ISO 20766-9:2019

Overview

ISO 20766-9:2019 specifies requirements for pressure relieve devices (PRDs) used in liquefied petroleum gas (LPG) vehicle fuel systems. It covers definitions, general design principles, marking and instruction requirements, and mandatory test methods to verify safety and long-term performance. The standard applies to LPG systems for road vehicles defined in ISO 3833 (mono‑fuel, bi‑fuel or dual‑fuel) and to PRDs with service pressures in the range of 110 kPa to 840 kPa (gauge pressures), with other pressures accommodated by proportional adjustment.

Key topics and technical requirements

• Scope & applicability: For vehicle LPG fuel system components (excluding fuel containers, stationary engines, container mounting hardware, electronic fuel management and refuelling receptacles).
• Marking requirements: Mandatory traceable markings include manufacturer/agent name, model/part number and working pressure (or pressure and temperature range). Recommended markings include flow direction, fuel type, electrical ratings, certification symbol, type approval number and serial/date code.
• Construction & assembly: PRDs must meet the general construction provisions of ISO 20766-1 and ISO 20766-2 and the specific tests listed in this part.
• Mandatory tests (see Clause 6): hydrostatic strength (test pressure = 2.5 × working pressure), leakage (at several temperatures and pressure factors), bending moment (for externally-threaded designs), continued operation (cyclic testing), accelerated life (to assess fusible material creep), benchtop activation (thermal activation test up to 600 °C), thermal cycling, condensate-corrosion resistance and flow capacity.
• Accelerated-life criteria: Designed to verify reliable operation for at least 1 year at 82 °C and 20 years at 57 °C. The standard gives a formula to derive the accelerated-life temperature TL from the manufacturer’s specified activation temperature Tf and requires specific time‑to‑activation thresholds for test samples.
• Activation controls: Defines activation pressure and activation temperature as manufacturer-specified parameters and requires PRDs to demonstrate consistent activation behavior throughout life and after environmental and mechanical stress.

Applications and who uses it

ISO 20766-9 is used by:

• LPG component manufacturers (design, type approval and production testing)
• Vehicle OEMs integrating LPG fuel systems
• Certification and homologation bodies assessing PRD compliance
• Testing laboratories performing functional, durability and safety tests
• Safety engineers and fleet operators specifying PRDs for vehicle conversion or manufacture

Related standards

• ISO 20766-1 - General requirements and definitions for LPG fuel system components
• ISO 20766-2 - Performance and general test methods for LPG components
• ISO 3833 - Vehicle classification (applicability)
• ISO 9162 - Gaseous fuels - specifications referenced for fuel compatibility

This standard ensures PRDs for LPG vehicle systems meet traceability, mechanical, thermal and long‑term performance requirements-critical for safe pressure relief and vehicle safety compliance.