Coil and Accessories
More Than a "Black Box": An Engineer's Guide to AirTAC Solenoid Coils
In automation, the solenoid valve is the workhorse, but the real "brain" determining reliability is the often-overlooked "black box": the electromagnetic coil. Choosing the wrong coil leads to lost control signals, premature burnout, and catastrophic downtime. This guide analyzes the interconnected decisions an engineer must make—from AC/DC control philosophy to thermal insulation classes—to ensure system stability.
- AC vs. DC Control: Modern PLC standards (24VDC) offer silence and stability, while AC powerhouse options require careful sizing for inrush current.
- Connection Philosophy: Choose DIN (CDA) for 30-second maintenance swaps or Flying Leads (CLA) for high-vibration/washdown robustness.
- Thermal Endurance: Class B (130°C) is standard; Class H (180°C) is the mandatory armor for steam applications.
- Bore Differentiation: 116 Series (11.6mm) drives compact valves; 170 Series (17.0mm) shifts heavy 2-inch pistons.
1. The "Language" of Control: AC vs. DC
DC (The PLC Standard)
Measured in Watts (W). Steady power draw (6.5W for 116; 12.0W for 170). Ideal for solid-state transistor output cards, providing silent, spark-free operation.
AC (The Traditional Powerhouse)
Measured in Volt-Amps (VA). Inrush current can be 5-10x the holding VA. Fuses and power supplies must be sized for this surge, not just the steady-state load.
💡 THE "NO" POWER SURCHARGE:
Normally Open (NO) valves require ~40% more holding power (e.g., 35.0VA vs 25.0VA). This is because the coil must continuously fight a heavy-duty safety spring to maintain the closed state.
2. Connection Robustness: DIN vs. Flying Leads
CDA (DIN Connector): Modular Speed
The standard for modern automation. Allows for rapid coil swaps in under 30 seconds. Note: IP65 integrity is purely dependent on the terminal gasket seal. If missing or misaligned, moisture ingress will cause internal shorts.
CLA (Flying Leads): Hard-Wired Fortress
Sacrifices maintenance speed for vibration resistance. Used in mobile machinery or outdoor washdown zones. Leads can be run directly into IP68 waterproof junction boxes, eliminating the DIN connector weak point.
3. The Physics of Thermal Failure
A coil's total temperature is not just a factor of the weather. It is a cumulative thermal stack:
$$T_{Total} = T_{Ambient} + T_{Media} + T_{Self-Heating}$$
Class B (Standard): Limit is 130°C. Perfect for 40°C air or water. The 65°C self-heat rise keeps the total well below the threshold.
Class H (Steam-Ready): Limit is 180°C. Pair this exclusively with 2L series valve bodies handling 183°C steam. Class B coils will melt instantly in steam service due to media heat conduction.
4. Bore Selection: 116 vs. 170 Sizing
116 Series (11.6mm Bore)
The compact workhorse. Drives valves up to 1-inch (2S250). Draws 6.5W DC.
170 Series (17.0mm Bore)
The heavy lifter. Necessary for 2-inch pistons (2S500). Draws 12.0W DC to provide the magnetic force required to shift high-flow volumes.
Eliminating the "Coil-Killers"
Never treat solenoid coils as an afterthought. project success requires a thermal match (Class H for Steam), an electrical match (avoid DC/AC cross-wiring), and an environmental match (DIN for speed, Leads for vibration). By respecting the "black box" as a critical engineering decision, you secure the uptime of your automated facility.