Choosing the Right Solenoid: A Comprehensive Guide for Latching and Push-Pull Options

How to select the latching solenoid or the push-pull solenoid, we would like to give your A Comprehensive Guide as a professional solenoid manufacturers to clearly working principles, function and application of the two kinds of the solenoid, and analyze it features as below:

Part one :  latching solenoid or push-pull solenoid Classification:

1.1. latching solenoid is divided into single latching solenoid and bistable latching solenoid.

1.2. Push-pull solelnoid is divided into push solenoid and pull solenoid

1.3 bistable latching solenoid.

Description of working state of bistable latching solenoid.(reference the above structure ): When the bistable latching solenoid is energized in the forward direction, the solenoid coil generates magnetic force to magnetize on the fixed iron core, and the fixed iron core will attract the iron core to move to the left. The attraction force is greater than the attraction force of the permanent magnet, and the object on the right iron core mechanism needs to be driven to move. When the coil is energized in the reverse direction, it generates magnetic force to magnetize on the fixed iron core  and the iron core moves to the right. The magnetic attraction force is greater than the holding force of the permanent magnet , and the pulling force applied is greater than the weight movement of the mechanism on the iron core.

After the power is off, the iron core is fixed by the permanent magnet, and the holding force is a fixed value. When the pulling force applied on the left and right sides is greater than the holding force of the permanent magnet, the iron core can be pulled to move.

1.4 Single latching solelnoid

The permanent magnet is installed at one end close to the object. When the power is on, the solenoid coil generates an attraction force, which is greater than the holding force of the permanent magnet and greater than the pulling force of the mechanism. After the power is off, the iron core is kept stationary, and the mechanism is kept unchanged by continuous pulling. The reverse energized coil conducts magnetism on the permanent magnet, releasing the same magnetic pole as the contact surface of the permanent magnet, thereby weakening the holding force of the permanent magnet, and the iron core can be ejected with the help of the spring to drive the mechanism to move. After the power is off, the permanent magnet resumes normal attraction, keeps the iron core out of the mechanism, and waits for the iron core to retract again when the power is on again.

1.5 Push-pull solenoid

It is the most common design among electromagnet types. The energized iron core retracts, and the de-energized iron core is ejected by a spring or mechanism, and the re-energized element forms a reciprocating motion.

Part Two:  latch solenoid VS Push-pull solenoid

2.1 Parts: The latching solenoid has one more set of permanent magnets than the push-pull solenoid.

2.2 DC Power source : The power-on of permanent magnets is divided into forward power-on and reverse power-on, while the power-on sequence of push-pull electromagnets is not divided.

2.3 working Stroke: The stroke of the latching solenoid is shorter than that of the push-pull solenoid, because the latching solenoid needs to overcome the holding force of the permanent magnet when it is powered on.

2.4 Strength: The latching solenoid generates a pulling force (such as the holding force of the permanent magnet is 2kg) when it is powered on. The mechanism requires a pulling force of more than 50g to pull. Then the current pulling force of the permanent magnet is only 50g, and after the power is off, a holding force of 2kg can be applied to keep the iron core. If the push-pull electromagnet needs to keep the iron core applying force for a short or long time, it is necessary to set the power-on time to meet the requirements.

2.5 On-off frequency: Most of the on-off time of the latching solenoid is designed to be instantaneous power-on and instantaneous power-off. (Power off) The permanent magnet attracts and holds the iron core to achieve continuous work. The push-pull electromagnet will set the power-on time according to the current needs of the equipment, and the continuous power supply meets the requirements.

2.6 Energy consumption: The latching solenoid works instantly and is kept working by the permanent magnet after power failure. The push-pull electromagnet has no power guarantee after power failure, and may move due to inertia or gravity pulling the iron core. Basically, the mechanism has been limited, and it will be powered on and run normally every time it works, which consumes more energy.

2.7 Price: The latching solenoid has permanent magnet blocks and a large number of solenoid coils. The overall cost is 1~2 times more expensive than the push-pull solenoid .

2.8 Lifespan: The lifespan of the solenoid is determined by the material and material processing. For conventional types, the latching solenoid has a shorter life, and the permanent magnet will slowly weaken its magnetism over time.

