The solenoid valve symbol on an electrical schematic depends entirely on the drafting standard used by the engineer. In North America, you will typically see NEMA/JIC (National Electrical Manufacturers Association / Joint Industry Council) symbols, while the rest of the world relies on IEC 60617 (electrical) and ISO 1219 (fluid power) standards. At its core, every standard represents the valve as two distinct elements: the fluid body (ports and flow paths) and the electrical actuator (the coil).

The Complete Solenoid Valve Symbol Reference Table

Use this matrix to decode the most common valve configurations you will encounter on machine prints. The fluid power side (ISO 1219) defines the squares and arrows, while the electrical side (IEC/NEMA) defines the coil symbol attached to the end of the valve body.

Valve Type ISO 1219 / IEC 60617 Symbol Description NEMA / JIC Symbol Description Practical Application & Meaning
2/2-Way NC Two squares (positions), two port lines. Spring return symbol on one end, solenoid rectangle with diagonal line on the other. Two squares, two ports. Solenoid coil shown as a loop or rectangle with 'SOL' inside, opposed by a zigzag spring. Normally Closed. Blocks flow when de-energized. Used for basic on/off fluid control (e.g., draining a tank).
2/2-Way NO Two squares, two port lines. The 'normal' (unactuated) square shows flow paths aligned with the ports. Similar to NC, but the flow path arrows in the resting state square align directly with the port lines. Normally Open. Allows flow when de-energized. Used for cooling lines or fail-safe venting.
3/2-Way Two squares (positions), three port lines (Pressure, Work, Exhaust). Two squares, three ports. Often drawn with a single solenoid and a spring return. Controls a single-acting pneumatic cylinder. Energizing shifts flow to the cylinder; de-energizing vents it to exhaust.
5/2-Way Two squares, five port lines. Often features two solenoids (one on each end) or one solenoid with a spring. Two squares, five ports. Double-solenoid versions show two 'SOL' rectangles on opposite ends. Controls a double-acting pneumatic cylinder. Directs air to extend or retract the piston rod.
Proportional Standard valve squares, but the solenoid symbol includes a diagonal arrow through the coil rectangle. Rectangle with 'PROP' or an internal arrow indicating variable current control. Infinitely variable flow control. Requires a 4-20mA or 0-10VDC analog signal, not simple discrete on/off.

Regional Standards and the 'Rows People Get Wrong'

Reading a schematic from a machine imported from Germany versus one built in Ohio requires a mental gear shift. The Womack Machine fluid power symbol library is an excellent cross-reference for US-based technicians dealing with ISO prints.

Which Standard Applies to Your Region?

  • IEC 60617 / ISO 1219 (Global/Europe/Asia): The international standard. Electrical coils are rectangles with a diagonal line. Valve bodies are adjacent squares representing discrete states.
  • NEMA / JIC (North America): Dominates US industrial control panels. Electrical coils are often drawn as a circle with 'CR' (Control Relay) or 'SOL' inside, or a specific loop shape. Note: The NEC (National Electrical Code) governs wiring methods and wire colors, but it does not dictate schematic symbols.
  • BS 3939 (Old UK): Withdrawn in favor of IEC, but you will still see it on legacy British machinery. It used hybrid symbols that look remarkably like old relay coils with mechanical linkages drawn explicitly.

The Rows People Get Wrong

Even experienced technicians misread specific symbol variations. Watch out for these common traps:

  • The Manual Override: In ISO 1219, a manual override looks like a small button or a zigzag line attached to the solenoid square. Technicians frequently confuse the diagonal line of the IEC solenoid coil itself with a manual override indicator. If the diagonal line is inside the electrical rectangle, it is just the coil.
  • Detented (Latching) vs. Spring Return: A 5/2-way valve with two solenoids and no spring symbols is detented. It stays in its last shifted position when power is removed. If you assume it springs back to center, your machine will crash on the next cycle.
  • 3/2-Way vs 2/2-Way: Count the port lines intersecting the main square. Three lines mean it has an exhaust port. If you cap the exhaust port thinking it is a simple 2-way shutoff valve, the downstream actuator will become hydraulically locked.

