Fugitive emissions from valves account for 60 to 80 percent of total plant fugitive emissions. Valve stem seals leak volatile organic compounds and methane during operation, and packing degrades through thermal cycling, mechanical wear, and chemical attack. Standards organizations developed qualification protocols that test valve designs under accelerated aging — but the certification landscape is fragmented across API and ISO frameworks that are often confused or wrongly treated as interchangeable.
This article breaks down what each standard covers, what a certificate proves, and how to specify low-emission valves without gaps in your procurement package.
API 622: Packing Qualification First
API 622 is not a valve standard. It qualifies the packing material itself through thermal cycling, mechanical cycling, and leak testing at elevated temperature using methane as the test fluid.
Manufacturers select API 622-qualified packing before pursuing API 624 or API 641 certification. An API 622 passing result does not mean a completed valve will pass API 624 or 641 — the packing qualification is a prerequisite, not a substitute for the valve test.
API 624: Rising Stem Valves
API 624, "Type Testing of Rising Stem Valves Equipped with Graphite Packing for Fugitive Emissions," applies to gate valve, globe valve, and other rising-stem designs. The protocol subjects a representative valve to mechanical cycles and thermal cycles at elevated temperature, measuring leakage at the stem seal using EPA Method 21.
The acceptance threshold is 100 ppm methane measured at the stem-packing interface during designated test phases. The standard requires three thermal cycles and a defined number of mechanical cycles at ambient and elevated temperature. A design that passes API 624 has demonstrated that its packing configuration, stem finish, and body seal geometry contain emissions under the specified test conditions.
API 641: Quarter-Turn Valves
API 641, "Type Testing of Quarter-Turn Valves Equipped with Graphite Packing for Fugitive Emissions," covers ball valve and butterfly valve designs — any valve where the stem rotates rather than rises. The methodology mirrors API 624: EPA Method 21 monitoring, methane test fluid, defined thermal and mechanical cycling, and a 100 ppm acceptance criterion.
The test validates the stem packing system under quarter-turn motion, where packing sees different stress distributions than in rising-stem designs.
ISO 15848: The International Framework
ISO 15848 is a two-part standard. Part 1 covers type testing of valve designs. Part 2 covers production acceptance testing.
ISO 15848-1: Type Testing
ISO 15848-1 classifies valves by tightness class, endurance class, and temperature range. Tightness classes are labeled A, B, and C — class A being the most stringent. Endurance classes define the number of mechanical cycles the valve must complete. The standard uses helium or methane as test gas and measures leakage with sniffing or vacuum techniques.
Unlike API 624 and 641, ISO 15848-1 does not prescribe a single pass/fail threshold. The qualification result states which tightness and endurance classes the valve achieved. Buyers must specify the required class — writing "ISO 15848 certified" without stating the class is incomplete.
ISO 15848-2: Production Acceptance
ISO 15848-2 defines production leak testing for valves manufactured to a qualified design. This is the production-level check confirming each valve meets the same sealing principles validated in the type test. Part 2 testing is less severe than Part 1 but provides the per-unit verification that type testing alone does not.
API vs ISO: Not Interchangeable
API 624/641 and ISO 15848 are separate frameworks. A valve qualified to API 624 is not automatically certified to ISO 15848-1, and vice versa. The test fluids, cycling protocols, leakage measurement methods, and acceptance logic all differ.
API standards use methane, EPA Method 21, and a fixed 100 ppm threshold. ISO 15848-1 uses helium or methane, allows multiple measurement techniques, and reports tightness classes rather than a single pass/fail. If a spec calls for ISO 15848, an API 624 certificate does not satisfy it.
TA-Luft and VDI 2440
German TA-Luft (Technical Instructions on Air Quality) and VDI 2440 are older emission-limit frameworks referenced in European installations. TA-Luft remains relevant in European regulatory contexts but is increasingly superseded by ISO 15848 internationally. If a project references TA-Luft, verify whether ISO 15848 acceptance is also required.
What a Certificate Actually Proves
A type test certificate under API 624, API 641, or ISO 15848-1 proves that a specific valve design — with a defined packing configuration, stem material, and body style — passed a defined test protocol. It is a design qualification, not a production quality guarantee.
Stem surface finish, packing installation torque, and body bolt tensioning all vary in production. This is why ISO 15848-2 production testing and end-user specified production leak testing matter. A full flowks valve low-emission package includes the type test certificate plus production leak testing on every unit.
How to Specify Low-Emission Valves on Datasheets
Engineers and buyers should include the following in valve datasheets:
- State the exact standard and edition: "API 624, 4th Edition" or "ISO 15848-1:2015, Tightness Class B, Endurance Class CO2"
- Specify packing details: packing type, manufacturer, and confirmation that the packing is API 622 qualified
- Define stem finish requirements: surface roughness, lay direction, and hardfacing if applicable
- Require production leak testing: reference ISO 15848-2 or specify a production leak test protocol with acceptance criteria
- Identify the test fluid and measurement method if deviating from the standard default
Common Specification Mistakes
Writing "API 624 compliant" without stating the edition. Acceptance criteria changed between editions — always cite the specific revision.
Accepting an API 622 packing test report as proof that the valve passes API 624. The packing test is not the valve test.
Mixing API and ISO terminology in the same specification — for example, requesting "API 624, Tightness Class B." Tightness classes are ISO 15848 terminology, not API. This signals that the specifier may not understand the distinction.
Omitting production testing requirements entirely. Without ISO 15848-2 or an equivalent production leak test, per-unit emission performance is unverified.
FLOWKS manufactures a full range of industrial valves — ball valves, control valves, gate valves, globe valves, check valves, strainers, knife gate valves, and plug valves — with low-emission packing systems available across all rising-stem and quarter-turn product lines. Contact FLOWKS for certified low-emission valve solutions built to API 624, API 641, and ISO 15848 standards.
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