2.9 Function: The functions that the latching solenoid can do can be done by the push-pull solenoid. The characteristic of choosing the holding type is that a large force is required to keep working after power failure. The long-stroke push-pull electromagnet is powered on for a long time and works at high power to meet the holding force, so a permanent magnet is used to keep working continuously.

Part Three ： The principle, function and application of latching solenoid and push-pull solenoid are compared as follows:

3.1 Both working Principle  

latching solenoid: Permanent magnets are used inside. When the coil is energized, the slide moves toward the iron core and eventually stops at the end position. After the power is cut off, the slide remains in its original position due to the magnetic field generated by the permanent magnet. To return the slide, a reverse voltage or current must be applied. It is divided into unidirectional self-holding and bidirectional self-holding. The unidirectional self-holding only holds the iron core at one position at the end of the stroke. The bidirectional self-holding electromagnet adopts a double coil structure, which can hold the iron core at two different positions at the beginning and end of the stroke, and the two positions have the same output torque.

Push-pull Solenoid : A conductive winding matching its power is wound around the outside of the iron core. When powered on, according to the Ampere loop theorem, a magnetic field will be generated around the iron core, magnetizing the movable iron core in the middle, generating a forward or backward movement, pushing or pulling the load. After power failure, the moving iron core is reset by a spring.

3.2 Functional comparison

latching solenoid

Self-locking function: It has good self-locking performance and can maintain the position of the slide bar after power failure. It does not need to continuously consume electricity to maintain the state, which can save energy and avoid position changes caused by accidental power failures.

Precise positioning: Especially the bidirectional holding electromagnet can accurately hold the iron core in two different positions, with high positioning accuracy, and can be used in occasions requiring precise position control.

Push-pull Solenoid

Fast action: It can quickly realize the push or pull action, with fast response speed, can complete the action cycle in a short time, and has a high operating frequency7.

Strong dynamic load capacity: It can generate a large thrust or pull force when powered on, and can effectively push or pull the load. It is suitable for loads that require frequent push and pull operations.

3.3 Application  

latching solenoid

Power system: It is used for the opening and closing control of high-voltage switches. It can keep the switch in the open or closed state when the power is off to ensure the stable operation of the power system.

Aerospace: For example, the locking of the position of the flaps and landing gear of the aircraft can ensure that these components remain in the correct position even if there is an electrical failure during the flight.

Smart door lock: It can be used in some high-end smart door locks. When the door is closed, the electromagnet remains locked and will only be released when the correct unlocking signal is received.

Push-pull Solenoid

Automated production line: It is often used in the pushing and sorting of materials, such as pushing products from one station to another, or pushing products into different channels in the sorting system.

Automotive field: In the car door locks, seat adjustments, wipers and other parts, fast push-pull actions can be achieved to meet the various functional requirements of the car.

Medical equipment: In some medical equipment, such as the push rod control of the syringe, the lifting and lowering adjustment of the medical bed, its fast and stable push-pull function is used to achieve the corresponding operation.

3.4 Features:

Action requirements: If you need to push and pull quickly and frequently, such as pushing and sorting materials on the automated production line, push-pull solenoid are more suitable, with fast response speed and high operating frequency.  If frequent movements are not required, but the position is maintained for a long time in a specific position, such as component locking in aerospace, smart door locks, etc., then the latching solenoid is better choice

 Positioning accuracy: Holding electromagnets, especially bidirectional holding types, can accurately hold the iron core in two different positions with high positioning accuracy. If the application scenario requires high position accuracy, such as some precision instruments, specific station positioning in automatic control equipment, etc., holding electromagnets can be selected. For occasions where only simple push and pull actions are required and positioning accuracy is not high, push-pull electromagnets can meet the requirements.

3.5 Loading capacity

Static load: Holding electromagnets can provide stable holding force in the holding state, and can be used in situations where static loads need to be withstood for a long time, such as the opening and closing holding of high-voltage switches in power systems. Push-pull electromagnets mainly generate thrust or pulling force to overcome the load when energized, and generally have no holding force when static.

