In-Depth Interpretation of Pneumatic Solenoid Valve Schematic Diagrams: Principle, Dissection, and Application Guide

In industrial automation pneumatic systems, the pneumatic solenoid valve is the core conversion element for "electrical signal to pneumatic action." Its operating principle is intuitively presented through standardized schematic diagrams. Understanding the component symbols, action logic, and path changes within the schematic is crucial for selection, commissioning, and maintenance. This article will start with the core components of a pneumatic solenoid valve schematic, dissect the working principle by type, explain how to interpret the diagrams, and match the principle to operating conditions using practical application scenarios, concluding with recommendations for high-quality, adaptable products.

I. Core Components of a Pneumatic Solenoid Valve Schematic: Symbol-to-Part Correspondence

Pneumatic solenoid valve schematics are drawn using internationally standardized pneumatic component symbols, primarily consisting of three major systems: "Electromagnetic Drive Module," "Spool Control Module," and "Fluid Port Module." The symbols for each module correspond directly to the physical parts, which is fundamental to understanding the principle:

Schematic Symbol Module	Corresponding Physical Part	Symbol Meaning and Function Description
Electromagnetic Drive Module	Solenoid Coil, Wiring Terminals	Symbol is a "box + lead wire" (e.g., $\square-\circ$), with voltage labeled (e.g., DC $24\text{V}$). Represents the electrical signal input unit, which generates electromagnetic force when energized to drive the spool.
Spool Control Module	Spool, Return Spring	Symbol is a "T-shaped / Rectangular Path + Spring Symbol." The T-shaped path represents the spool position, and the spring symbol ($\supset$) represents the return mechanism, indicating the spool's reset direction when de-energized.
Fluid Port Module	P/A/R (or T) Ports	Ports are labeled with letters: - P (Pressure): Air supply inlet, often marked with "$\rightarrow$" to indicate flow direction; - A (Actuator): Actuator outlet, connects to components like cylinders; - R (Release): Exhaust port, can be marked with "$\circ$" (Muffler).
State Indicator	Working Position / Initial Position	"Solid lines" represent the energized working position path; "dashed lines" represent the de-energized initial position path. Some symbols include "ON" (energized) and "OFF" (de-energized) labels.

Taking the schematic for the common "3/2-Way Pneumatic Solenoid Valve" as an example, the core logic is simplified: When de-energized (OFF), the spring pushes the spool to connect the A port to the R port (exhaust), and the P port is blocked. When energized (ON), the coil pulls the spool to connect the P port to the A port (supply), and the R port is blocked. The symbols of each module are connected via path lines, intuitively presenting the "electrical-to-pneumatic" conversion process.

 

II. Dissection of Main Pneumatic Solenoid Valve Types: Schematic and Working Principle

Based on the spool driving method, pneumatic solenoid valves are mainly divided into "Direct-Acting" and "Pilot-Operated" types. Their schematic structures and action logics differ significantly, matching different pressure and flow conditions, requiring targeted interpretation based on the schematic:

1. Direct-Acting Pneumatic Solenoid Valve: Schematic and "Direct Electromagnetic Drive" Principle

(1) Schematic Characteristics

The schematic for a direct-acting pneumatic solenoid valve lacks a "pilot path," containing only the core structure of "coil - spool - spring - three ports." The symbol feature is: the P port aligns directly with one end of the spool, with no branched paths. This type is suitable for scenarios with bore sizes $\le 10\text{ mm}$ and pressure $\le 0.8\text{ MPa}$ (e.g., vacuum suction cups, small cylinder control).

(2) Working Principle Dissection (Taking Normally Closed 3/2-Way as Example)

Step-by-step analysis of the action logic based on the schematic:

• De-energized Initial Position (OFF, Dashed Path on Schematic):

  The solenoid coil has no current (no "energized indicator" on the symbol). The return spring ($\supset$) is extended, pushing the spool to block the P port (air inlet). The A port (actuator outlet) and R port (exhaust port) are connected through the internal spool path. Residual compressed air in the downstream cylinder is exhausted through the R port, and the cylinder resets (e.g., retracts).

• Energized Working Position (ON, Solid Path on Schematic):

  The coil receives the rated voltage (e.g., DC $24\text{V}$, voltage value labeled on the symbol), generating electromagnetic force to pull the spool, overcoming the spring force and moving the spool toward the coil end. After the spool moves, the P port and A port are connected. Compressed air enters the cylinder via $\text{P} \to \text{A}$, pushing the cylinder to actuate (e.g., extend). The R port is blocked by the spool, stopping exhaust.

• De-energized Reset (Return to OFF State):

  The electrical signal is cut off, the coil's magnetic field disappears. The spring force pushes the spool to reset, re-blocking the P port and connecting the A-R ports. The system returns to the initial state, completing one "electrical-to-pneumatic" cycle.

(3) Key Schematic Interpretation Points

• No Pilot Hole Symbol: The direct-acting schematic lacks the "small-diameter pilot path" symbol (e.g., fine lines of $\phi 1\text{-}2\text{ mm}$), allowing for quick distinction from pilot-operated types.

