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The first "installment" was drawing a 2/2 valve.
Here's how to draw the 3/2 compressed air valve.
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Start by drawing a square on your paper, a couple of inches square. You will find it easier if you use graph paper to help keep the lines straight.
After you've drawn your box, add three lines inside the square as shown in Fig. 21. The black outer square box depicts the valve body. The three little lines inside the square box show where the internal air passages and the external air ports are.
There are three compressed air ports in a 3/2 valve. The number of ports in a valve is indicated by the first number of a specific valve’s designation, and as always, the second number in that designation indicates the number of positions that particular valve will have. This is a 3/2 valve, so it will have three air ports, and two valve positions.
You can’t tell from the outside how many positions a valve will have. The positions of the valve are selected by shifting the internal flow paths of a particular valve via a valve actuator.
Did I mention that you'll want to do your drawing in pencil, and have an eraser handy too, hmmmm? Until you get familiar with the process, I can almost guarantee that you’ll do a lot of erasing and changing of the lines.
Some circuit designers show the lines that are depicting the ports extending slightly through the wall of the valve when drawing their valve schematics. Some don't. I am of the latter persuasion.
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Fig. 22 shows the same box, but now we've connected up two of the ports, and modified the other one slightly.
The black circle signifies the compressed air supply. It is flowing from the circle up to and into the 3/2 valve. This is a simple way to show that this valve is connected to an air supply, which is connected to the plant air mains, which are, in turn, connected to the compressor. A lot of meaning in a small black circle, hmmm?
Compressed air cannot pass through the valve in Fig. 22 because the supply port inside the valve is closed. That’s indicated by the small line “teeing” the top of the line coming from the air supply.
If this 3/2 valve was at rest, that is to say that there are no external valve actuators affecting the valve position, then it would be an NC (normally closed) air valve.
Note the line drawn from the top of the box to the bottom left, and that the line has an arrow head. This shows the open flow path of the air through this valve when it is in this position. It is open from the top port, through the valve, and out the bottom port where the arrow head is located.
You will, of course, have erased the small vertical lines that I told you to draw in Fig. 21, by now?
In Fig. 22 the port that is blocked or closed is the supply port. The port at the top of the box is the actuator or application port that is connected by an air line to the end application ( a tool, actuator etc) and the port that has the arrowhead pointing to it is the exhaust port.
With the valve shifted into the position shown in Fig. 22, or if this is the at rest position for this valve, the supply is shut off and the actuator port is opened to exhaust which allows the compressed air to exhaust to atmosphere.
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Fig. 23 shows the same valve, but now in it's shifted or alternate position. With the valve in this position, the supply air is moving through the valve to an application somewhere, and the other port, the exhaust port, is now closed.
The air will flow through the valve to an application, and the air will stay in that application until this valve is shifted back, and then the flow path will be as shown in Fig. 22 again.
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Fig. 24 takes the two drawings that we've made - Fig. 22 and Fig. 23, and places them side by side. This is a complete drawing for the flow paths of one 3/2 valve. The 3/2 valve has 2 positions, each position depicted by the drawing on one side or the other of the single valve schematic.
The way Fig. 24 depicts the valve, with the supply air coming into and through the valve, shows that when the valve is shifted to this position, then it's open.
If the positions are reversed, as shown in Fig. 25 just below, then the valve is closed.
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It is customary to draw a valve in the position that it will be at rest, when the valve in not being acted upon by an exterior actuator, or when the air circuit that the valve is part of, has stopped functioning.
Without the actuators being shown in the above schematics, a viewer cannot tell where this valve should be when it is at rest. In that case the supply circle is drawn on the right side of the valve schematic.
Sometimes when an air circuit stops functioning, one or some of the valves may be left in an actuated position. The supply line may be on the left in these circumstances. The circuit schematic will show the details if that is the case.
You will need valve actuators to complete this 3/2 valve schematic. Here's how to draw them.
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