How schematic symbols for control valves is derived?
Let’s consider a 3 position 4 port valve.
Control valves are represented using square boxes. Each square boxes represent positions. the number of boxes in the figure specifies the number of operating positions, for example, 3 boxes represent 3 positions.
Pipeworks are normally represented in connection with the box which represents unoperated conditions. As shown in the above figure the position 2 is in unoperated condition. Hydraulic circuits are normally operated in unoperated condition.
In the above figure, all positions have 4 ports each. The position 2 has all ports blocked. the arrow marks in the position1 and position 3 show the direction of flow. So this is 3 position 4 port valve. this is how the name of the control valve is derived.
How this valve operate?
There is no flow at the current position that means at the position 2 all ports are in blocked condition as shown in the figure below. Thus it is getting pressurized.
When the position 1 aligns with the pipe
When the position 1 aligns with the pipe as in the figure below, the flow is happening in both directions since the pipe is connected.
When position 3 aligns with the pipe
When position 3 aligns with the pipe will be as shown in the figure below. the flow is getting reversed. That’s how it works.