止回閥，是一種自動閥門，僅允許流體（液體、氣體）向一個方向流動，并能自動防止介質倒流。其核心原理是依靠介質自身的流動和壓力來開啟或關閉閥門，無需任何外部操作機構。

　　Check valve is an automatic valve that only allows fluid (liquid, gas) to flow in one direction and can automatically prevent medium backflow. The core principle is to rely on the flow and pressure of the medium itself to open or close the valve, without the need for any external operating mechanism.

　　一、核心結構與通用組件

　　1、 Core structure and common components

　　盡管種類繁多，但大多數止回閥都包含以下幾個基本部件：閥體?：閥門的主要外殼，用于連接管道，承受管道壓力。是流體通過的通道。閥瓣 ?或 關閉件：這是止回閥的核心運動部件。其名稱和形狀因類型而異（如圓盤、球體、兩片瓣葉等）。它是直接阻止介質倒流的關鍵零件。閥座?：閥瓣閉合時與之緊密接觸的密封面。閥座與閥瓣的配合質量決定了閥門的密封性能和內漏等級。輔助部件：根據類型不同，可能包括：彈簧?：提供額外的閉合力，幫助閥門快速關閉，防止水錘，并支持閥門在任意方向（水平、垂直向上、垂直向下）安裝。搖臂與 樞軸?：用于旋啟式止回閥，使閥瓣能像門一樣擺動。球導向架?：用于球式止回閥，限制球的運動軌跡。

　　Although there are many types, most check valves include the following basic components: valve body: the main housing of the valve, used to connect pipelines and withstand pipeline pressure. It is a channel through which fluids pass. Valve disc or closure: This is the core moving component of a check valve. Its name and shape vary depending on the type (such as disc, sphere, two lobes, etc.). It is a key component that directly prevents the backflow of the medium. Valve seat: The sealing surface that tightly contacts the valve disc when it is closed. The quality of the fit between the valve seat and the valve disc determines the sealing performance and internal leakage level of the valve. Auxiliary components: Depending on the type, they may include: springs: providing additional closing force to help the valve close quickly, prevent water hammer, and support valve installation in any direction (horizontal, vertical up, vertical down). Swing arm and pivot: used for swing check valves, allowing the valve disc to swing like a door. Ball guide frame: used for ball check valves to restrict the movement trajectory of the ball.

　　二、主要結構類型（基于閥瓣運動方式）

　　2、 Main structural types (based on valve disc movement mode)

　　這是最基礎也是最常見的分類方式，根據閥瓣如何運動來開啟和關閉。1. 旋啟式止回閥

　　This is the most basic and common classification method, which opens and closes based on how the valve disc moves. 1. Swing check valve

　　結構：閥瓣像一個鉸鏈門，通過搖臂和樞軸連接在閥體頂部。閥瓣可以自由擺動。工作原理：流體正向流動時，壓力將閥瓣推起；流動停止或反向時，閥瓣靠自重和回流壓力關閉。特點：流阻小，壓降低，適用于大流量、低流速的工況（如水泵出水口）。不適合流量頻繁變化的場合，關閉時易產生水錘，通常要求安裝在水平管道上。

　　Structure: The valve disc is like a hinged door, connected to the top of the valve body through a rocker arm and pivot. The valve disc can swing freely. Working principle: When the fluid flows forward, pressure pushes the valve disc up; When the flow stops or reverses, the valve disc closes by its own weight and reflux pressure. Features: Low flow resistance, reduced pressure, suitable for high flow and low flow conditions (such as water pump outlet). Not suitable for situations with frequent changes in flow, it is prone to water hammer when closed, and is usually required to be installed on a horizontal pipeline.

　　2. 升降式止回閥

　　2. Lift check valve

　　結構：閥瓣像一個活塞，通常帶有導向機構，沿閥座通道軸線做垂直升降運動。其結構與截止閥非常相似。工作原理：流體壓力頂起閥瓣；壓力下降時，閥瓣靠自重落回閥座。特點：密封性能優于旋啟式，但流阻較大。適用于高壓、小口徑場合（如鍋爐給水系統、高壓管道）。通常要求安裝在水平管道上。

　　Structure: The valve disc is like a piston, usually equipped with a guiding mechanism, and moves vertically up and down along the axis of the valve seat channel. Its structure is very similar to a globe valve. Working principle: Fluid pressure lifts the valve disc; When the pressure drops, the valve disc falls back to the valve seat by self weight. Features: The sealing performance is better than that of the rotary opening type, but the flow resistance is relatively high. Suitable for high-pressure and small-diameter applications (such as boiler feedwater systems and high-pressure pipelines). It is usually required to be installed on a horizontal pipeline.

