Solenoid Valve Symbol
Definition: The Solenoid Valve symbol represents an electrically operated fluid control valve drawn as a rectangle with a triangular flow indicator, two fluid-path terminals (In and Out) and two electrical coil terminals (Coil A and Coil B), denoting a device that opens or closes a fluid passage when its electromagnetic coil is energised, as referenced in ISO 1219-1 (pneumatic and hydraulic fluid power — graphical symbols) and ISO 10218 for industrial control schematics.
Also known as: electrically operated valve symbol, electro-pneumatic valve symbol, solenoid-operated valve, magnetic valve symbol, EV symbol.
What the Solenoid Valve symbol means
The Solenoid Valve symbol identifies a valve whose open/closed state is controlled by applying electrical current to a coil that generates a magnetic field, pulling or pushing a plunger to open or block the fluid path. In process and instrumentation diagrams (P&IDs) and pneumatic/hydraulic circuit diagrams, the symbol communicates that fluid flow between the In and Out ports is gated by an electrical control signal — typically from a PLC output, relay contact, or microcontroller — rather than by manual operation or mechanical actuation.
Solenoid valves are fundamental elements in automated fluid systems. The symbol appears in pneumatic motion circuits (controlling cylinders), hydraulic power units, water treatment dosing systems, HVAC refrigerant control, and fuel injection systems. When the coil is de-energised, a spring typically returns the valve to its default position (normally closed, NC, or normally open, NO), which must be documented in the schematic adjacent to the symbol.
How to identify the Solenoid Valve symbol
The Solenoid Valve symbol is a rectangle with a triangle pointing toward the right inside the box, indicating the allowable flow direction. Two horizontal fluid-path stubs exit the left and right sides of the rectangle (labeled In and Out), and two vertical stubs exit the top and bottom (labeled Coil A and Coil B) representing the electrical connections to the solenoid coil. The internal triangle pointing right indicates that flow direction is from In to Out when the valve is open. This differs from a manual gate valve symbol (diagonal line across the path) and a check valve symbol (triangle without enclosing box).
Function in a circuit
A solenoid valve uses electromagnetic force to actuate a valve mechanism. When current flows through the coil (Coil A to Coil B), the resulting magnetic field pulls a ferromagnetic plunger against a spring, either opening or closing the orifice between the In and Out ports depending on whether the valve is normally closed (NC) or normally open (NO). The coil typically draws 5–50 W at rated voltage (12 V DC, 24 V DC, 24 V AC, 110 V AC, or 230 V AC). Response times are typically 10–100 ms, making solenoid valves suitable for rapid automated control. Pilot-operated solenoid valves use a small solenoid to shift a pilot spool, which then uses process pressure to actuate the main valve, allowing large-bore valves to be controlled with low-power coils.
Standards: IEC vs ANSI
| IEC 60617 | ISO 1219-1 and ISO 1219-2 define graphical symbols for fluid power systems, including solenoid-operated valve symbols. IEC 60617 does not specifically cover solenoid valve symbols; ISA S5.1 (instrumentation symbols) and ISO 10628-2 cover P&ID symbol conventions for solenoid valves. The IEC/ISO symbol shows a square box (one valve position) with an electromagnet actuator box attached. |
|---|---|
| ANSI/IEEE 315 | ISA 5.1 (ANSI/ISA-5.1-2009, Instrumentation Symbols and Identification) is the primary North American standard for P&ID valve symbols. In ISA 5.1, a solenoid valve is shown as a globe valve symbol with 'SV' or 'EV' as the instrument tag. ANSI Y32.2/IEEE 315 does not specifically govern solenoid valve symbols. |
| Key difference | ISO 1219-1 (fluid power) uses a multi-position square symbol with flow-path arrows and an actuator box to show solenoid operation. ISA 5.1 (P&ID) uses a circle-and-valve body notation. The simplified rectangle with triangle used in electronics/electrical schematics is a block-level representation consistent with both conventions at the system diagram level. |
Terminals / pins
| Pin | Name |
|---|---|
| in | In |
| out | Out |
| coil_a | Coil A |
| coil_b | Coil B |
Typical values
Operating voltage: 12 V DC, 24 V DC, 24 V AC, 110 V AC, 230 V AC (typical). Coil power: 2–50 W. Operating pressure: 0–10 bar (low pressure), up to 350 bar (hydraulic). Flow rates: Cv 0.01 to over 100 depending on body size. Response time: 10–100 ms. Temperature range: −20°C to +80°C (standard), wider for specialty valves. Orifice sizes: 0.5 mm to over 50 mm.
