Solenoid Valve Basics
A solenoid valve is a simple yet elegant electromechanical device that controls the flow of liquid or gas. When power to its metallic coil (solenoid) is switched on, the resulting magnetic field causes a plunger (or other actuator) inside the coil to move, opening the valve and allowing fluid flow. When the current is turned off, the plunger and valve return to their original positions, ending fluid flow.
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Design
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Solenoid valves can have from two to five ports. In the case of a two-port valve, the actuator opens or closes the valve, allowing or blocking the flow of liquid or gas. In the case of a three-port valve, the flow is switched between two outlet ports. Multiple solenoid valves are sometimes positioned together on a manifold. The type of actuator most frequently used is a plunger. Other types are piloted armature and rocker. Because there is no mechanical device forcing fluids through the valve, there must be a pressure differential between the inlet and outlet pipes, with the inlet pressure higher. The most common voltages range from 6-volt DC to 220/240-volt AC. Seal (diaphragm) materials include metal, rubber, fluoroelastomer and polytetrafluoroethylene. Solenoid valves are made from stainless steel, brass and plastic.
Types
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Solenoid valve types include normally open and normally closed, direct acting, semidirect acting, pilot operated, pinching and latching. The plunger directly opens and closes a hole inside the valve in direct-acting solenoid valves. In pilot-operated valves, also known as "servo" valves, the plunger opens and closes an opening in a pilot valve. Pilot valves are controlled with much less power, but they are slower. Pilot solenoid valves usually required full power to open and remain open. Direct-acting solenoid valves may only require full power for a brief period to open, and then lower power to hold that position. Latching valves do not require power to remain in the energized position. The inlet pressure through the pilot orifice opens and closes the solenoid valve seal.
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Uses
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Solenoid valves are essential components in a wide variety of machinery, devices and equipment including street sweepers, refrigerators, automatic faucets and industrial processing equipment. Used in fluid power pneumatic and hydraulic systems, solenoid valves control cylinders, fluid power motors and larger industrial valves. They control water flow into washing machines and dishwashers. In paintball equipment, solenoid valves usually control a larger valve controlling the propellant. Solenoid valves are also found in automatic irrigation sprinkler systems and in pharmacological experiment equipment. When a solenoid valve in a motor vehicle wears out, the vehicle won't start. It is important in the automobile parts industry.
Significance
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The most frequently used controls in fluidics are solenoid valves. They release, distribute, mix and shut off fluids. They provide fast and safe switching, compact design, high reliability and long service life.
Warning
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When performing maintenance on solenoid valves, turn off the power and wait 30 minutes before opening. Otherwise, the coil could burn out.
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