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Marine butterfly valves and water treatment butterfly valves, although both bear the name "butterfly valve", their core principles are both to control the flow of fluids by rotating the butterfly plate. However, due to the completely different fields they serve, there are significant differences in design philosophy, material selection, and testing certification. It can be said that one is a "special soldier" designed to cope with harsh marine environments, while the other is a "general guardian" serving the water systems on land.
I. Core Mission and Operating Environment: Harsh Oceans vs. Diverse Landscapes
Marine Butterfly Valve:
Its core mission is to ensure the absolute safety and reliable operation of the isolated floating vessel. It operates in a highly corrosive marine environment: the air is rich in salt, and it is humid. The valve body may be directly immersed in seawater or be exposed to seawater spray for long periods. Moreover, during navigation, ships experience continuous shaking, tilting, and vibration, which impose extremely high requirements on the structural strength and reliability of the valves. They are installed on critical life-support systems, such as the ballast water system (directly affecting the ship's stability), the seawater cooling system (ensuring the operation of the main engine), the fire protection system (ensuring safety), and the fuel system. Once they fail, it may lead to serious mechanical failures or even safety accidents.
Water treatment butterfly valve:
Its core mission is to achieve reliable control and regulation of water flow in systems such as municipal water supply, sewage treatment, irrigation, and industrial circulating water. The environmental challenges it faces mainly stem from the water quality itself: fresh water, clean water, wastewater containing various chemical agents, slightly corrosive reclaimed water, or slurry containing particulate impurities. Although there are also issues of corrosion and wear, salt fog corrosion is not typically involved. The operating environment is relatively stable, with no continuous fluctuations or impacts.
II. Material Selection: Corrosion Resistance vs. Cost-Efficiency
This is the most obvious difference between the two, which is determined directly by their operating environment.
Marine butterfly valve:
The first priority in material selection is to achieve the highest resistance to seawater corrosion.
Valve body and butterfly plate: Bronze and naval brass are widely used. For larger or more demanding applications, duplex stainless steel (such as 2205, 2507, etc.) is adopted. These materials are expensive, but their excellent resistance to chloride stress corrosion and pitting corrosion are the foundation for ensuring long-term safe operation. Ordinary 304 stainless steel and even cast iron are strictly prohibited here because they will rapidly suffer from pitting and crevice corrosion in seawater.
Valve seat: Usually made of EPDM (terpolymer ethylene propylene diene monomer) or NBR (nitrile butadiene rubber), but the formulation will be optimized according to the characteristics of seawater.
Valve stem: It must be made of stainless steel or a higher-grade metal and undergo special surface treatment to ensure absolute reliability.
Water treatment butterfly valve:
When selecting materials, priority is given to economic efficiency and applicability while ensuring performance.
Valve body and butterfly plate: Ductile iron is the absolute mainstream material, due to its excellent strength and excellent cost control. To prevent rusting, the valve body is usually coated with epoxy resin or other anti-corrosion coatings. For the dosage process of highly corrosive agents, plastic valves such as PP (polypropylene) or PVC may be used; for water-cleaning scenarios, stainless steel (304 or 316) is also quite common.
Valve seat: The material selection is more diverse, depending on the medium: EPDM (used for clean water and sewage), NBR (used for oily media), PTFE (polytetrafluoroethylene, used for chemical agents), etc.
III. Design and Structural Characteristics: Robust and Reliable vs. Functional and Practical
Marine Butterfly Valve:
Structural strength: The design must be capable of withstanding the swaying and impacts of the ship, and the components are made sturdier, with more reliable connection structures.
Drive method: Considering the operating space and reliability, gearboxes are mostly used for operation (which is convenient for force-saving operation and precise adjustment), or hydraulic/ pneumatic actuators are adopted. The form of direct operation by handwheels is less common.
Fire prevention design: Valves installed in dangerous areas such as the fuel system must have a fire safety design. That is, in the event of a fire, even if the soft-sealing valve seat burns out, the metal valve seat can still maintain a certain degree of sealing to prevent fuel leakage from intensifying the fire.
Zero leakage requirement: For valves in critical systems, the sealing grade must be extremely high. Usually, it is required to achieve bidirectional zero leakage.
Water treatment butterfly valve:
Structural design: It is more inclined towards generalization and modularization to meet the requirements of large-scale procurement and installation.
Drive method: There are various forms. Manual lever type, manual worm gear type, electric, pneumatic, etc. are all very common. The choice depends on the size of the pipeline and the degree of automation.
Sealing grade: Although a good seal is required, except for some specific conditions, the requirement for "zero leakage" is usually not as strict as in the marine field.
