Linear Solenoids Information

Last revised: November 19, 2024

Reviewed by: Scott Orlosky, consulting engineer

Linear solenoids convert electrical energy into mechanical power via a plunger with an axial stroke through either a pushing or pulling action. These transducers consist of a coil of wire, sometimes wrapped around an iron core, which generates a magnetic field when a voltage is applied. Because the magnetic field can be confined in a volume, its strength can be adjusted.

Linear solenoids can be either unidirectional (push or pull only) or bidirectional (push and pull). They are generally larger and significantly less expensive than rotary solenoids, but have fewer life cycles. When selecting products, buyers should consider maximum stroke, torque, and response time. Maximum stroke is the full linear travel of the solenoid’s plunger, from the fully-extended to the fully-seated position. The response time is the time needed to move the plunger full stroke under no load.

Types of Linear Solenoids

Linear solenoids are often classified as pull and/or push devices.

Pull solenoids bring the plunger into the solenoid’s body along the electromagnetic path. Applications include switchgear, valve actuation, brakes and clutches, and throttle control.
Push solenoids move the plunger out of the solenoid’s body. Often, they have a spring return to bring the plunger back to the home position when de-energized.

Bidirectional push/pull solenoids are also available. There are two subtypes: conical and flat. Conical devices are suitable for a medium-stroke or long stroke applications. Flat devices provide short strokes and strong force.

Solenoid Duty

In addition to push, pull and push/pull products, linear solenoids may be classified as continuous or intermittent.

Continuous duty solenoids are designed for operating conditions with continuous, heavy-duty use. They are more durable than intermittent solenoids and physically larger in size.
Intermittent duty solenoids are rated for on-off applications at less than 100% duty cycle. When used to control a valve, or gear engagement, they may be referred to as a Shift Solenoid

Solenoid Construction

The GlobalSpec SpecSearch database provides information about these linear solenoids, which are defined according to their construction.

Open-frame solenoids are box-like, C-frame, or D-frame devices with air gaps in their metal frames to provide heat dissipation. Small, open-frame devices are sometimes used in vending machines to dispense products.
Tubular solenoids are tube-shaped devices with a full metal case. They are designed to minimize flux leakage and operational noise.
Flapper solenoids feature a hinged design and are designed for low-force, long-life applications. They are sometimes called flappers. Applications include refrigerators ice chutes and the control of the airbox flap on motorcycles.
Laminated solenoids have a laminated frame and insulated laminations that allow the magnetic field to develop while minimizing eddy currents. Unlike other solenoids, which are designed for use with direct current (DC) power, laminated solenoids can use alternating current (AC) with a silicon bridge rectifier.

Linear Solenoid FAQs

How does the duty cycle of a solenoid affect its performance and lifespan in engineering applications?

The duty cycle is a measure of how often a solenoid is active compared to its total operational time. It is expressed as a percentage of the time the solenoid is energized versus the total cycle time, including both active and inactive periods.

Solenoids designed for continuous duty are built to handle continuous, heavy-duty use and are generally more durable than those designed for intermittent duty. Intermittent duty solenoids are rated for on-off applications at less than 100% duty cycle.

Operating a solenoid at a higher duty cycle than it is rated for can lead to overheating, since power is lost through heat. This can damage the solenoid's components, such as motors and circuits, and reduce its performance.

The lifespan of a solenoid is influenced by its duty cycle. A higher duty cycle can lead to increased wear and tear, reducing the solenoid's lifespan. This can also create excessive side loading, and particulate contamination. To ensure longevity, it is important to operate solenoids within their specified duty cycle limits.

When selecting a solenoid for a specific application, it is crucial to consider the duty cycle requirements to ensure that the solenoid can meet the application's demands without compromising performance or lifespan.

How can the duty cycle for a specific solenoid application be calculated?

The duty cycle is the ratio of the time a solenoid is active (energized) to the total cycle time, which includes both active and inactive periods. It is usually expressed as a percentage.

Identify the total time the solenoid is energized (active time) and the total time it is not energized (inactive time) within one complete cycle.

Use the formula, Duty Cycle = (On time)/(On time + Off Time)

For example, if a solenoid runs for 10 seconds and then rests for 40 seconds, the duty cycle would be: 10/(10 +40) = 10/50 = 20%.

Consider Application Requirements: Ensure that the calculated duty cycle aligns with the solenoid's specifications and the application's demands. Operating a solenoid beyond its rated duty cycle can lead to overheating and reduced lifespan.

What are the best practices for maintaining solenoid performance and durability?

Ensure that the solenoid operates within its specified duty cycle limits. Operating beyond these limits can lead to overheating and damage.

If the application requires a higher duty cycle, reduce the load or speed to prevent overheating.

Choose solenoids with appropriate construction for the application environment. For example, tubular solenoids minimize flux leakage and operational noise, which can enhance performance and durability.

Consider solenoids with robust construction and protective coatings if the application involves harsh environmental conditions. Particulates and corrosives are especially damaging.

Regularly inspect solenoids for signs of wear and tear, and ensure that they are operating within their specified parameters. This can help identify potential issues before they lead to failure.

Select solenoids that are specifically designed for the application's demands. For instance, continuous duty solenoids are more durable for heavy-duty use compared to intermittent duty solenoids.

How can environmental factors affect solenoid performance?

Particulate exposure and contamination can cause mechanical wear and interfere with the solenoid's operation by obstructing movement or causing abrasion on components.

Exposure to corrosive substances can degrade solenoid materials, leading to premature failure. Solenoids used in such environments may require protective coatings or resistant materials to maintain performance and durability.

Environmental conditions that result in excessive side loading can reduce the lifespan of a solenoid. This mechanical stress can cause misalignment or wear on the solenoid's components, affecting its ability to deliver the necessary force over the designed time.

Extreme high temperatures can lead to overheating, while low temperatures might cause materials to become brittle. Proper thermal management and material selection can mitigate these effects.

High humidity or moisture can lead to electrical issues such as short circuits or corrosion of electrical contacts. Solenoids in such environments may need sealing or encapsulation to protect against moisture ingress.