• Vacuum Adaptability: If the schematic is marked with "$-0.09\text{ MPa}$" (vacuum range), it indicates the spool uses a design without a sealing blind area, allowing stable operation in a vacuum environment.

2. Pilot-Operated Pneumatic Solenoid Valve: Schematic and "Pressure Differential Assisted Drive" Principle

(1) Schematic Characteristics

The schematic for a pilot-operated pneumatic solenoid valve includes a two-stage structure: "Pilot Valve + Main Valve." The symbol feature is: the P port splits into two paths—one connects to the pilot valve via a "pilot hole" (fine line), and the other connects to the main valve's lower chamber. The coil symbol is next to the pilot valve, and the main valve has large-diameter paths (corresponding to bore size $\ge 15\text{ mm}$). This type is suitable for pressure $0.15\text{-}1.0\text{ MPa}$ and high-flow scenarios (e.g., heavy-duty cylinders, main production line air supply).

(2) Working Principle Dissection (Taking 5/2-Way Pilot-Operated as Example)

Analysis of the dual-stage drive logic based on the schematic (5/2-Way includes $\text{A}/\text{B}$ dual actuator ports and $\text{R}1/\text{R}2$ dual exhaust ports, better suited for double-acting cylinder motion):

• De-energized Initial Position (OFF):

  The pilot valve coil is de-energized. The pilot spool, driven by the spring, blocks the "P $\to$ Pilot Upper Chamber" path and connects the "Pilot Upper Chamber $\to$ R1" exhaust. The main valve's upper chamber connects to R1 via the pilot path, dropping the pressure to atmospheric. The main valve's lower chamber is directly connected to the P port (high pressure). Under the pressure differential of "lower chamber high pressure - upper chamber low pressure," the main spool moves upward, connecting the "P $\to$ B" and "A $\to$ R2" paths. Compressed air enters the cylinder rod-end via $\text{P} \to \text{B}$, pushing the cylinder to retract. Air from the head-end exhausts via $\text{A} \to \text{R2}$.

• Energized Working Position (ON):

  The pilot valve coil is energized, pulling the pilot spool to move, blocking the "Pilot Upper Chamber $\to$ R1" path and connecting the "P $\to$ Pilot Upper Chamber." High-pressure air enters the main valve's upper chamber via the pilot hole, increasing the pressure there. At this point, the main valve has "upper chamber high pressure - lower chamber high pressure" (pressure balance). The force from the pilot spool pushes the main spool downward, connecting the "P $\to$ A" and "B $\to$ R1" paths. Compressed air enters the cylinder head-end via $\text{P} \to \text{A}$, pushing the cylinder to extend. Air from the rod-end exhausts via $\text{B} \to \text{R1}$.

• De-energized Reset (OFF):

  The pilot valve coil is de-energized, the pilot path returns to its initial state, and the main valve's upper chamber exhausts and depressurizes. The pressure differential pushes the main spool to reset, switching the path back to "P $\to$ B" and "A $\to$ R2," completing the cycle.

(3) Key Schematic Interpretation Points

• Pilot Hole Symbol: Fine lines (usually $1/3$ thinner than the main path) represent the pilot path, which is the key identifier distinguishing pilot-operated from direct-acting types.

• Pressure Differential Indicator: If the schematic is marked with "$\Delta\text{P} \ge 0.1\text{ MPa}$," it means the main valve requires a minimum pressure differential to operate and is unsuitable for low-pressure ($\le 0.1\text{ MPa}$) scenarios.

 

III. Key Interpretation Points for Pneumatic Solenoid Valve Schematics: Master Core Logic in 3 Steps

For actual selection or maintenance, quickly interpreting a pneumatic solenoid valve schematic should follow the three-step method: "Identify Symbols $\to$ Determine Type $\to$ Analyze Path," to avoid selection errors caused by misreading:

1. Step 1: Identify Core Symbols and Clarify Component Function

• Port Labels: Confirm the positions of P/A/R (or T) ports to avoid reversing the air source and actuator (e.g., reversing the P port may cause spool jamming).
• Coil Symbol: Check the voltage label (e.g., AC $220\text{V}$, DC $24\text{V}$) to ensure it matches the control system's power supply.
• Spring Symbol: Determine the reset direction (the end where the spring is located is the initial position where the spool rests) to clarify the path state when de-energized.

1. Step 2: Determine Solenoid Valve Type Based on Path Structure

• No Pilot Hole $\to$ Direct-Acting: Suitable for low-pressure, vacuum, and small-flow scenarios. When selecting, confirm the "minimum operating pressure" (direct-acting can start at $0\text{ MPa}$).
• Has Pilot Hole $\to$ Pilot-Operated: Suitable for high-pressure, high-flow scenarios. When selecting, confirm the "minimum pressure differential" (usually $\ge 0.1\text{ MPa}$), to prevent failure to drive under low pressure.

1. Step 3: Analyze On/Off Logic to Match Operating Conditions

• Energized/De-energized Path: Based on the "solid/dashed" path on the schematic, confirm whether the actuator's action direction (e.g., cylinder extension/retraction) matches the process requirements.
• Exhaust Port Design: If the schematic's R port is marked with a "muffler symbol ($\circ$)," it indicates a need for a muffler to reduce noise, suitable for noise-sensitive environments like workshops. If marked with a "check valve," it is suitable for dusty environments that require preventing external contaminants from entering.