Safe Interpretation When Markings Are Faded or Missing

WARNING: Never guess a valve's fail-state based on a faded, oil-stained, or partially torn schematic. Assuming a valve is Normally Closed when it is actually Normally Open can result in unexpected pneumatic cylinder movement or fluid release when the machine is locked out for maintenance.

When the print is illegible, or the physical valve label has been destroyed by washdown chemicals, you must verify the valve's behavior electrically and physically.

1. Verify the Coil Electrical Characteristics
Disconnect the wiring and use a multimeter to measure the coil resistance. This tells you the voltage rating, which dictates your control circuit design:

  • 24VDC Coils: (e.g., SMC SY3000 series or Festo VUVG) typically read between 15 Ω and 45 Ω. If you measure this, ensure your PLC output has a flyback diode across the coil to prevent voltage spikes from frying the solid-state output.
  • 120VAC Coils: (e.g., ASCO 8210 series) typically read between 100 Ω and 400 Ω.
  • Open Line (OL): If the meter reads infinite resistance, the internal thermal fuse or the copper winding is burned out. The valve is electrically dead, regardless of what the schematic says.

2. Identify the DIN Connector Pinout
Most industrial solenoids use a DIN 43650 connector. If the wiring is ripped out:

  • Form A (Large): Pin 1 is Line/+, Pin 2 is Neutral/-, Pin 3 (or Ground screw) is Earth. Often includes an internal LED and varistor.
  • Form B / C (Micro): Pin 1 is Line/+, Pin 2 is Neutral/-. Pin spacing is tighter (8mm or 9.4mm). Do not force a Form A plug into a Form B valve; you will short the control board.

3. The Physical 'Push' Test
Locate the manual override button on the valve body (usually a small recessed cylinder requiring a 2mm Allen key or a small flathead screwdriver). With the air supply on and the machine in a safe, unclamped state, press the override. If the cylinder extends, you have mapped the 'energized' state. Release it. If it retracts, it is spring-return. If it stays extended, it is a detented/latching valve.

Solenoid Valve Schematic FAQs

What does the diagonal line through a solenoid valve symbol mean?

In an IEC 60617 electrical schematic, a rectangle with a diagonal line through it is the universal symbol for an inductive coil (the solenoid). However, in an ISO 1219 fluid power schematic, a diagonal arrow crossing the solenoid box indicates a proportional or variable-force solenoid, meaning it requires an analog current signal (like 4-20mA) rather than a simple digital 24VDC on/off signal. Always check the title block of the drawing to confirm if you are looking at the electrical control print or the pneumatic/hydraulic fluid print.

How do I wire a 3-way vs 2-way solenoid valve based on the schematic?

The electrical wiring to the coil is exactly the same for both. A 2/2-way and a 3/2-way solenoid valve both typically use a standard 2-pin DIN connector (plus ground). You wire your PLC output or relay contact to Pin 1, and your DC common/AC neutral to Pin 2. The '3-way' designation refers strictly to the fluid ports (Pressure, Work, Exhaust) on the brass or aluminum body, not the electrical wires. The schematic will show this difference by drawing three fluid lines intersecting the valve's state squares instead of two.

Why does my schematic show two solenoid coils on one valve body?

This indicates a double-solenoid valve, typically a 5/2-way or 5/3-way configuration used to control double-acting pneumatic cylinders. It requires two separate electrical control wires from your PLC or relay logic. In a 5/2-way detented valve, pulsing Coil A shifts the valve, and it stays there even after Coil A is turned off, until Coil B is pulsed. In a 5/3-way valve, energizing Coil A shifts it one way, Coil B shifts it the other, and when both coils are de-energized, internal springs center the valve to block all airflow or vent it to exhaust, depending on the center-block configuration shown in the middle square of the ISO symbol.