ISO 15500-12:2015

Overview

ISO 15500-12:2015 specifies tests and requirements for the pressure relief valve (PRV) used in compressed natural gas (CNG) fuel systems for road vehicles defined in ISO 3833. It applies to vehicles using natural gas in accordance with ISO 15403-1 (mono‑fuel, bi‑fuel or dual‑fuel applications) and focuses on ensuring safe, reliable operation and traceability of PRVs. References to pressure are gauge pressures unless otherwise stated, and the part is based on a nominal service pressure of 20 MPa (200 bar) at 15 °C.

Key Topics

• Scope and applicability

  • PRVs for CNG vehicle fuel systems; not applicable to LNG components upstream of the vaporizer, fuel containers, stationary gas engines, container mounting hardware, electronic fuel management or refuelling receptacles.

• Marking and traceability

  • Components shall be marked to allow tracing to the manufacturer, model designation, working pressure and temperature range. Recommended additional markings include flow direction, fuel type, certification symbol, type approval number and serial/date code.

• Construction and assembly

  • PRVs must comply with the general provisions in ISO 15500-1 and ISO 15500-2. Tolerances follow ISO 15500-2 specifications.

• Required tests (as specified in Clause 6):

  • Hydrostatic strength - test to at least 2,5 times the working pressure; mechanism removed and orifice blocked for the test.
  • Leakage - tested at working pressure and across temperature conditions (e.g. −40 °C or −20 °C, room temperature, and 85 °C or 120 °C as applicable).
  • Continued operation - PRV must withstand 600 cycles; cycle defined by pressurizing to set pressure to open and vent, then reducing pressure until re‑seating. After cycling, leakage test at 20 °C ± 5 °C.
  • Operational test - verify opening and re‑seating pressures. At 20 °C opening pressure must be ±5 % of set pressure; re‑seating ≥ 90 % of set pressure (with wider tolerances at extreme temperatures).
  • Additional tests include corrosion, ageing, vibration, compatibility and automotive fluids as required.

• Test media

  • Air, nitrogen or natural gas may be used; if not natural gas, flow values must be corrected to natural gas.

Applications

This part of ISO 15500 is targeted at manufacturers, test laboratories, vehicle OEMs and certification bodies working with CNG vehicle fuel systems. Implementing these requirements supports:

• Safer venting under overpressure conditions
• Consistent operational performance across temperatures
• Regulatory and type‑approval compliance
• Clear component identification for service and recalls

Related Standards

• ISO 15500-1: General requirements and definitions
• ISO 15500-2: Performance and general test methods
• ISO 3833: Road vehicle types and definitions
• ISO 15403-1 and ISO/TR 15403-2: Natural gas quality for vehicles

For detailed procedural steps and acceptance criteria, consult ISO 15500-12:2015 and the referenced parts of the ISO 15500 series.