Motor Controls

Solenoids 331

Solenoids introduces different types of solenoids and their uses. Solenoids use magnetic induction to produce linear motion. Common solenoid types are direct action, plunger, bell-crank, and clapper. Solenoids are rated by their voltage and current characteristics, which helps determine the appropriate solenoid for a given application. Solenoid failure may be caused by selecting the wrong solenoid, or other common causes such as incorrect voltage or frequency.

Understanding how solenoids work is necessary for working with the many applications that utilize them, including combustion engines and industrial fluid control systems. After taking this class, users will have an understanding of solenoids and should be able to identify important factors in solenoid selection and common causes of solenoid failure. Knowing how to choose the correct solenoid and avoid solenoid failure decreases the chances of solenoids burning out or needing to be replaced for other reasons.

  • Difficulty Advanced

  • Format Online

  • Number of Lessons 18

  • Language English


Or fill out this form and a specialist will contact you shortly

Course Outline
  • Solenoids
  • Solenoid Function
  • Solenoid Cycling
  • Solenoid Selection
  • Coil Characteristics
  • Solenoid Basics Review
  • Direct Action Solenoids
  • Plunger Solenoids
  • Plunger Solenoid Operation
  • Bell-Crank Solenoids
  • Clapper Solenoids
  • Indirect Action Solenoid Operation
  • Solenoid Configurations Review
  • Solenoid Laminations
  • Solenoid Air Gaps
  • Common Solenoid Failures
  • Voltage Failures
  • Final Review
  • Describe solenoids.
  • Describe how a solenoid works.
  • Describe how a solenoid works.
  • Describe factors involved in solenoid selection.
  • Describe solenoid coil characteristics.
  • Describe direct action solenoids.
  • Describe a plunger solenoid.
  • Describe a plunger solenoid.
  • Describe a bell-crank solenoid.
  • Describe a clapper solenoid.
  • Describe a bell-crank solenoid. Describe a clapper solenoid.
  • Describe the purpose of laminations.
  • Describe the purpose of an air gap.
  • Describe common causes of solenoid failure.
  • Describe voltage failures in solenoids.
Vocabulary Term


Alternating current. Electricity that reverses direction at regularly recurring intervals of time. AC switches direction 60 times per second, or 60 hertz (Hz), in the US.

air gap

A small space left between the solenoid core and the armature to interrupt the magnetic field. The air gap prevents the armature from getting stuck in the closed position even when the solenoid is de-energized.

alternating current

AC. Electricity that reverses direction at regularly recurring intervals of time. Alternating current switches direction 60 times per second, or 60 hertz (Hz), in the US.


The movable part of a solenoid. The armature performs the solenoid's work.

bell-crank solenoid

A solenoid that uses a lever attached to the armature to soften the impact of the linear force. Bell-crank solenoids are used to latch machine guards.


A solenoid failure caused by overheating of the coil. Burnout may be caused by several factors, including incorrect current and voltage levels.


The occasional unwanted vibration between components. Chatter in solenoids can be prevented by including an air gap.


A controlled path for electricity. A circuit is energized when it is closed and de-energized when it is open.

clapper solenoid

A solenoid with an armature that hinges on a pivot point to produce a gradual force. Clapper solenoids are used in motor starters.


Multiple loops of conducting wire used to create a magnetic field when current passes through it. Coils are often wrapped continuously around magnetic cores made of iron or steel.


A material that allows electricity to flow easily. Conductors are typically metals.


Connecting points between two conductors that allow electricity to flow when they are closed. Contacts prevent the flow of electricity when open.


The flow of electricity. Current strength is called amperage and is measured in amperes (A).


One complete motion of a solenoid from its resting position to full extension and back. The cycle begins when the solenoid starts to shut and ends after it has opened again after sealing.


