What are the characteristics of the static seal design of the fire extinguisher valve

In the design and manufacturing process of modern fire extinguishers, static seal design plays a vital role. This design is not only related to the overall performance of the fire extinguisher, but also directly affects its reliability and safety at critical moments. The core of static seal design lies in the structural optimization of the sealing interface, and high-precision processing technology is usually used to ensure that the sealing surface is flat, vertical and smooth. Through CNC turning, grinding and polishing and other process treatments, the sealing surface can achieve micron-level tolerance control, effectively avoiding sealing failure caused by microscopic unevenness.

In the connection part between the valve body and the bottle mouth, metal thread combination is generally adopted. By embedding a sealing gasket or a sealing ring at the bottom of the interface, an axial or radial compression sealing structure is formed, thereby ensuring that the sealing material is evenly compressed during the tightening process to form an effective sealing barrier. Common sealing structures include plane seals, conical seals and spherical seals. Among them, the conical seal is particularly suitable for high-pressure static sealing occasions because of its characteristics of automatic centering and high line contact pressure, and is widely used in various types of fire extinguishers.

The selection of sealing materials is a key factor that cannot be ignored in static seal design. Different types of fire extinguishing agents have different requirements for the compatibility of sealing materials. For example, dry powder fire extinguishers require sealing materials to have good resistance to abrasive erosion, while carbon dioxide fire extinguishers require materials to maintain good flexibility and elasticity at extremely low temperatures. In addition, clean gas fire extinguishers require sealing materials to have extremely low gas permeability and excellent anti-aging properties. Fluororubber is widely used in various high-performance static sealing parts due to its excellent resistance to high temperature, oil and chemical corrosion; EPDM is suitable for water-based fire extinguishing agent systems, showing good water resistance and anti-ozone aging performance; polytetrafluoroethylene is often used in static sealing parts in contact with highly corrosive gases due to its extremely low friction coefficient and high corrosion resistance. In order to improve the stability and durability of the seal, some high-end products add metal skeletons or fiber reinforcement layers to the sealing gaskets to improve the structural strength and prevent the seals from being extruded or deformed under long-term high pressure.

In terms of design details, size matching and compression rate control of the static sealing area are crucial. The width, depth and compression ratio of the sealing ring groove must be accurately calculated to ensure that the sealing material reaches a balanced state after assembly, neither over-pressuring to cause permanent deformation nor under-compressing to cause sealing failure. In general, the compression rate of static seals should be controlled between 20% and 30%, which can provide sufficient sealing stress while maintaining the resilience of the rubber material. In addition, for threaded connections, the sealing design must also consider anti-loosening measures to prevent loosening caused by vibration or temperature changes, resulting in relaxation and leakage of the sealing interface.

The static sealing performance of fire extinguisher valves must meet strict testing standards and certification requirements. International mainstream standards such as UL, EN3, GB4351, etc. have proposed specific test methods and leakage limits for the static airtightness performance of fire extinguishers. Usually, a pressurized airtight test is used to fill the fire extinguisher with dry air or nitrogen at rated pressure or even higher pressure (for example, 1.5 times the working pressure), and use soapy water or a special bubble detector to observe the static sealing interface. If continuous bubbles appear, it is judged as a leak failure. Some high-end products also use helium mass spectrometry leak detection technology to perform trace detection of static seal leakage rates, with a sensitivity of up to 10⁻⁷ Pa·m³/s, designed to verify fire extinguishing system products with extremely high sealing performance requirements.