026 is highly relevant in a range of industrial sectors where steam is used for heating, process operations, or power generation. Its practical applications include:

• Steam System Design: Enables system designers and engineers to specify appropriate steam trap categories for different parts of a plant or network based on operating conditions.
• Maintenance and Operations: Facilitates identification and replacement of steam traps by maintenance teams, reducing downtime and improving system reliability.
• Procurement and Specification: Helps procurement professionals compare products by clear, function-based classification rather than design specifics.
• Energy Efficiency: By ensuring the correct trap is chosen and maintained, the standard supports optimal condensate removal and steam utilization, resulting in cost savings and reduced energy waste.
• Global Trade and Compliance: Harmonizes technical language for international commerce, helping manufacturers and operators demonstrate compliance with recognized European and ISO standards.

Related Standards

For comprehensive management and design of steam systems, users may refer to the following related standards:

• ISO 6552 - Definitions of terms relating to steam traps
• EN 10226 - Pipe threads where pressure-tight joints are made on the threads
• ISO 6704:1982 - Superseded version of this classification standard
• ICS 23.060.01 - Valves in general
• Other ISO/EN steam trap test and performance standards for specific requirements concerning performance, safety, and interoperability

oSIST prEN ISO 6704:2026 thus provides essential guidance for anyone involved in design, operation, or maintenance of steam systems, supporting global consistency, regulatory compliance, and energy efficiency through a unified classification approach.

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
AND MAY NOT BE REFERRED TO AS AN
INTERNATIONAL STANDARD UNTIL
PUBLISHED AS SUCH.
This document is circulated as received from the committee secretariat.
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BEING ACCEPTABLE FOR INDUSTRIAL,
TECHNOLOGICAL, COMMERCIAL AND
USER PURPOSES, DRAFT INTERNATIONAL
STANDARDS MAY ON OCCASION HAVE TO
ISO/CEN PARALLEL PROCESSING
BE CONSIDERED IN THE LIGHT OF THEIR
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS.
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 SUPPORTING DOCUMENTATION.
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
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
POTENTIAL TO BECOME STANDARDS TO
WHICH REFERENCE MAY BE MADE IN
or ISO’s member body in the country of the requester.
NATIONAL REGULATIONS.
ISO copyright office
RECIPIENTS OF THIS DRAFT ARE INVITED
CP 401 • Ch. de Blandonnet 8
TO SUBMIT, WITH THEIR COMMENTS,
CH-1214 Vernier, Geneva
NOTIFICATION OF ANY RELEVANT PATENT
Phone: [phone]
RIGHTS OF WHICH THEY ARE AWARE AND TO
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Email: [e-mail]
Website: www.iso.org
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
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