Direct current. Electricity that flows in one direction. DC does not reverse the direction of flow.

digital multimeter

DMM. A device that can measure voltage, current, or resistance. A digital multimeter is the most versatile and common meter used today for electrical maintenance.

direct action solenoids

Solenoids that use the armature to output liner motion. Direct action solenoids include horizontal, vertical, and plunger solenoids.

direct current

DC. Electricity that flows in one direction. Direct current does not reverse the direction of flow.

duty cycle

A rating of solenoid life expectancy based on the number of operations per minute. Duty cycle is given as a percentage.

eddy current loss

An efficiency loss caused by heat generated by circulating currents. Eddy current loss can be prevented in solenoids by using laminations instead of solid cores.

efficiency loss

The reduction of energy due to natural effects, which cause the energy output to be less than energy input. Efficiency losses can be minimized with good design, but no system is 100% efficient.

fluid systems

A power transmission system that uses the force of flowing liquids or gases to transmit power. Fluid systems include hydraulic systems and pneumatic systems.


The number of complete AC cycles that occur in one second. Frequency is measured in hertz (Hz).


Hz. A unit of measurement indicating the frequency of alternating current. One hertz is equal to one cycle per second.

horizontal action solenoid

A simple solenoid in which the armature makes a direct side-to-side movement. Horizontal action solenoids are used on conveyor belts.

hydraulic systems

A power transmission system that uses the force of flowing liquids to transmit power. Hydraulic systems often use solenoids to control valves.

indirect action solenoids

Solenoids that use additional or specially designed components to absorb and/or redirect the armature's force. Indirect action solenoids include bell-crank and clapper solenoids.

induction motors

An AC motor that uses magnetic induction to produce rotation. Induction motors often can create transient voltages as they turn on and off.

inrush current

The initial surge of electrical current into a device. Inrush current can be up to 10 times higher than the device’s normal operating current because there is low initial resistance.


Thin sheets of metal sealed together to form the core of a solenoid. Laminations help prevent eddy current loss.

linear motion

Motion that takes place in a straight line. Solenoids generate linear motion.

machine guards

A rigid shield or cover that encloses hazardous areas on a machine. Machine guards prevent accidental machine contact with body parts and prevent debris, such as chips, from exiting the machine.

magnetic field

The area in and around a magnet in which a magnetic force exists. Magnetic fields exhibit the powers of attraction and repulsion.

magnetic flux

The force that surrounds a magnet and exhibits the powers of attraction and repulsion. Magnetic flux is described as imaginary lines of force that exit one pole of a magnet and return to the other.

magnetic induction

The use of current in a conductor to create a magnetic field. Magnetic induction occurs when current flows through a wire, creating magnetic lines of flux around the wire.

motor starters

An electrically operated device that starts a motor when triggered. Motor starters use magnetic induction to provide the startup current for a motor.

operating current

The electrical current level needed to keep a device energized. Operating current is lower than inrush current.

plunger solenoid

A solenoid that uses a spring-loaded iron rod. The plunger solenoid's rod aligns with the magnetized coil when energized, creating linear motion.

pneumatic systems

A power transmission system that uses the force of flowing gases to transmit power. Pneumatic systems often use solenoids to control valves.


Having two oppositely charged poles, one positive and one negative. Polarity determines the direction in which current flows.


A physical setting on a directional control valve. The position of a valve determines how it directs fluid flow.


The resistance to the flow of alternating current due to inductance. Reactance decreases current flow in AC solenoids.

residual magnetism

The attractive force that exists in an electromagnetic object after it has been de-energized. Residual magnetism can cause a solenoid's armature to get stuck in the sealed position.


The opposition to current flow. Resistance is measured in ohms (Ω).


An output device that uses a conductive coil to convert electrical energy into linear mechanical motion. Solenoids are often used to control valves in fluid power systems.


A description of the essential physical and technical properties of a circuit or a device. Specifications are sometimes called specs.


The distance a solenoid armature travels to close completely. The stroke length affects solenoid operation and wear.


The acceptable deviation from a specified dimension. Tolerances indicate the allowable difference between a physical feature and its intended design.

transient voltage

A short surge of voltage, often occurring before steady-state conditions have become established. Transient voltages can damage electrical devices such as solenoids.


A loop or wrap of conducting wire in a coil. The number of turns in a coil affects the strength of the magnetic field.


A mechanical device used to regulate the flow of liquid, gas, or other objects. Valves have movable parts that open, close, or obstruct one or more openings or passageways.

vertical action solenoid

A simple solenoid in which the armature makes a direct up-and-down movement. Vertical action solenoids are used with engine valves.


The electrical pressure or potential that pushes electrons through a conductor. Voltage is measured in volts (V) and is also called electromotive force.