ISO 3601-2:2025

Overview

ISO 3601-2:2025 - Fluid power systems - O-rings - Part 2: Housing dimensions for general applications specifies recommended groove and mating-surface dimensions for class A O‑rings (general industrial) and selected class B O‑rings for metric hardware (e.g., cylinder bores and piston rods). It applies to hydraulic and pneumatic systems, for configurations with and without anti‑extrusion (back‑up) rings, and aligns O‑ring dimensions (d1, d2), size codes (SC) and tolerances with ISO 3601-1.

The standard provides tabulated housing dimensions and two design approaches:

• Design hardware around a chosen O‑ring (Tables 3, 5, 8).
• Select an O‑ring to fit fixed hardware (Tables 4, 6).

Annex A covers aerospace correlations and Annex B gives volumetric methods for calculating housing fill.

Key Topics

• Groove geometry and symbols: definitions for housing width, groove depth, radial depth, gaps, chamfers and edge radii.
• Surface roughness and finish: specified roughness parameters, material ratio guidance (Rmr) and prohibition of defects (scratches, nicks, spiral marks) that reduce seal life.
• Anti‑extrusion (back‑up) rings: housing widths and layout for no, one or two back‑up rings; reference to ISO 3601‑4 for detailed recommendations.
• Design methods: tabular guidance for O‑ring-first vs hardware‑first design; calculation of effective compression, diametral stretch and volumetric housing fill (Annex B).
• Tolerancing and run‑out: tolerancing per ISO 8015 and run‑out limits for different diameters.
• Application types: dynamic piston and rod seals, static axial/face seals, and relevant dimension variants.
• Environmental/operational considerations: housing fill, temperature effects and need to agree special dimensions with O‑ring manufacturers.

Applications and Users

ISO 3601-2:2025 is essential for:

• Seal designers and OEMs specifying groove geometry for hydraulic/pneumatic cylinders and valves.
• Mechanical engineers designing piston/rod assemblies and face seals.
• Seal manufacturers and suppliers choosing or recommending O‑ring sizes for metric hardware.
• Maintenance, procurement and quality teams ensuring correct housing tolerances and surface finishes.
• Aerospace designers referencing Annex A for aerospace‑grade O‑ring housings.

Using this standard helps prevent extrusion, reduce leakage risk, improve seal life and streamline component interoperability in fluid power systems.

Related Standards

• ISO 3601‑1 - O‑ring sizes, cross‑sections and codes (normative reference)
• ISO 3601‑4 - Use of anti‑extrusion rings (back‑up rings)
• ISO 5598 - Fluid power vocabulary
• ISO 21920‑2 - Surface roughness/material ratio guidance
• ISO 8015 - General tolerancing principles

Keywords: ISO 3601-2:2025, O‑ring housing dimensions, fluid power systems, hydraulic seals, pneumatic seals, anti‑extrusion rings, groove design, surface roughness, housing fill.