Some solenoid valves are designed in such a way that the direction of fluid flow through them is irrelevant. Thus, we see that the label “2-way” does not refer to two directions of flow as one might assume, but rather two ports on the valve for fluid to travel through. Otherwise (below note point), enough fluid pressure might override the return spring’s action, preventing the valve from achieving its “normal” state when de-energized. Process fluid pressure should be applied to the valve in such a way that the pressure difference tends to hold the solenoid valve in its “normal” position (the same position as driven by the return spring). Most solenoid valves use a “globe” or “poppet” style of valve element, where a metal plug covers up a hole (called the “seat”).
The arrow inside a solenoid valve symbol actually denotes a preferred direction of flow. Unlike electrical switches, of course, the terms open and closed have opposite meanings for valves.Īn “open” electrical switch constitutes a break in the circuit, ensuring no current an “open” valve, by contrast, freely allows fluid flow through it.Ī “closed” electrical switch has continuity, allowing current through it a “closed” valve, on the other hand, shuts off fluid flow. In a fluid control schematic, it is left to the reader to visualize the valve symbol boxes moving to and fro, determining the flow path of fluid through the valve. This sort of coloring and re-positioning is never shown in a real schematic diagram. What you see in the above illustration are “dramatized” symbols, highlighting the valve’s action by color and by re-positioning the boxes, strictly for the purpose of making it easier for you to grasp the concept. As with electrical switches in schematic diagrams, fluid control valve symbols are always drawn in their “normal” (resting) states.įor example, a normally-closed valve will always be drawn so that the box with the blocked ports aligns with the tubes leading to and from the valve.
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