It's worth taking some time to become familiar with this class of directional control valve (DCV) because they are incredibly common for handling 100+ GPM (400+ LPM) flows. You'll encounter them in both plant and mobile settings; they are a go-to valve used in all kinds of different hydraulics applications.
We've been referring to this valve as a DCV, which is a shortened way of saying directional control valve.
Because pilot operated DCVs are so common, you'll hear different people refer to them by different names. A couple of popular names are 2-Stage Valves, and Master-Slave valves.
The average solenoid-controlled, pilot operated DCV has two or three sections plumbed together as a valve stack.
The main valve section is what it's all about. This is the section that does the work of directing flow out to the system components. It often handles high pressures and large volumes of fluid, so it will be the physically largest part of the valve stack. (This is the section that would be the "slave" section, if you are referring to the valve as master-slave).
A very common spool and port arrangement is a four port, three position closed center valve, as shown here. (The manifold block is drawn in as well.)
Float center spools are also very popular. When de-energized, the spool connects the A and B lines to the tank.
Use the controls to send the main spool back and forth. A graphic cutaway of a closed center valve is on the left, and its schematic is on the right.
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