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Scope and General Requirements
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Scope and General Requirements
ANSI Z21.21-2015 (CSA 6.5-2015) establishes uniform safety and performance requirements for automatic valves used in gas appliances. These valves are designed to automatically control the flow of fuel gas based on electrical signals (e.g., from thermostats, timers, or safety controls) or mechanical actuators. The standard covers automatic shut-off valves intended for use in residential, commercial, and industrial gas systems operating at pressures up to 1/2 psi (3.5 kPa) for natural gas and propane.
The scope includes electrically operated valves (solenoid, motorized) and thermally actuated valves (e.g., wax element or bimetallic types). It does not cover manually operated valves, pressure regulators, or valves primarily used in gas distribution piping systems beyond the appliance. The standard is jointly published by the American National Standards Institute (ANSI) and the Canadian Standards Association (CSA), making it applicable in both the United States and Canada.
Key definitions include: automatic valve (a valve that opens or closes automatically in response to a predetermined condition), cycling valve (opens and closes during normal appliance operation), and safety shut-off valve (closes upon loss of power or safety signal). The standard classifies valves based on their intended function and operating environment.
Tip: When referencing the standard, always use the dual designation ANSI Z21.21-2015 • CSA 6.5-2015 to emphasize its binational acceptance.
Technical Specifications and Performance Criteria
Manufacturers must meet rigorous construction, material, and performance requirements to comply with this standard. Below are the key technical requirements:
Construction and Materials
- Materials: All wetted parts in contact with gas must be corrosion-resistant (e.g., brass, stainless steel, engineered polymers) and not degrade under normal gas composition.
- Enclosure: Valves must have a suitable enclosure rated for the intended environment (indoor, outdoor, or vented). Electrical enclosures must meet NEMA or IP ratings as per the manufacturer’s specification.
- Electrical connections: Terminals and wiring must be rated for the valve’s electrical load and comply with NEC or CEC requirements. Grounding provisions are mandatory for metallic enclosures.
Performance Testing
The standard mandates a series of type tests to verify safety and durability. A summary of critical test requirements is presented in the table below.
| Test | Condition | Acceptance Criteria |
|---|---|---|
| Leakage Test (Seat Seal) | Air or inert gas at 1.5 × maximum rated pressure | Leakage ≤ 0.001% of main orifice capacity (e.g., 0.0001 scfh per inch orifice) |
| Leakage Test (External) | Air or inert gas at 1.5 × maximum rated pressure | No visible leakage; pressure drop less than 0.01 psi in 1 minute |
| Endurance (Cycle Life) | 100,000 cycles (or 250,000 for high-cycle valves) | Leakage still within limits; no mechanical wear beyond functional limits |
| Overpressure Test | 2 × maximum rated pressure for 5 minutes | No rupture, permanent deformation, or loss of function |
| Temperature Range | –40°F to 175°F (–40°C to 79°C) ambient | Valve opens and closes at all temperatures; seat leakage remains below limit |
| Response Time (Safety Shut-off) | Power interruption or safety signal | Valve closes within 1 second for solenoid; ≤ 5 seconds for motorized |
Key Compliance: All tests must be performed on production-representative samples, and the manufacturer must maintain a quality management system that ensures ongoing conformity.
Implementation and Installation Considerations
Proper implementation of ANSI Z21.21-2015 valves is critical for system reliability and safety. Here are key points for manufacturers and installers:
- Marking: Each valve must be permanently marked with the manufacturer’s name or trademark, model number, date of manufacture (or code), electrical ratings (volts, amps, frequency), maximum gas pressure, and the standard designation “ANSI Z21.21-2015 • CSA 6.5-2015”.
- Orientation: Unless specified otherwise, valves can be installed in any orientation (vertical, horizontal, or inverted). However, installation instructions must clearly state any orientation restrictions.
- Gas compatibility: Valves certified under this standard are suitable for natural gas, propane, manufactured gas, or LP gas mixtures. If a valve is tested for only one gas type, that must be indicated.
