Control valves used in pneumatic and hydraulic fluid power systems often take the form of a spool mechanism, and the fluid power schematic symbols for these spool valves are quite unlike that of valve symbols in P&IDs and loop diagrams:
Explain what these spool valve symbols represent, and how they are to be interpreted. Also, comment on the construction of a spool valve.
The symbols show each valve’s “normal” (unactuated) position. To understand what happens when the valve is actuated, you must visualize the boxes sliding over into alignment with the inlet/outlet pipes, like this:
The same holds for the reversing valve, except that it has three positions:
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Credits: Tony R. Kuphaldt