Solenoid Valves: How They Work, Types, and Industrial Applications

Solenoid valves are electromechanically operated valves that use the magnetic force generated by an electric coil (solenoid) to open or close the valve. They are among the most widely used valve types in automated systems because of their fast response, compact size, and easy integration with electrical control systems. From simple on-off water supply control to complex pneumatic and hydraulic automation circuits, solenoid valves provide reliable, repeatable, and cost-effective flow control across dozens of industries.

How a Solenoid Valve Works

When an electric current passes through the coil wound around the valve body, it generates a magnetic field that pulls a ferromagnetic plunger (core) upward against a spring. The plunger movement either directly opens or closes the valve orifice, or in pilot-operated designs, shifts a pilot port that uses process pressure to move the main disc. When the current is switched off, the spring returns the plunger to its original position. Direct-acting solenoid valves can operate at zero differential pressure, while pilot-operated designs require a minimum pressure differential to function but can control much larger flows with a small coil.

• Direct-acting: coil directly moves the valve element, works at zero differential pressure

• Pilot-operated (indirect): coil opens a pilot port, process pressure moves the main disc

• Semi-direct (servo-assisted): combines direct and pilot operation for intermediate flow ranges

• Normally closed (NC): valve closed when de-energized, opens when coil is energized

• Normally open (NO): valve open when de-energized, closes when coil is energized

Coil and Electrical Specifications

Solenoid coils are available for AC and DC power supplies. AC coils (typically 24V, 110V, or 230V) are simpler and less expensive but generate more heat and audible hum at steady state. DC coils (typically 12V or 24V) operate more quietly and generate less heat, making them preferred for continuous duty applications and environments sensitive to electrical noise. Enclosure ratings (IP65, IP67, ATEX/IECEx for hazardous areas) must be appropriate for the installation environment. Coil power consumption ranges from a few watts for small valves to over 100 watts for large industrial solenoids.

• IP65/IP67: protection against dust and water jets or temporary immersion

• ATEX/IECEx Ex d or Ex m: certified for use in explosive atmospheres

• Class F or H insulation for high-ambient-temperature installations

• Manual override feature allows valve operation during power failure or commissioning

• LED status indicator on coil provides visual confirmation of energized state

Common Industrial Applications

Solenoid valves are indispensable in pneumatic systems, where they control air flow to cylinders, actuators, and air tools. In water and irrigation systems, solenoid valves automate the opening and closing of water supply to zones. Chemical dosing systems use small solenoid valves for precise metering. Hydraulic power units use high-pressure solenoid valves to direct oil flow to cylinders and motors. HVAC systems rely on solenoid valves for refrigerant circuit control in chillers and heat pumps. Medical equipment uses miniature solenoid valves for gas and liquid routing in analyzers and ventilators.