ISO 6554:1980

Overview

ISO 6554:1980 - Flanged automatic steam traps - Face-to-face dimensions defines standardized face-to-face dimensions for flanged automatic steam traps used in industrial steam piping. The standard covers nominal sizes from DN 15 to DN 50 (with DN 32 retained provisionally) and applies to pressures up to PN 40. It specifies the distance between the two end planes of the trap body (expressed in millimetres) and provides six basic series of face-to-face dimensions in a tabulated form. ISO 6554 applies to the trap body itself and does not cover entire installed assemblies or accessories.

Key topics and requirements

• Face-to-face dimension: the axial distance between the two planes perpendicular to the trap axis at the body end ports (given in mm).
• Nominal size (DN): designation common across piping components (see ISO 6708 for DN definition); ISO 6554 uses DN 15–DN 50 as its scope.
• Six basic dimension series: the standard provides six series of face-to-face lengths to support a range of designs; two of these series are retained only for existing models.
• Pressure rating applicability: dimensions are specified for traps intended for use in systems up to PN 40.
• Scope limitation: applies only to the steam trap components themselves - not to flanges, gaskets, or the entire assembly in-line with the trap.

Practical applications

ISO 6554 is valuable for professionals who need consistent, interchangeable dimensions for flanged steam traps:

• Valve and steam trap manufacturers - to design products that fit standardized piping layouts and are interchangeable with competing products.
• Piping and mechanical engineers - to specify correct trap face-to-face dimensions in engineering drawings and BOMs for steam systems.
• Procurement and maintenance teams - to source replacement traps that fit existing flange spacing without modification.
• Plant designers and contractors - to ensure compatibility of traps with flange patterns and to avoid rework during installation.

By using ISO 6554 dimensions, organizations reduce installation issues, simplify spare-part stocking, and improve interoperability across suppliers.

Related standards

• ISO 6708 - Numerical designation of sizes (DN)
• Work developed under ISO/TC 153 - General purpose industrial valves

Keywords: ISO 6554, flanged automatic steam traps, face-to-face dimensions, DN 15 to DN 50, PN 40, steam trap dimensions, piping standards, valve interchangeability.