- Wiring and controls: Supply voltage must match the valve rating. For fail-closed valves, ensure the valve closes on loss of power. Do not exceed the valve’s maximum electrical rating.
Warning: Do not use valves without proper overpressure protection upstream. The standard assumes downstream pressure will not exceed the valve’s maximum rated pressure.
Testing in the Field
Field verification of valve operation is recommended during installation and periodic maintenance. Test the valve by interrupting its power supply or control signal and verify positive shut-off using a manometer or electronic leak detector. Never rely solely on the valve’s manual override for shut-off during service.
Danger: A valve that fails to close during testing poses a serious safety risk. Immediately replace it with a certified valve and schedule an inspection of the entire gas train.
Compliance and Certification
To demonstrate compliance with ANSI Z21.21-2015 (CSA 6.5-2015), manufacturers typically seek third-party listing by an accredited certification organization (e.g., CSA Group, Underwriters Laboratories (UL), Intertek). The certification process includes:
- Documentation review: Engineering drawings, bill of materials, and electrical schematics are submitted for review.
- Witnessed testing: A representative from the certifying body witnesses the required type tests at the manufacturer’s facility or an independent laboratory.
- Factory inspection: An initial audit of the manufacturing facility ensures quality control processes are in place.
- Follow-up inspections: Unannounced periodic inspections verify continued compliance. These inspections include random sample testing of production valves.
Valves that pass the certification process receive a listing mark and are eligible for use in installations requiring compliance with the National Fuel Gas Code (NFPA 54) or the Natural Gas and Propane Installation Code (CSA B149.1). Certification is valid as long as the product design does not change, and annual audits are passed.
Tip: Always verify the valve’s listing mark includes the standard number (ANSI Z21.21 • CSA 6.5) and the certifying agency’s logo. This ensures the valve meets the current edition.
Frequently Asked Questions
Q: Do ANSI Z21.21-2015 valves need to be installed by a licensed professional?
A: The standard itself does not mandate installation personnel qualifications, but local codes (e.g., NFPA 54, CSA B149.1) typically require gas work to be performed by a qualified installer. Always follow local regulatory requirements.
A: The standard itself does not mandate installation personnel qualifications, but local codes (e.g., NFPA 54, CSA B149.1) typically require gas work to be performed by a qualified installer. Always follow local regulatory requirements.
Q: What is the difference between a cycling valve and a safety shut-off valve under this standard?
A: A cycling valve is designed for normal on/off control during appliance operation (e.g., burner cycling). A safety shut-off valve is designed to close upon a safety signal (e.g., high temperature, gas leak) or upon loss of power, providing an additional layer of protection. The standard has separate endurance tests (cycling vs. safety closing) for each type.
A: A cycling valve is designed for normal on/off control during appliance operation (e.g., burner cycling). A safety shut-off valve is designed to close upon a safety signal (e.g., high temperature, gas leak) or upon loss of power, providing an additional layer of protection. The standard has separate endurance tests (cycling vs. safety closing) for each type.
Q: Are remote-operated valves covered by this standard?
A: Yes, as long as the valve automatically opens and closes in response to an electrical or mechanical signal. This includes valves with wireless or wired remote controls. However, any wireless communication must also comply with applicable wireless standards (e.g., FCC Part 15).
A: Yes, as long as the valve automatically opens and closes in response to an electrical or mechanical signal. This includes valves with wireless or wired remote controls. However, any wireless communication must also comply with applicable wireless standards (e.g., FCC Part 15).
Q: How often should a certified valve be re-tested in the field?
A: The standard does not specify a field-testing interval. However, industry best practice recommends checking automatic gas valves at least once a year during appliance maintenance. Valves found leaking or failing to close should be replaced immediately.
A: The standard does not specify a field-testing interval. However, industry best practice recommends checking automatic gas valves at least once a year during appliance maintenance. Valves found leaking or failing to close should be replaced immediately.
First published 2015. This article references the 2015 edition of ANSI Z21.21 / CSA 6.5. Standard revision years are subject to periodic updates. Always verify the current version from ANSI or CSA. © 2026
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