Where the Solenoid Valve symbol is used
- Pneumatic automation systems where solenoid valves control air supply to cylinders and actuators based on PLC output signals
- Irrigation systems with solenoid valves on each zone, switched by a timer controller to distribute water on schedule
- HVAC refrigeration circuits using solenoid valves to isolate refrigerant flow to evaporator coils in multi-zone systems
- Water treatment dosing systems where solenoid valves meter chemical injection into process water
- Automotive fuel injection systems using miniature solenoid injectors pulsed by the engine control unit (ECU)
- Medical and laboratory equipment controlling fluid flow in analytical instruments, dialysis machines, and infusion pumps
- Gas appliances and burner control systems using safety solenoid valves (gas shut-off valves) with fail-closed spring return
Example
In a pneumatic pick-and-place robot schematic, a 5/2-way solenoid valve symbol (In and Out on the fluid path, Coil A and Coil B on the electrical path) controls a double-acting cylinder that moves a suction cup. A PLC output card supplies 24 V DC to Coil A to extend the cylinder (opening the valve to pressurize the cap end) and switches to Coil B to retract (redirecting air to the rod end). The symbol in the ladder logic diagram is cross-referenced to the pneumatic circuit diagram by a tag number.
Key facts
- The Solenoid Valve symbol represents an electrically operated fluid valve with two fluid terminals (In and Out) and two coil terminals (Coil A and Coil B), as defined in ISO 1219-1 and ISA 5.1.
- A solenoid valve opens or closes a fluid path when its coil is energised, using electromagnetic force to actuate a plunger; a spring returns the valve to its default (normally closed or normally open) state when the coil is de-energised.
- Common solenoid coil voltages are 12 V DC, 24 V DC, 24 V AC, 110 V AC, and 230 V AC; coil power consumption is typically 2–50 W.
- The schematic designator for a solenoid valve in ISA 5.1 P&IDs is SV (solenoid valve) or EV (electro-valve), tagged as XV-### in process diagrams where X denotes an on/off valve.
- Solenoid valves are classified as 2/2-way (two ports, two positions), 3/2-way (three ports, two positions), or 5/2-way (five ports, two positions) depending on the number of flow paths; the classification appears in the valve data tag adjacent to the symbol.
- Response time for a direct-acting solenoid valve is typically 10–100 ms, suitable for rapid PLC-controlled automation sequences.
- A pilot-operated solenoid valve uses a small pilot coil to shift a spool that routes main-line pressure to actuate a larger valve body, allowing a small low-power coil to control high-pressure, high-flow applications.
- The solenoid valve symbol has four pins: In (fluid inlet), Out (fluid outlet), Coil A (electrical coil terminal), and Coil B (electrical coil return).
Frequently asked questions
What does the solenoid valve symbol look like in a circuit diagram?
The Solenoid Valve symbol is a rectangle with a triangle inside pointing from left to right (indicating flow direction from In to Out). Two horizontal stubs on the left and right represent the fluid inlet (In) and outlet (Out) terminals. Two vertical stubs at the top and bottom represent the electrical coil connections (Coil A and Coil B) that energise the valve's electromagnet.
What does a solenoid valve do in an electrical control circuit?
A solenoid valve converts an electrical signal into a fluid flow switching action. When a PLC output, relay contact, or controller applies voltage to the coil terminals, the electromagnetic field pulls a plunger to open (or close) the fluid path between the In and Out ports. This allows electrical control logic to actuate pneumatic cylinders, water lines, gas supply, and other fluid systems.
What is the difference between a normally closed and normally open solenoid valve?
A normally closed (NC) solenoid valve blocks fluid flow when the coil is de-energised and opens when current is applied — the safe default is 'off'. A normally open (NO) solenoid valve passes fluid when de-energised and closes when energised — the safe default is 'on'. In schematics, NC or NO is annotated next to the solenoid valve symbol, and the same convention appears in the valve data tag.
What standard defines the solenoid valve symbol?
ISO 1219-1 and ISO 1219-2 define graphical symbols for fluid power systems, including solenoid-operated valve representations. ISA 5.1 (ANSI/ISA-5.1-2009) governs solenoid valve symbols in process and instrumentation diagrams (P&IDs). IEC 60617 covers electrical symbols but does not specifically define fluid valve symbols.
How many terminals does a solenoid valve symbol have?
The solenoid valve symbol in electrical schematics has four terminals: two fluid-path terminals (In and Out) and two electrical coil terminals (Coil A and Coil B). In P&ID conventions, the fluid path is shown separately from the instrument tag symbol, and only the electrical coil connections appear in the electrical schematic.
What voltage do solenoid valves operate at?
Solenoid valves are available in a wide range of operating voltages: 12 V DC and 24 V DC are most common in automation and control systems; 24 V AC, 110 V AC, and 230 V AC versions are used where AC power is directly available. The coil voltage must match the control circuit voltage; incorrect voltage will either fail to open the valve or burn the coil.
What is the designator for a solenoid valve in a schematic?
In ISA 5.1 process diagrams, solenoid valves are tagged as XV (on/off valve) followed by a loop number — for example, XV-101. In ladder logic and electrical schematics, the output coil is designated SV (solenoid valve) or EV (electro-valve) with a number. In pneumatic circuit diagrams per ISO 1219, the valve is assigned a number and the actuator type (solenoid) is shown graphically.
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