　　3. 球式止回閥

　　3. Ball check valve

　　結構：用一個球體作為閥瓣。閥體內部通常有一個錐形閥座來容納球體。工作原理：流體壓力頂起球體；反向流動時，球體滾回錐形閥座并密封。特點：結構簡單，密封可靠，適用于高粘度、帶懸浮顆粒的介質（如泥漿、造紙漿液）。但噪音和水錘現象可能較明顯。

　　Structure: Use a sphere as the valve disc. There is usually a conical valve seat inside the valve body to accommodate the ball. Working principle: Fluid pressure lifts the sphere; When flowing in reverse, the sphere rolls back to the conical valve seat and seals. Features: Simple structure, reliable sealing, suitable for media with high viscosity and suspended particles (such as mud and paper pulp). But noise and water hammer phenomena may be more pronounced.

　　4. 瓣式（對夾式）止回閥

　　4. Flap type (clamp type) check valve

　　結構：由兩個半圓形的彈簧加載瓣片和一個中央銷軸組成。結構非常緊湊，重量輕。工作原理：流體壓力推開兩個瓣片；流動停止時，彈簧力和回流壓力迅速將瓣片關閉。特點：啟閉速度快，能有效減小水錘壓力；體積小、重量輕、成本低。廣泛應用于石油、化工、水處理等行業的空間受限場合。

　　Structure: Composed of two semi-circular spring-loaded flaps and a central pin shaft. The structure is very compact and lightweight. Working principle: Fluid pressure pushes apart two flaps; When the flow stops, the spring force and reflux pressure quickly close the flap. Features: Fast opening and closing speed, effectively reducing water hammer pressure; Small size, light weight, and low cost. Widely used in space constrained environments in industries such as petroleum, chemical, and water treatment.

　　三、特殊類別與高性能類型

　　3、 Special categories and high-performance types

　　這些是為了滿足特定苛刻工況而設計的止回閥。

　　These are check valves designed to meet specific harsh operating conditions.

　　1. 軸流式止回閥

　　1. Axial flow check valve

　　特點：閥瓣的開啟和關閉沿管道軸線方向運動，流道呈直線型，極其通暢。優勢：流阻極低，壓降非常小。開啟和關閉平穩迅速，水錘效應極低。應用：對壓力損失要求極高的場合，如長輸石油/天然氣管道、大型泵的出口、壓縮機系統。

　　Features: The opening and closing of the valve disc move along the axis of the pipeline, and the flow channel is linear and extremely smooth. Advantages: Extremely low flow resistance and very small pressure drop. Smooth and rapid opening and closing, with extremely low water hammer effect. Application: In situations where high pressure loss is required, such as long-distance oil/gas pipelines, large pump outlets, and compressor systems.

　　2. 緩閉式止回閥

　　2. Slow closing check valve

　　特點：帶有阻尼機構（如液壓油缸、彈簧和阻尼孔），可以控制閥瓣的關閉速度。優勢：主動防止水錘。它先快速關閉大部分行程（約80-90%）以防止倒流，最后一段行程緩慢關閉以消除壓力波動。應用：防止水錘危害至關重要的系統，如大型水泵站、電廠冷卻水系統、高層建筑給水系統。

　　Features: Equipped with damping mechanisms (such as hydraulic cylinders, springs, and damping holes), it can control the closing speed of the valve disc. Advantage: Proactively prevent water hammer. It first quickly closes most of the stroke (about 80-90%) to prevent backflow, and then slowly closes the last stroke to eliminate pressure fluctuations. Application: It is crucial to prevent water hammer hazards in systems such as large pump stations, power plant cooling water systems, and high-rise building water supply systems.

　　3. 截止止回閥

　　3. Cut off check valve

　　特點：它是截止閥和止回閥的結合體。它有一個額外的外部手輪或執行機構。優勢：具有兩種模式：止回模式：手輪完全抬起，閥瓣可自由活動，作為普通止回閥使用。截止模式：通過手輪強行將閥瓣壓緊在閥座上，充當截止閥，可以完全手動切斷流動。應用：鍋爐給水泵出口、汽輪機抽汽管路等需要雙重保障的關鍵場合。

　　Characteristic: It is a combination of a globe valve and a check valve. It has an additional external handwheel or actuator. Advantage: It has two modes: check mode: when the handwheel is fully raised, the valve disc can move freely and is used as a regular check valve. Cut off mode: By forcefully pressing the valve disc onto the valve seat with the handwheel, it acts as a shut-off valve and can completely manually cut off the flow. Application: Key occasions that require dual protection, such as the outlet of boiler feedwater pumps and the extraction pipelines of steam turbines.

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