 

IV. Matching Principle with Operating Conditions: From Schematic to Practical Application

 

The pneumatic solenoid valve's principle design directly determines its applicable scenarios. The core parameters reflected in the schematic (type, pressure, flow) must be matched to the actual operating conditions. The specific correspondences are as follows:

Solenoid Valve Type	Core Schematic Feature	Applicable Operating Conditions	Typical Application Scenarios
Direct-Acting	No pilot hole, P port directly connected to spool	Pressure $0\text{-}0.8\text{ MPa}$, bore $\le 10\text{ mm}$, vacuum environment	Vacuum cup holding, small pneumatic gripper control
Pilot-Operated	Has pilot hole, main/pilot dual path	Pressure $0.15\text{-}1.0\text{ MPa}$, bore $\ge 15\text{ mm}$, high flow	Heavy-duty cylinder drive, main production line air control
3/2-Way	Single actuator port (A)	Actuator single-direction motion (e.g., single-acting cylinder)	Silo gate opening/closing, suction cup lifting control
5/2-Way	Dual actuator ports (A/B)	Actuator bidirectional motion (e.g., double-acting cylinder)	Robotic arm extension/retraction, conveyor belt start/stop control

 

V. Preferred Recommendation: Airtac Pneumatic Solenoid Valve Principle Optimization and Performance Advantages

 

Based on the above working principle and scenario matching logic, Airtac (Yadeke) pneumatic solenoid valves have become a preferred choice for industrial pneumatic systems through targeted optimization of principle-related components, achieving "full-scenario adaptability, high reliability, and easy maintenance":

1. Principle Design Adapts to Diverse Conditions, Covering All Type Requirements

   Airtac offers two major series of pneumatic solenoid valves, Direct-Acting and Pilot-Operated, precisely matching different principle needs:

• Direct-Acting Series (e.g., 2V Series): Schematic shows no pilot hole. The spool uses precision grinding ($\text{Ra} \le 0.8\text{ μm}$ roughness) for stable starting in the $0\text{-}0.8\text{ MPa}$ range, suitable for vacuum ($\le -0.09\text{ MPa}$) scenarios. For example, the 2V025-06 model is suitable for small pneumatic systems with $\phi 4$ tubing.
• Pilot-Operated Series (e.g., 4V Series): Schematic's main/pilot dual path is optimized. The pilot hole diameter is precisely controlled ($\phi 1.2\text{ mm}$), ensuring stable driving with a minimum pressure differential of just $0.15\text{ MPa}$. The 4V210-08 model has a G1/4 bore, suitable for medium-sized cylinder control with $\phi 6/8$ tubing.
• Special Types (e.g., 5/2-Way with Feedback): Schematic includes a "position sensor symbol" for real-time spool position feedback, suitable for automated production lines requiring precise monitoring (e.g., automotive part assembly lines).

1. Core Component Optimization, Enhancing Principle Reliability

   Airtac has upgraded the critical components (coil, spool, seals) relevant to the pneumatic solenoid valve's principle to prevent principle-based failures:

• Coil: Uses $155^\circ\text{C}$ temperature-resistant enameled wire with a flame-retardant skeleton, preventing overheating even during high-frequency operation (e.g., 30 switches per minute), extending the electromagnetic drive module's lifespan.
• Spool: Direct-acting types use stainless steel; pilot-operated types use hard anodized aluminum alloy, increasing wear resistance by $50\%$, preventing poor path sealing from long-term operation.
• Seals: Uses NBR (Nitrile Rubber) or FKM (Fluoro-Rubber), compatible with air, inert gases, etc. Leakage is $\le 0.1\text{ mL/min}$, far exceeding industry standards, ensuring the on/off logic in the schematic is precisely achieved.

1. High Consistency Between Schematic and Physical Product, Reducing Commissioning Difficulty

   Airtac's product manuals provide "1:1 standardized schematics" with detailed parameters (voltage, pressure, bore), and the physical ports and coil position exactly match the schematic:

• Port Labeling: Physical P/A/R ports are laser-engraved, consistent with the schematic, preventing reversed connections.
• Commissioning Aid: Some models (e.g., 4V310 series) feature a "manual override button" on the valve body, allowing simulation of the energized action to directly verify the path logic in the schematic without extra wiring tests, improving commissioning efficiency.

Conclusion

The pneumatic solenoid valve schematic is the "visual language" of its operational logic. Understanding the meaning of the symbols, the type differences, and the path changes is the foundation for achieving "accurate selection and efficient commissioning." Airtac pneumatic solenoid valves translate the ideal logic from the schematic into stable, real-world performance by optimizing the principle design and core components, adapting to diverse conditions from low-pressure vacuum to high-pressure, high-flow. Whether for fine control in small equipment or high-efficiency driving in large production lines, Airtac provides principle-matched, reliably performing pneumatic solenoid valve solutions, making it a trustworthy choice for industrial automation pneumatic systems.