Dynamic load: Push-pull electromagnets can generate large thrust or pull when energized, and can effectively push or pull loads. They are suitable for occasions where frequent push-pull operations are required to overcome dynamic loads, such as car seat adjustment, wipers, etc. Although holding electromagnets can also provide a certain dynamic load capacity, their main advantage is usually the holding function.

3.6 Energy consumption

Long-term power-on situation: Holding electromagnets do not need to consume electricity continuously in the holding state, and only need to be energized when changing the state, which can save energy and is suitable for scenes that need to maintain a certain state for a long time and have energy consumption requirements6. If a push-pull electromagnet wants to maintain a certain position, it needs to be continuously energized. Long-term energization may cause the coil to heat up, increase energy consumption, and may affect the service life.

Short-term action situation: When frequent actions are required in a short period of time, the energy consumption of each action of the push-pull electromagnet is relatively low, while the holding electromagnet needs to be energized every time it changes its state, and the energy consumption may be relatively high when it is frequently acted.

3.7 Control method

Control complexity: The holding electromagnet needs to change the direction of the current to control the holding and resetting of the iron core, and the control circuit is relatively complex6. The control of the push-pull electromagnet is relatively simple, and usually only the power on and off can be controlled to achieve the push and pull action.

Reliability requirements: For occasions with high control reliability requirements, if the holding electromagnet is used, it is necessary to ensure the stability and reliability of the control circuit to prevent the iron core from being unable to be held or reset normally due to control circuit failure. In some scenarios with extremely high control response speed requirements and simple control logic, the control method of the push-pull electromagnet is more advantageous.

3.8 Working environment

Temperature, humidity, etc.: Both electromagnets have their own adaptive temperature and humidity ranges, which need to be selected according to the actual working environment. Generally speaking, the holding electromagnet has a permanent magnet inside, which may demagnetize in a high temperature environment, affecting the performance, and the adaptability to the high temperature environment is relatively weak.

Vibration and shock: In an environment with vibration and shock, the permanent magnet and iron core of the holding electromagnet may become loose, shifted, etc., affecting the holding performance. If the push-pull electromagnet is well fixed, it can generally adapt to vibration and impact environments. As long as the reset parts such as springs are not damaged, it can work normally.

3.9 Cost and lifespan

Initial cost: Due to its relatively complex structure and control, the initial purchase cost of the holding electromagnet is usually high. The push-pull electromagnet has a simple structure and relatively low cost.

Service life: The service life of the holding electromagnet is affected by factors such as the performance degradation of the permanent magnet and the failure of the control circuit. If the use environment is suitable and the control is proper, its service life is also long, which can reach tens of thousands or even more than 100 million cycles1. The service life of the push-pull electromagnet is mainly affected by factors such as coil heating and spring fatigue. In the case of frequent movements, the spring may fail due to fatigue, affecting the service life.

Part four : The characteristics and disadvantages of holding electromagnets and push-pull electromagnets are as follows:

4.1 : Latching Solenoid Features

Good energy saving: No need to keep energized in the holding state, only consumes electricity when changing the state, can effectively save energy, and is suitable for scenes that need to maintain a specific state for a long time126. Stable holding force: Relying on the internal permanent magnet to generate holding force, the core can be stably held in the set position after power failure, without external interference, ensuring the stability of the equipment's working state2.

High positioning accuracy: Especially the bidirectional holding electromagnet, which can accurately hold the core in two different positions, can meet the application requirements with high position accuracy, such as precision instruments, automatic control equipment, etc.2.

Strong anti-interference ability: The magnetic field of the permanent magnet is relatively stable, and its holding performance is not easily affected by external electromagnetic interference, and it can still work reliably in a complex electromagnetic environment.

4.2 Disadvantages

Complex control circuit: It is necessary to control the holding and resetting of the core by changing the direction of the current. The control circuit design is relatively complex, which increases the cost and maintenance difficulty of the system26.

High initial cost: Due to the complexity of its structure and control, as well as the use of internal permanent magnets and other components, the manufacturing cost is high, resulting in a relatively high initial purchase price.

High environmental requirements: Permanent magnets may demagnetize in harsh environments such as high temperature and strong vibration, affecting the holding force and performance, and there are certain restrictions on the temperature, vibration and other conditions of the working environment.

