What anti-corrosion treatment is required for the internal and external surfaces of the fire extinguisher valve

Fire extinguisher valves are critical components of fire extinguisher pressure vessels, directly controlling the release of extinguishing agents. Their corrosion resistance is directly related to the functional reliability and long-term safety of the fire extinguisher. The valve's internal and external surfaces must undergo sophisticated corrosion protection to withstand the chemical attack of the extinguishing agent itself, the high-pressure gas environment, and the rigors of external storage conditions. These treatments are designed to ensure the valve's structural integrity and operational performance throughout its lifecycle, minimizing the risk of failure.

Corrosion Protection of Valve Internal Surfaces: Resisting Chemical Attack by Fire Extinguishing Agents
The internal surfaces of valves, which come into direct contact with the extinguishing agent and actuating gas, are of paramount importance in corrosion protection. Different extinguishing agents have different chemical properties, requiring tailored internal protection.

1. For Water-Based and Foam Fire Extinguishers
Water-based and foam fire extinguishing agents are typically acidic or alkaline and contain water, which can lead to strong electrochemical corrosion of common valve body materials such as brass and aluminum alloys.

Electroless Nickel Plating: This is a chemical deposition technology that does not rely on an external electrical current. The plating layer is extremely dense and uniform, completely covering the complex internal cavity and threads of the valve, forming a reliable physical barrier. The nickel plating also offers excellent wear resistance, protecting the valve interior from erosion caused by high-velocity fire extinguishing agent particles.
Epoxy Lining: Certain high-pressure valves requiring extreme corrosion resistance may be lined with a high-performance epoxy resin coating. This coating effectively isolates ions in water-based fire extinguishing agents, preventing electrochemical reactions. Key to this is the coating's adhesion and pinhole-free properties.
Stainless Steel Selection: For critical internal components exposed to the most corrosive water-based or wet chemical fire extinguishing agents, such as siphon connections, 304 or 316 grades of stainless steel are typically selected for inherent corrosion resistance.
2. For Dry Powder Fire Extinguishers
While dry powder fire extinguishers (such as ABC) are less corrosive in dry environments, they can form acidic or alkaline solutions when exposed to moisture, corroding metals. Furthermore, friction and accumulation of dry powder particles can affect the proper opening of the valve. Polytetrafluoroethylene Coating: PTFE coating is widely used on the inner surfaces and key moving parts (such as pistons and stems) of dry powder fire extinguisher valves. PTFE offers excellent chemical inertness, low friction, and non-stick properties, providing corrosion resistance while preventing dry powder particles from adhering to the valve interior, ensuring smooth discharge during emergencies.

Anti-Corrosion Treatment of Valve External Surfaces: Resisting Environmental Factors
Valve external surfaces are exposed to storage environments and need to withstand humidity, salt spray, UV rays, and mechanical damage. The primary goals of external surface treatment are aesthetics, durability, and legible markings.
1. Anodizing and Passivation
For aluminum alloy valve bodies: Anodizing is the most commonly used surface treatment for aluminum alloy valves. It uses an electrochemical reaction to create a thick, hard aluminum oxide film on the aluminum surface. This film not only significantly improves the valve body's weather resistance and hardness, but can also be dyed to achieve color coding, such as red or black, to match product appearance requirements.
For stainless steel components: Exposed stainless steel components require passivation. This is a chemical cleaning process designed to remove surface impurities and free iron, naturally forming a more stable, more complete protective chromium oxide film on the stainless steel surface, maximizing its resistance to rust in humid environments.
2. Plating Protection
Chrome Plating: For brass or zinc alloy valve bodies, chrome plating provides a hard, glossy, and wear-resistant surface. It is often used on externally visible components, providing both protection and a visually appealing effect.
Galvanizing: Galvanizing is commonly used on small parts such as steel fasteners and internal springs on valves. The zinc layer acts as a sacrificial anode, preferentially corroding when corrosion occurs, thus protecting the underlying steel from oxidation.
3. Powder Coating
Powder coating is an environmentally friendly and durable surface treatment technology. Powder coating is applied to the exterior of the valve using electrostatic attraction and then cured at high temperature to form a strong protective film.
Benefits: This coating offers excellent impact, UV, and scratch resistance. It effectively blocks moisture and contaminants, preventing environmental corrosion, and is available in a variety of colors to match the color of the fire extinguisher cylinder.

Special Protection for Seals and Threads
Fire extinguisher valve failure often begins with corrosion in the threads and sealing areas.
Thread Lubrication and Anti-Seize Compound: In addition to surface coating, the threads connecting the valve body to the cylinder are typically coated with a specific thread sealant or anti-seize compound. This not only helps maintain airtightness but also prevents cold welding or corrosion seizure of the threads under high temperature or high pressure, ensuring safe disassembly during maintenance and hydrostatic testing.
Material Upgrades for Critical Seals: As mentioned earlier, seals such as O-rings and gaskets are not plated. Instead, they are constructed from chemically resistant elastomers, such as EPDM (ethylene propylene diene monomer), Viton, or nitrile rubber, to ensure long-term compatibility with fire extinguishing agents and actuating gases. This is crucial for ensuring long-term zero-leakage valve operation.