Classification by function and purpose

（一）关断阀这类阀门是起开闭作用的。常设于冷、热源进、出口，设备进、出口，管路分支线（包括立管）上，也可用作放水阀和放气阀。常见的关断阀有闸阀、截止阀、球阀和蝶阀等。闸阀可分为明杆和暗杆、单闸板与双闸板、楔形闸板与平行闸板等。闸阀关闭严密性不好，大直径闸阀开启困难；沿水流方向阀体尺寸小，流动阻力小，闸阀公称直径跨度大。截止阀按介质流向分直通式、直角式和直流式三种，有明杆和暗杆之分。截止阀的关闭严密性较闸阀好，阀体长，流动阻力大，公称直径为DN200。球阀的阀芯为开孔的圆球。板动阀杆使球体开孔正对管道轴线时为全开，转90°为全闭。球阀有一定的调节性能，关闭较严密。蝶阀的阀芯为圆形阀板，它可沿垂直管道轴线的立轴转动。当阀板平面与管子轴线一致时，为全开；闸板平面与管子轴线垂直时，为全闭。蝶阀阀体长度小，流动阻力小，比闸阀和截止阀高。

（1） Shut off valve this kind of valve is used for opening and closing. It is always used at the inlet and outlet of cold and heat sources, the inlet and outlet of equipment, and the branch line of pipeline (including riser). It can also be used as drain valve and vent valve. Common shut-off valves include gate valve, globe valve, ball valve and butterfly valve. Gate valves can be divided into rising stem and Non rising stem, single gate and double gate, wedge gate and parallel gate, etc. The closing tightness of the gate valve is not good, and it is difficult to open the large-diameter gate valve; Along the direction of water flow, the valve body has small size, small flow resistance and large nominal diameter span of gate valve. According to the medium flow direction, the stop valve is divided into straight through type, right angle type and direct flow type, which can be divided into exposed rod and concealed rod. The closing tightness of the stop valve is better than that of the gate valve. The valve body is long and the flow resistance is large. The nominal diameter is DN200. The valve core of the ball valve is a round ball with an opening. Move the valve rod to make the opening of the ball face the axis of the pipe, which is fully open, and turn 90 ° to fully close. The ball valve has certain regulation performance and is tightly closed. The valve core of the butterfly valve is a circular valve plate, which can rotate along the vertical axis perpendicular to the pipeline axis. When the plane of the valve plate is consistent with the axis of the pipe, it is fully open; When the plane of the ram is perpendicular to the pipe axis, it is fully closed. Butterfly valve body length is small, the flow resistance is small, and the price is higher than that of gate valve and stop valve.

（二）止回阀这类阀门用于防止介质倒流，利用流体自身的动能自行开启，反向流动时自动关闭。常设于水泵的出口、疏水器出口以及其他不允许流体反向流动的地方。止回阀分旋启式、升降式和对夹式三种。对于旋启式止回阀，流体只能从左向右流动时，反向流动时自动关闭。对于升降式止回阀，流体从左向右流动时，阀芯抬起，形成通路，反向流动时阀芯被压紧到阀座上而被关闭。对于对夹式止回阀，流体从左向右流动时，阀芯被开启，形成通路，反向流动时阀芯被压紧到阀座上而被关闭，对夹式止回阀可多位安装、体积小、重量轻、结构紧凑。

（2） Check valve this kind of valve is used to prevent the medium from backflow, open it by using the kinetic energy of the fluid itself, and close it automatically in case of reverse flow. Standing at the outlet of the water pump, the outlet of the steam trap and other places where the reverse flow of fluid is not allowed. Check valves are divided into swing type, lifting type and wafer type. For swing check valves, the fluid can only flow from left to right, and automatically closes in reverse flow. For the lift check valve, when the fluid flows from left to right, the valve core is lifted to form a path. When the fluid flows in the opposite direction, the valve core is pressed onto the valve seat and closed. For the wafer check valve, when the fluid flows from left to right, the valve core is opened to form a path. When the fluid flows in the opposite direction, the valve core is pressed onto the valve seat and closed. The wafer check valve can be installed in multiple positions, with small volume, light weight and compact structure.

（三）调节阀阀门前后压差一定，普通阀门的开度在较大范围内变化时，其流量变化不大，而到某一开度时，流量急剧变化，即调节性能不佳。调节阀可以按照信号的方向和大小，改变阀芯行程来改变阀门的阻力数，从而达到调节流量目的的阀门。调节阀分手动调节阀和自动调节阀，而手动或自动调节阀又分许多种类，其调节性能也是不同的。自动调节阀有自力式流量调节阀和自力式压差调节阀等。

（3） The pressure difference between the front and back of the regulating valve is certain. When the opening of the ordinary valve changes in a large range, the flow changes little, while when it reaches a certain opening, the flow changes sharply, that is, the regulation performance is poor. The regulating valve can change the resistance number of the valve by changing the spool stroke according to the direction and size of the signal, so as to achieve the purpose of regulating the flow. The regulating valve is divided into manual regulating valve and automatic regulating valve, and the manual or automatic regulating valve is divided into many kinds, and its regulating performance is also different. Automatic regulating valves include self operated flow regulating valve and self operated differential pressure regulating valve.

（四）真空类真空类包括真空球阀、真空挡板阀、真空充气阀、气动真空阀等。其作用是在真空系统中，用来改变气流方向，调节气流量大小，切断或接通管路的真空系统元件称为真空阀门。

（4） Vacuum class vacuum class includes vacuum ball valve, vacuum baffle valve, vacuum charging valve, pneumatic vacuum valve, etc. Its function is to change the air flow direction, adjust the air flow, and cut off or connect the pipeline in the vacuum system, which is called vacuum valve.

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