原文：
换向型方向控制阀(简称换向阀)，是通过改变气流通道而使气体流动方向发生变化，从而达到改变气动执行元件运动方向目的。它包括 气压控制换向阀、电磁控制换向阀、机械控制换向阀、人力控制换向阀和时间控制换向阀等。 １、气压控制换向阀 气压控制换向阀，是利用气体压力来使主阀芯运动而使气体改变流向的。按控制方式不同分为加压控制、卸压控制和差压控制三种。加压控制是指所加的控制信号压力是逐渐上升的．当气压增加到阀芯的动作压力时，主阀便换向；卸压控制是指所加的气控信号压力是减小的，当减小到某一压力值时，主阀换向；差压控制是使主阀芯在两端压力差的作用下换向。 气控换向阀按主阀结构不同，又可分为截止式和滑阀式两种主要形式。滑阀式气控换向阀的结构和工作原理与 液动换向阀基本相同。在此主要介绍截止式换向阀。 截止式换向阀的工作原理 当K口无信号时。A与T通、阀处于排气状态；当K口有信号输入后，压缩空气进入活塞9的有端，使阀杆5左移、P与A通。图中所示的为 常断型阀，如果P与T换接则成为常通型。 ２、先导式电磁换向阀 先导式电磁换向阀是由电磁铁首先控制气路，产生先导压力，再由先导压力去推动主阀阀芯，使其换向。适用于通径较大的场合。 它由先导阀(Dl、D2)和主阀组成。而主阀又包括阀体1和活塞组件2两部分。图示的是Dl、D2均处于断电的状态。电磁阀的动铁芯5、6处于关闭状态。当 Dl通电、D2断电时，动铁芯5被吸起，由P口来的压缩空气经孔a(虚线)进入阀的f腔。并从密封塞4(单向阀)的四周唇边进入孔‘，并进入。广腔，推动活塞组件2下移，使P与A通，B经阀芯中心孔h与T通(排气)。A口有压缩空气输出的同时，有一部分压缩空气流入孔g，其中一路经节流孔d进入c腔使密封塞4下移封住排气孔b，另一路压缩空气进入f腔，作用在活塞组件2的上端。此时，即使Dl断电， 活塞组件2也不会位即该阀具有记忆功能。 当先导阀D2通电、Dl断电时，动铁芯6被吸起，c腔内的压缩空气经T1口排出。此时从P到A的压缩空气作用在大、小活塞上，因大、小活塞的面积差而产生向上的作用力，使活塞组件2上移。与此同时，密封塞4也上移，并打开阀口3，使活塞组件2上端的压缩空气经孔6排掉。活塞组件2上移后，P与B通，A与T通(排气)。此时即使D2断电，因大小活塞面积差而产生向上的作用力依然存在，所以输出状态也不会改变，即具有记忆功能。气动电磁换向阀与液压电磁换向阀一样，有很多类型，其工作原理也相似，不再赘述。

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For the directional control valve (the valve), is by changing the flow direction of gas flow channel Ershi change in order to change the direction of pneumatic actuators campaign purposes. It includes the pressure control valve, solenoid control valve, mechanical control valve, control valve and the time control of human valve and so on. 1, pressure control valve Pressure control valve, gas pressure is used to make the main spool ideal brings change the flow of gas. Pressure under control were divided into control mode, three types of pressure relief control and differential control. Pressure control is added by the control signal pressure is gradually rising. When the air pressure to the pressure spool moves, the main valve will be changed to; pressure relief control means in the increase of gas pressure control signal is reduced, when reduced to a certain pressure value, the main valve commutation; difference pressure control is the main spool to the role of pressure difference at both ends under the commutation. Gas control valve according to the main valve structure is different, closing ceremony and slide can be divided into two main forms of valve. Slide valve gas control valve of the structure and working principle is basically the same with the hydraulic valve. This introduces the cut-off type valve. Cut-off type valve works When the K I no signal. A and T through the valve in the exhaust state; when K has signal input port, the compressed air into the piston 9, a side to make the stem 5, left, P and A pass. Shown in the figure for regular off-valve, if P and T for access is a regular pass type. 2 Pilot solenoid valve Pilot solenoid valve is controlled by a solenoid first gas line, resulting in the pilot pressure, the pressure by the pilot to push the main valve spool, to change to. Apply to the larger diameter occasions. It consists of the pilot valve (Dl, D2) and the main valve. The main valve also includes valve body 1 and piston 2 in two parts. Icon is Dl, D2 are in the power of the state. Moving core 5,6 solenoid valve is turned off. When the power Dl, D2 power, the moving core 5 from being sucked from the P port to the compressed air through holes a (dotted line) of f into the valve chamber. And from the sealing plug 4 (one-way valve) into the hole around the lips', and enter. Canton chamber, push the piston downward component 2, so P and A pass, B through the spool and the T h through the central hole (exhaust). A compressed air output port, while some compressed air into the hole g, by the way in which to enter c d orifice plug cavity to seal shut the exhaust port 4 Down b, f another way of compressed air into the chamber, acting on the piston Component 2 of the top. At this point, even if the Dl power, piston 2 will not place that has a memory function of the valve. When the pilot valve energized D2, Dl power, the moving core 6 is pick up, c T1 oral cavity of the compressed air through discharge. At this point the compressed air from P to A role of large and small piston, due to the large and small piston area difference caused by upward force, so that piston assembly 2 upward. At the same time, sealing plug 4 is also on the move, and open the valve port 3, so that the top of the air piston assembly 2 is drained by the holes 6. After the piston 2 on the move, P and B pass, A and T through (exhaust). At this point even if the D2 power, because of the size difference caused by the piston area is still up in force, it will not change the output state, which has a memory function. Pneumatic and hydraulic solenoid valve solenoid valve, as there are many types, it works similar, not repeat them.

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