prEN ISO 6704

prEN ISO 6704 is a draft European adoption of ISO/DIS 6704:2026 on automatic steam traps. It gives a simple classification of the main trap types by how the obturation device is actuated. Engineers, buyers, and maintenance teams use it to name, compare, and specify steam traps consistently.

What does prEN ISO 6704 specify?

prEN ISO 6704 specifies a classification of the main types of automatic steam traps according to the mode of actuation of their obturation device. It classifies the traps by operating principle and leaves out details of design and construction, so the document is about naming and grouping types rather than measuring performance.

The document is organized into:

• Scope
• Normative references
• Terms and definitions
• Classification

Clause 4 is the core of the document. It splits automatic steam traps into mechanical, thermostatic, and thermodynamic categories, and then lists the named types within each category.

What are the key requirements of prEN ISO 6704?

prEN ISO 6704 classifies automatic steam traps by actuation principle, not by shape, size, or internal construction. In practice, that means a product is identified by how it opens and closes, which helps users compare products from different manufacturers on the same basis.

Mechanical traps

Clause 4.2 covers mechanical traps, which are actuated by the level of condensate. The document names four forms: closed float, closed float without lever, open top float (bucket), and open inverted float (bucket).

These names matter because they describe the operating mechanism a buyer or specifier needs to match to the application. For example, the figures show whether the float acts through a lever or directly, which affects how the trap should be described in catalogs and technical files.

Thermostatic traps

Clause 4.3 covers thermostatic traps, which are actuated by the temperature of the condensate. The types listed are vapour pressure trap, bimetallic or thermoelastic steam trap, bimetallic steam trap with disc type element, and bimetallic steam trap with cantilever element.

This classification matters when the operating temperature range is important. The document ties each name to the temperature-sensitive element, so users can state which thermal mechanism they are selecting.

Thermodynamic traps

Clause 4.4 covers thermodynamic traps, which are actuated by fluid dynamics. The document names disc trap, impulse trap, and orifice trap.

In practice, this lets users distinguish traps by how pressure changes and flow behavior produce opening or closing movements. That is useful when comparing products that may look similar but work differently.

General rule for the classification

Clause 4.1 says that combined or new designs may exist, but they are not treated as characteristic types in the sense of this document. In practice, that keeps the classification focused on the recognized main families and avoids mixing hybrid designs into the basic naming scheme.

What terms does prEN ISO 6704 define?

Automatic steam trap - A self-contained valve that drains condensate from a steam-containing enclosure while staying tight to live steam or, if needed, allowing steam to pass at a predetermined rate.

Obturator - The movable valve component that permits, restricts, or blocks fluid flow.

Mechanical trap - A trap that responds to the level of condensate.

Thermostatic trap - A trap that responds to the temperature of the condensate.

Thermodynamic trap - A trap that responds to fluid dynamics.

Vapour pressure trap - A thermostatic trap in which pressure imbalance between condensate and a volatile liquid in a deformable element drives the valve movement.

Bimetallic or thermoelastic steam trap - A thermostatic trap in which temperature changes deform a bimetallic or thermostatic element to open or close the valve.

Who uses prEN ISO 6704?

prEN ISO 6704 is used by steam-trap manufacturers, system designers, plant engineers, maintenance teams, quality managers, and buyers. They use it to classify products, write specifications, compare alternative designs, and communicate clearly about steam-trap types in industrial steam systems.

It is also useful when technical documents, catalogues, or procurement records need a common vocabulary for automatic steam traps. That reduces confusion between traps that have similar functions but different actuation principles.

What changed in prEN ISO 6704 from the previous edition?

prEN ISO 6704 is the second edition and it cancels and replaces ISO 6704:1982. The foreword states that the document was technically revised.

The stated changes are:

• a new definition of obturator was added
• new types were added for the closed float without lever, open top float (bucket), bimetallic steam trap with disc type element, and bimetallic steam trap with cantilever element
• in the thermodynamic section, disc trap replaced the earlier wording “obturator trap”
• in the orifice-based type, “labyrinth or orifice trap” was replaced by “orifice trap”
• liquid or solid expansion trap was deleted

Which standards are used with prEN ISO 6704?

Clause 3 uses ISO 6552 for the terms and definitions that apply to this document. The introduction also says prEN ISO 6704 is intended to be read with other International Standards that use these terms and expressions to describe the technical characteristics or performances of an automatic steam trap.

What does the prEN ISO 6704 document contain?

The document is mainly a classification standard, not a test method or performance standard. Clause 4 is supported by figures for each trap family and subtype, showing the main parts such as the obturator, seat, lever, pressure chamber, and flow direction.

Those figures help users identify and label the different trap types in technical documents, product literature, and specifications. The document also includes a short term-definition section that anchors the classification in common vocabulary.