ISO/DIS 15500-21:2025(en)

ISO/TC 22/SC 41

Secretariat: UNI

Date: 2025-10-30

Road vehicles — Compressed natural gas (CNG) fuel system components —

Part 21:
Discharge line closures

Véhicules routiers — Composants des systèmes de combustible gaz naturel comprimé (GNC) —

Partie 21: Fermeture des lignes de décharge

© ISO 2025

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Contents

Foreword iv

Introduction v

1 Scope 1

2 Normative references 1

3 Terms and definitions 1

4 Marking 1

5 Construction and assembly 2

6 Tests 2

6.1 Applicability 2

6.2 Continued operation 3

6.3 Internal leakage vent test 3

6.4 Water jet protection 3

Bibliography 4

Foreword

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This document was prepared by Technical ISO/TC 22, Road vehicles, Subcommittee SC 41, Specific aspects for gaseous fuels.

A list of all parts in the ISO 15500 series can be found on the ISO website.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

Introduction

For the purposes of this document, all fuel system components in contact with natural gas have been considered suitable for natural gas as defined in ISO 15403-1. However, it is recognized that miscellaneous components not specifically covered herein can be examined to meet the criteria of this document and tested according to the appropriate functional tests.

All references to pressure in this document are considered to be gauge pressures unless otherwise specified.

This document is based on a service pressure for natural gas used as fuel of 20 MPa [200 bar^[1]] settled at 15 °C. Other service pressures can be accommodated by adjusting the pressure by the appropriate factor (ratio). For example, a 25 MPa (250 bar) service pressure system will require pressures to be multiplied by 1,25.

Road vehicles — Compressed natural gas (CNG) fuel system components — Part 21: Discharge line closures

This document specifies tests and requirements for discharge lines closures, a compressed natural gas (CNG) fuel system component intended for use on the types of motor vehicles defined in ISO 3833.

This document is applicable to vehicles (mono-fuel, bi-fuel or dual-fuel applications) using natural gas in accordance with the ISO 15403-1. It is not applicable to the following:

a) liquefied natural gas (LNG) fuel system components located upstream of, and including, the vaporizer;

b) fuel containers;

c) stationary gas engines;

d) container-mounting hardware;

e) electronic fuel management;

f) refuelling receptacles.

The following documents are referred to in the text in such a way that some or all of their content constitutes requirements of this document. For dated references, only the edition cited applies. For undated references, the latest edition of the referenced document (including any amendments) applies.

ISO 15500‑1, Road vehicles — Compressed natural gas (CNG) fuel system components — Part 1: General requirements and definitions

ISO 15500‑2, Road vehicles — Compressed natural gas (CNG) fuel system components — Part 2: Performance and general test methods

For the purposes of this document, the terms and definitions given in ISO 15500-1 and the following apply.

ISO and IEC maintain terminology databases for use in standardization at the following addresses:

— ISO Online browsing platform: available at https://www.iso.org/obp

— IEC Electropedia: available at https://www.electropedia.org/

3.1

discharge line closure

device used to keep contamination out of a relief line while still permitting escape of gas from the line to the atmosphere

Marking of the component shall provide sufficient information to allow the following to be traced:

a) the manufacturer’s or agent’s name, trademark or symbol;

b) the model designation (part number);

c) the serial number or date code.

The following additional markings are recommended:

— the working pressure or working pressure and temperature range;

— the direction of flow (when necessary for correct installation);

— the type of fuel;

— electrical ratings (if applicable);

— the symbol of the certification agency;

— the type approval number;

— a reference to this document, i.e. ISO 15500-21.

NOTE This information can be provided by a suitable identification code on at least one part of the component when it consists of more than one part.

The discharge line closure shall comply with the applicable provisions of ISO 15500-1 and ISO 15500-2, and with the tests specified in Clause 6. Tolerances should follow the specifications of ISO 15500-2.

Discharge line closures may be single use, such as for pressure relief devices (PRDs), or repeated use, as for pressure relief valves (PRVs). In either case, the discharge line closure is expected to repeatedly vent low flow rates from leakage without losing function.

The tests required to be carried out are indicated in Table 1.

Table 1 — Applicable tests

Discharge line closures intended for repeated use shall pass the following test. Install the device as per the manufacturer's recommended procedure.

Perform 600 cycles of the following, with at least 50 cycles performed at -40 °C or lower and at least 50 cycles at 85 °C or higher. The remainder shall be done between 15 °C and 25 °C. The cycle time shall be (10 ± 2) s.

a) Pressurize the vent line to achieve the manufacturers rated flow for at least two seconds.

b) Stop the flow.

After cycling, the discharge line closure shall pass the water jet protection test in 6.4.

Apply a controlled flow of (30 ± 10) Ncm³/h of nitrogen, air or methane/natural gas to the inlet of the discharge line closure until the pressure stabilizes. The vent line closure shall vent the gas flow without damage and shall not retain more than 0,2 MPa.

Perform the test at -40 °C (+0 °C − 5 °C), room temperature, and 85 °C (−0 °C + 5 °C).

CAUTION — Testing with methane/natural gas could result in dangerous situations. Care should be taken to avoid flammable explosive hazard.

Mount the part as per the manufacturers recommended procedures.

Use a pressure washer having a pressure of (8-10) MPa and a flow rate of at least 14 L/min, and a flat stream nozzle with a fan angle of (10-20)°. Use water at a temperature between 40 °C and 60 °C.

Spray the part directly towards the outlet direction of discharge. If the part is not rotational symmetrical, it or the spray shall be rotated along the axis of discharge at (10-12) s per rotation at each angle of spray. If some angles do not occur in actual use when installed per the manufacturer's recommended procedure those angles may be omitted from the test.

The spray fan orientation, relative to the spray fan spread pattern, shall be perpendicular to the sweep direction. The spray shall come from a nozzle held at a distance of 10 cm to 15 cm from the part. Spraying shall occur at incremental angles of 0°, 30°, 60°, 90°, 120°, and 150° to the axis of rotation symmetry axis for 30 s each.

The part shall not be damaged and shall not allow any water to enter the vent line.

Bibliography

[1] ISO 3833, Road vehicles — Types — Terms and definitions

[2] ISO 15403‑1, Natural gas — Natural gas for use as a compressed fuel for vehicles — Part 1: Designation of the quality

1. 1 bar = 0,1 MPa = 10⁵ Pa 1 MPa = 1 N/mm². ↑