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气动活塞直通二位切断阀（以下简称气动切断阀）是生产过程自动化中采用的终端控制机构，它根据控制的工作信号执行指令，改变进入工艺过程的介质流量、压力、温度和液位等参数的调节。
气动切断阀具有结构简单、动作敏捷、安全可靠、维修方便及防爆等优点，广泛应用石油、化工、电力、轻纺、医药、造纸等工业生产过程的自动化调节和远程控制中。
2、结构及作用原理
气动切断阀由活塞执行机构和切断阀两部分组成。主要有缸盖、弹簧、活塞、缸套、推杆、阀瓣、阀座、阀体、密封填料等零件组成。
当输入信号压力通过管接头输入气缸室在活塞上产生推力，使活塞产生位移并压缩弹簧。活塞的位移带动推杆，阀杆和阀瓣作相应的位移，使切断阀达到额定的行程值。
按作用方式不同可分为气关式和气开式两种，当信号压力增加推杆向上移动，使阀瓣与阀座离开都为气开式，该阀型为反作用气开式执行机构。
本气动切断阀结构新颖，阀体内的流路涡流阻力小，因而提高了阀的流量系数。阀瓣密封面采用石墨聚四氟乙烯柔性密封填料，密封性能可靠，阀的动作由反作用气开执行机构驱动，使阀的结构紧凑，性能稳定良好，还可手动旋转气缸顶部的手轮来调节阀瓣的行程，以适应不同工艺的流量控制，可替代同类型的二位式薄膜切断阀。
1、Purpose
Pneumatic piston straight-through two-position shut-off valve (hereinafter referred to as pneumatic shut-off valve) is a terminal control mechanism used in the production process automation, based on the controlled work signal, which executes instructions, change and adjust the medium flow, pressure, temperature and level and other parameters into the process.
Pneumatic shut-off valve has advantage of simple structure, agile operation, safety and reliability, easy maintenance and anti-explosion, etc., widely used in automate regulation and remote control in industrial process of petroleum, chemical, power, textile, pharmaceutical, papermaking and other.
2、the structure and principle
Pneumatic shut-off valve is composed of two parts: the piston actuator and the shut-off valve, mainly including cylinder head, spring, piston, cylinder liner, push rod, valve clack, valve seats, valve body, sealing filler and other parts.
When the input signal pressure is input into the cylinder chamber through the pipe joint, and thrust is generated on the piston, which makes the displacement of the piston and the compression of spring. The displacement of piston drives the displacement of the push rod, valve rod and valve clack accordingly, making the shut-off valve reach the rated travel value.
According to the mode of action, it can be divided into two types: air-to-close and air-to-open. When the signal pressure increases and the push rod moves upward, the valve clack leaves valve seat, which is air-to-open. This type of valve is the reaction air-to-open actuator.
The pneumatic shut-off valve has novel structure, small eddy resistance of flow path in the valve body, thus increasing the discharge coefficient of the valve. The sealing surface of valve uses graphite PTFE soft sealing packing, thus sealing performance is reliable, and the action of the valve is driven by the reaction air-to-open actuator, so the valve structure is compact, and has stable performance. Meanwhile, the adjustment of the valve clack travel can be achieved by rotating manually hand wheel on the top of the cylinder to accommodate flow control of different technologies. It can replace the same type of two-position thin-film shut-off valve.
