A solenoid spring is the component that returns the plunger and activated mechanism to its neutral position when the solenoid is deactivated. Most of the springs used are standard helical types made of tempered spring steel. Many solenoid designs position the spring around the plunger, which compresses the spring when activated. In others, it may be attached to some part of the mechanism that the solenoid is used to activate and is extended when the solenoid actuates. In all cases, however, the solenoid works against the pressure of the solenoid spring. This is true of both push and pull solenoid types.
Electric solenoids provide actuation for a wide range of mechanisms using electromagnetic force to pull a plunger into a hollow coil. The plunger movement is then harnessed to provide the required actuation force. When the solenoid is deactivated, however, the system needs to reset or return to its inactive, neutral position. This action is achieved by including a solenoid spring in the mechanism. In other words, the solenoid works against the spring's stored energy when activated. Once power to the solenoid is cut, the spring pushes or pulls the solenoid plunger and the actuated mechanism back into the neutral position.
In most cases, the solenoid spring is a common helical type. Made of tempered spring steel, this type of spring is efficient, cheap, and supplies sufficient stored energy to achieve the solenoid reset. The spring action may be either compression or extension depending on the solenoid design. For example, a pull solenoid may have the spring located around the plunger. When activated, the plunger on this type of solenoid pulls into the hollow center of the coil, compressing the solenoid spring.
Other designs may utilize a spring attached to the actuated mechanism that is extended when the solenoid activates. In rare cases, the design of the solenoid and the mechanism it actuates may require a specialist solenoid spring design such as leaf or spiral springs, making the solenoids relatively expensive to repair. Fortunately, these types of solenoids are not encountered frequently and most helical solenoid springs can be replaced from generic spring selections when worn or broken. Care should be taken, however, to ensure that the solenoid spring is replaced by one of a comparable strength. An overly-strong spring can cause the solenoid to chatter or not activate at all, while a spring that is too weak may not reset the mechanism correctly.