"Pass" and "position" are important concepts of pneumatic directional solenoid valve. Different types of pneumatic directional solenoid valves are formed by different "on-off" and "position". Generally speaking, the "two position valve" and "three position valve" refer to that the spool of the reversing valve has two or three different working positions. The so-called "two-way valve", "three-way valve" and "four-way valve" refer to that there are two, three and four interfaces on the valve body of the directional valve which are not connected to each other and can be connected to different oil pipes or gas stations in the system. Different oil/gas channels can only be connected to the front "several positions" through the switch of the valve port when the valve core is shifted. You can say "several positions" depending on the working conditions of the valve. If there are symbols of pneumatic components, you can better understand, The number of the square representing the valve body (with arrows or T lines inside) on the symbol is several. The "several passes" in the back represents the number of points on one of the squares (the point where the arrow line and T line intersect), which is called "several passes".

The meanings of graphic symbols are generally as follows:

(1) A box is used to indicate the working position of the valve, and several boxes are used to indicate the number of "positions";

(2) The arrow in the box indicates that the oil circuit is connected, but the arrow direction does not necessarily indicate the actual direction of liquid flow;

(3) The symbol "-" or "field" in the box indicates that the access is blocked;

(4) The number of interfaces connected outside the box indicates the number of connections;

(5) Generally, the oil inlet/air inlet connecting the valve with the system oil supply circuit or air is indicated by the letter p; The oil/gas return port connected between the valve and the system oil/gas return circuit is represented by t (sometimes o); The oil port/air port connecting the valve and the actuating element is indicated by a, b, etc. Sometimes indicated by l on graphical symbols

(6) The reversing valve has two or more working positions, one of which is the normal position, that is, the position where the valve core is not subjected to longitudinal force. The middle position in the graphic symbol is the normal position of the three position valve. The two position valve that uses spring return takes the channel state in the box close to the spring as its normal position. Draw the system diagram. The oil/gas circuit is generally connected to the normal position of the reversing valve.