FUGITIVE EMISSIONS
Figure 2: Stem sealing system- material, ring architecture and interface.
material properties are fundamental, they represent only one part of the overall system. Reliable fugitive emission performance results from the interaction of multiple parameters. The material system defines resistance to temperature, oxidation and media. The ring construction determines conformability, recovery behaviour and friction characteristics. The valve interface, including stem surface quality, stuffing box geometry and tolerances, governs how effectively these properties translate into sealing performance. Figure 2 illustrates this system perspective by showing how the packing material system, ring architecture and the interface between stem, packing and stuffing box together define the behaviour of the stem sealing system. Only when these elements are aligned can predictable leakage behaviour be achieved
Material → Packing Material System
Design → Ring Architecture
Interface → Stem / Packing / Stuffing Box
across repeated operating cycles. In many applications, live-loading can further stabilise the system by compensating for relaxation effects and maintaining a more consistent sealing force. However, such measures are only effective when integrated into the overall sealing concept rather than applied as corrective solutions.
Application requirements must be addressed early
A decisive factor for long-term performance is the timing of engineering decisions. In practice, sealing behaviour is strongly influenced by how early operating conditions, installation requirements and valve characteristics are considered. Close cooperation between OEMs, operators and packing manufacturers is therefore essential. Parameters such as cycling
frequency, temperature range, stem quality, media compatibility and maintenance philosophy must be clearly defined at an early stage. If this alignment happens too late, even advanced packing systems may not achieve their intended performance in service.
Critical media reveal the limits of simplified qualification logic
Applications involving critical media make the limitations of a purely standard-driven approach particularly evident. Oxygen service illustrates this clearly. While leakage control remains important, additional factors such as material cleanliness, ignition resistance and friction behaviour become equally decisive. A packing that meets general emission limits may still be unsuitable if it has not been specifically engineered and qualified for such conditions. This highlights a broader principle: low measured leakage alone does not guarantee application suitability. The entire sealing system must be designed and validated for the specific duty.
Stability over time is the key indicator
The evaluation of next-generation valve packing must therefore focus not only on achieving low leakage, but on maintaining it. This behaviour can be illustrated using a high-performance packing system such as Burgmann Packings’ BPG 7888. Under ISO 15848 test conditions, the packing demonstrates stable leakage behaviour over extended thermal and mechanical cycling, without measurable leakage
Figure 3: Leakage behaviour of the BPG 7888 packing system under ISO 15848 test conditions.
42 Valve World October 2026 www. valve-world. net