Pneumatic Systems
// Visual symbol reference — how to read pneumatic circuit diagrams
// Directional Control Valve Symbols
2/2 NC Valve
Normally Closed. Solenoid opens it, spring closes it. 2 ports, 2 positions.
2/2 NO Valve
Normally Open. Solenoid closes it, spring reopens. Fail state = open.
3/2 Valve
3 ports (P, A, R), 2 positions. Routes supply or vents output. Used on fill valves.
5/2 Valve
5 ports, 2 positions. Controls double-acting cylinders. Numatics type on your plant.
Spring-Return Actuator
One air port. Air extends piston, spring retracts it. Fail-safe = retracted.
Double-Acting Actuator
Two air ports (A, B). Air in A extends, air in B retracts. Used on drop valves.
Pressure Regulator
Reduces and stabilizes downstream air pressure. Adjustable set point.
Filter / FRL Unit
Filter-Regulator-Lubricator. Cleans and conditions air before solenoid valves.
// Port Label Reference
| Label | Full Name | Function | Typical Connection |
|---|---|---|---|
| P | Pressure / Supply | Always pressurized air inlet | From FRL or regulator |
| A | Output A | First working port — extends or opens | Cylinder cap end |
| B | Output B | Second working port — retracts or closes | Cylinder rod end |
| EA / R | Exhaust A | Vents port A side to atmosphere | Open air or muffler |
| EB / S | Exhaust B | Vents port B side to atmosphere | Open air or muffler |
| X / Y | Pilot Signal | External pilot air to shift spool remotely | From pilot solenoid |
// How to Read a Pneumatic Circuit
Valve Notation — X/Y
First number = ports (air connections)
Second number = positions (states)
3/2 = 3 ports, 2 positions
5/2 = 5 ports, 2 positions
5/3 = 5 ports, 3 positions (center off)
Second number = positions (states)
3/2 = 3 ports, 2 positions
5/2 = 5 ports, 2 positions
5/3 = 5 ports, 3 positions (center off)
Box Symbols
Each box = one valve position
Solid border = normal/de-energized state
Dashed border = energized/shifted state
Arrows inside = flow direction.
Dead ends = blocked ports.
Solid border = normal/de-energized state
Dashed border = energized/shifted state
Arrows inside = flow direction.
Dead ends = blocked ports.
Actuator Symbols
Spring zig-zag = spring-return (fail-safe)
Two ports, no spring = double-acting
Square box with S = solenoid actuator
Spring side defines the fail-safe position when de-energized.
Two ports, no spring = double-acting
Square box with S = solenoid actuator
Spring side defines the fail-safe position when de-energized.
Dextrose Plant — What You'll See
Fill valves: 3/2 spring-return (fail closed)
Drop valves: 5/2 double solenoid (no spring)
Divert valves: 3/2 with pilot
Crystallizer solenoids: 120VAC, 1500–3000Ω coil
Drop valves: 5/2 double solenoid (no spring)
Divert valves: 3/2 with pilot
Crystallizer solenoids: 120VAC, 1500–3000Ω coil
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