Solenoid-Controlled, Pilot-Operated Directional Control Valves
Objectives
- Explain the function of a solenoid-controlled, pilot-operated directional control valve.
- Different spool types/porting arrangements.
- Internal and external piloting.
- Interpret the simplified and detailed schematic symbols.
- Explain the purpose of the optional pilot choke valve section.
What's so Special About These Valves?
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.
Solenoid controlled, pilot operated DCVs in a plant setting, shown in color.
Vocabulary
DCV
We've been referring to this valve as a DCV, which is a shortened way of saying directional control valve.
Other Names
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.
Basic Parts
The average solenoid-controlled, pilot-operated DCV has two or three sections plumbed together as a valve stack.
Main Valve Section
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).
Closed Center
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.)
Moving the valve spool to the left connects P to B, and A to T.
When the spool is centered, all ports are blocked.
Moving the valve spool to the right connects P to A, and B to T.
Float Center
Float center spools are also very popular. When de-energized, the spool connects the A and B lines to the tank.
Moving the spool to the left connects P to B, and A to T.
At center, P is blocked, and A and B connect to T.
Moving the spool to the right connects P to A, and B to T.
Try it!
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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