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Insight - How Tubular Solenoid Works

Written By: 

Abhimanyu Mathur



Solenoids are a well known application where magnetic fields are used to create controlled magnetic force. Solenoids are used in various industries where they serve the purpose of hydraulic valves, current limiting switch, steering control of heavy machines etc.   This version of Insight details with DC operated tubular solenoid which is often used as an actuator. Comprising of a metallic can, coil, soft iron cored plunger along with insulator coating and connecting wires, linear solenoids are almost noiseless.


Depending upon the movement of the plunger, these solenoids can be divided into push type (where plunger goes inside the metallic can) and pull type (plunger comes out of the tin can). Tubular solenoids can work for longer hours without getting their coil overheated or burnt out.  Let’s find out what more constructional and operational features of one such tubular solenoid in this Insight. 

Tubular Solenoid

Fig. 1: Image Showing Tubular Solenoid Plunger Inside Tubular Solenoid Cavity

Image1 shows the plunger of the solenoid placed in the solenoid cavity. Made out of soft iron with nickel coat, plunger works as an actuator for the solenoid. The movement of the plunger defines solenoid to be a pull or push type. The one in the Insight is a pull one because the plunger goes inside the solenoid cavity when energized.

There are two holes in the plunger through which the load can be attached to the solenoid. In the resting state, the plunger is partially out of the metallic can and in the energized state the plunger gets attracted towards the can (due to magnetic field) and is pulled inside it.


Tubular Solenoid Shaft

Fig. 2: A Closer Look At Tubular Solenoid Plunger

External Features

Along with the plunger, two more parts are seen near it: “the nut and the lock washer”. They find their utility when solenoid is mounted on a surface or integrated with a machine.


Nut and Lockwasher

Fig. 3: 

Image Showing Various Parts of Tubular Solenoid

When the plunger, bolt and nut washer are taken out, the internal structure of the solenoid cavity is seen. A metallic container is placed on the outside and a plastic layer is placed on the inside.


Tubular Solenoid

Fig. 4: 

Connecting Wires Emerging From Sides of Tubular Solenoid

Connecting wires emerge from the other side of the solenoid. The wires are connected to the copper coil and carry current which creates a magnetic field.  So, on one end, we see the cavity, on other, wires are emerging out. Where do the wires get connected?


Opening a Tubular Solenoid

Fig. 5: 

Closer Look At The Sides of Tubular Solenoid



Tubular Solenoid Insides

Fig. 6: Image Showing Insulation Setup Inside Tubular Solenoid

The region where connecting wires disappear into the solenoid can be scooped up to take out the inner plastic layer. Copper wires are wound around the plastic bobbin which is insulated using an insulating tape.


Copper Coils

Fig. 7: How A Tubular  Solenoid Looks Post Removal of Insulation Tape

On removing the Insulating tape the copper coils of the solenoid are visible. The insulating tape is used to minimize current losses and ensure safety while handling the solenoid. It is the addition of the tape that makes the copper coil to be known as “tape wrapped coil”.  Whenever the coil is subjected to DC current, it gets magnetized, thus pulling the plunger in.


Solenoid Wiring

Fig. 8: Tubular Solenoid Copper Wires After Complete Removal of Insulation Tape

Copper Coil


Solenoid Connections

Fig. 9: 

Copper Coil


Copper Winidng

Fig. 10: Completely Unwinded Copper Coil Inside Tubular  Solenoid

In order to find what lies underneath the coil, one has to cut or unwind the coil. Beginning from where the connecting wires terminate into the coil, one can begin unwinding the solenoid. The plastic bobbin can be seen beneath the copper coils.