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A solenoid valve operates on the electromagnetic force generated by its coil, controlling mechanical motion by switching the coil current on and off. Inside the valve is a sealed cavity with several through-ports, each connected to a different hydraulic line. A piston sits in the cavity, flanked by electromagnets on both sides. When one electromagnet is energized, the piston is pulled toward it, opening or closing the corresponding drain ports. The inlet port stays open at all times, allowing hydraulic oil to flow into the selected drain line, which then pushes the cylinder piston and rod to drive the mechanical load. In short, you control the machine's movement simply by cycling the electromagnet's current.
Solenoid Valve Types and Key Characteristics
1. Direct-acting solenoid valve: With power off, the valve stays closed; when energized, the coil's electromagnetic force lifts the valve open. This type handles vacuum, negative pressure, and zero-pressure conditions, though the orifice size is typically limited.
2. Step-by-step direct-acting solenoid valve: This combines direct-acting and pilot-operated principles. It opens directly when powered if there's no pressure differential; when a differential exists, it uses both electromagnetic force and line pressure to open. It closes on power-off. It suits zero-differential, vacuum, and high-pressure systems, but draws more power and must be mounted horizontally.
3. Pilot-operated solenoid valve: When energized, the pilot port opens, using the pressure differential to shift the main valve open. De-energized, the pilot closes and the valve shuts. This design is compact, low-power, and handles higher fluid pressures. It can be mounted in any orientation, but the system must maintain the required pressure differential.
When selecting a solenoid valve, you also need to factor in fluid properties (media type, temperature range, state, and viscosity), pressure ratings (nominal and working), electrical specs (voltage), duty cycle, and environmental requirements (explosion-proof, check function, manual override, waterproof/fog-proof, spray resistance, or submersible). All these variables directly affect valve performance and service life.