A coil, magnetic path and moving part.
A solenoid actuator uses a coil to create a magnetic field and move a plunger or armature. A spring or other force may return the mechanism when the coil is de-energised.
The word solenoid can mean the coil itself or the complete actuator. A solenoid valve combines electromagnetic actuation with a valve mechanism.
Follow a simple spring-return actuator.
- Coil energisedCurrent produces a magnetic field.
- Plunger movesMagnetic force overcomes the opposing forces.
- Coil de-energisedA return spring restores the starting position.
Movement changes the valve’s condition.
In one direct-acting, normally closed valve, a plunger lifts a seal from a seat when energised. A normally open design can instead close when energised.
Other designs use a small pilot stage to control a larger flow path. “Coil on” does not universally mean “valve open”, and valve movement does not itself create hydraulic pressure.
The electrical command is one part of the result.
The controller energises a coil; the actuator influences a valve; the valve changes a fluid path. The actual movement also depends on the hydraulic circuit and mechanical condition.
This is why a working electrical signal alone does not prove the valve or lift has responded correctly. Later hydraulic lessons will connect valves to pumps, pressure and flow.
Coils are designed for particular conditions.
Rated voltage, AC or DC operation, temperature and duty all matter. Some actuators are designed for continuous energisation and others for intermittent use.
Proportional solenoids allow controlled movement or force over a range. They require the intended control electronics and are not just ordinary on/off coils with an arbitrary voltage applied.
A closer look
Actuator force changes with the magnetic circuit, current and air gap. Heating and spring or fluid forces also affect operation. An audible click is evidence of some movement, not proof of full travel or the intended flow.
Check your understanding
Does energising every solenoid valve open its flow path?
Reveal the explanation
No. A normally open valve can close when energised, and pilot-operated arrangements can be more complex. The valve’s function determines the result.