Difficult to judge the state: When the power is off or the control circuit fails, it is difficult to directly judge whether the contact of the electromagnet is in the open or closed state6.

4.3 Push-pull Solelnoid Features: 

Quick action: When powered on, it can quickly generate thrust or pull force, drive the load to achieve rapid push and pull action, fast response speed, high operation frequency, suitable for occasions that require frequent action2.

Simple control: Usually, only the power on and off control can achieve push and pull action, the control logic is simple, easy to realize automatic control, the control circuit is relatively simple, and the cost is low2.

Simple structure: Generally composed of coils, iron cores and mechanical structures, the structure is relatively simple, easy to install and maintain, and can be flexibly designed and customized according to different application scenarios4.

Strong load capacity: When powered on, it can generate a large thrust or pull force, which can effectively push or pull the load. Push-pull electromagnets of different specifications can be selected according to actual needs to meet different load requirements4.

4.4 Push-pull Solelnoid  Disadvantages

High energy consumption: To maintain a certain position, continuous power supply is required. Long-term power supply will cause the coil to heat up, increase energy consumption, and may also affect the service life2.

Limited positioning accuracy: It is mainly used to complete simple push and pull actions. It is relatively poor in positioning accuracy and is not suitable for occasions with extremely high position accuracy requirements.

No power-off retention function: The position of the core cannot be maintained after power failure. It is necessary to rely on external mechanical devices or springs to achieve reset or retention. It cannot meet the requirements in some application scenarios that require power-off retention2.

Limited life: When frequent actions occur, reset components such as springs are prone to fatigue failure, which affects the service life. Long-term power-on heating of the coil may also cause problems such as insulation aging, reducing the reliability of the electromagnet.

Part Five  Summary   

5.1 :  Introduction to Solenoids

Solenoids are electromechanical devices that convert electrical energy into mechanical motion. They are used in a wide range of applications, from industrial machinery to consumer electronics.

The guide focuses on two main types: latching and push-pull solenoids, which have distinct characteristics and applications.

5.2 : Latching Solenoids

Operation Principle: Latching solenoids use a permanent magnet in combination with an electromagnet. Once energized, they can maintain their position (either latched or unlatched) without continuous power input. This makes them energy-efficient for applications where a "held" position is required for an extended period.

Advantages: They consume less power over time compared to continuously powered solenoids, which is beneficial for battery-operated devices. They also offer reliable holding force in their latched state, reducing the risk of accidental release.

Applications: Commonly used in applications such as door locks, where the lock needs to remain in the locked or unlocked position without constant power draw, and in some types of industrial control systems where maintaining a particular state is crucial.

5.3 : Push-Pull Solenoids

Operation Principle: Push-pull solenoids generate a linear force when an electric current is applied to the coil. They can either push or pull an object depending on the design and the direction of the current. When the power is removed, the solenoid returns to its initial position, usually with the help of a spring.

Advantages: They provide quick and precise linear motion, which is suitable for applications that require rapid actuation. Their relatively simple design makes them cost-effective and easy to integrate into various systems.

Applications: Found in applications like valve control in fluid systems (where they open or close valves), in automated machinery for linear movement tasks, and in some types of medical equipment for precise actuation.

5.4 : Selection Guide

Force Requirements: The guide emphasizes the importance of determining the required force for the application. Different solenoids have different force capabilities, and choosing the right one ensures proper operation.

Duty Cycle: Understanding the duty cycle (the proportion of time the solenoid is energized) is crucial. Latching solenoids may have a different duty cycle compared to push-pull solenoids, and this affects their performance and lifespan.

Size and Space Constraints: Physical dimensions of the solenoid are important, especially in applications where space is limited. The guide may discuss how to select solenoids that fit within the available space.

Voltage and Current Ratings: Matching the solenoid's voltage and current requirements with the power source in the application is essential for proper operation.

5.5 : Conclusion

The guide concludes by highlighting that choosing between latching and push-pull solenoids depends on the specific needs of the application. By carefully considering factors such as force, duty cycle, size, and electrical requirements, users can select the most appropriate solenoid option for their particular use case.

This summary provides an overview of the key points covered in a guide about latching and push-pull solenoid options, but the actual content may vary depending on the specific details in the original guide.