The solenoid usually install in the solenoid valve for controlling air, fluid and pressure. Solenoid is used to handle paths and it can be removed from the valve. How does a solenoid work? When solenoid is powered, it will create electromagnetic force and attracts moveable core. Once power is interrupted, magnetic field will disappear and moveable core will reset. Solenoid operated hydraulic valves are commonly based on this principle of work. solenoid have wide applications like solenoid for ON-off hydraulic valve, solenoid for proportional valve, solenoid for explosion-proof valve, etc.

Solenoid classifications

Solenoid is an inductor, it refers to every wire was screwed up and insulated with each other. Core tube of solenoid can be hollow, or iron core or magnetic powder core included. So solenoid also called solenoid coil sometimes. There are following parameters for solenoid:

  • L for inductance value that is an inherent characteristic of solenoid, but nothing on electric current. Except special solenoid, there is usually no label on common solenoid, but inductance value will be labeled with other names.
  • XL for inductive reactance is the interaction between current and solenoid coil. Unit of inductive reactance is Ohm. Formula for inductance value, inductive reactance and AC frequency is XL=2π
  • Q for quality factor refers to solenoid quality. Q is ratio of XL to equivalent resistance: Q=XL/R. In general, value of Q for solenoid is higher, loss of loop is smaller. Q value of solenoid is related to some elements, such as direct current resistance of wire, dielectric loss of framework, loss of shield or iron core, high frequency skin effects, etc. Q value of solenoid is in a range of tens to hundreds.
  • Distributed capacitance is a capacitance between turns, or coil and shield, or solenoid coil and plates. Distributed capacitance will reduce the Q value of solenoid coil, which has effect on stability of solenoid coil. So that for distributed capacitance, the smaller the better.

Single layer solenoid coil

Single layer solenoid coil is that insulated wires are wound around paper tube or bakelite framework. Typical applications include transistor radio.

Lattice coil

Coil of lattice coil don’t parallel to surface of revolution, but intersect at certain angle. The advantages of lattice coil include small size, Small distributed capacitance and large inductance value. Lattice coil is generally made by honeycomb winding machine.

Ferrite cored coil and compressed-iron-core coil

The inductance value of solenoid is related to iron core. Add iron core into hollow solenoid coil can increase inductance value and improve the quality of solenoid coil.

Copper core coil

Copper core coil is mostly applied in the short wavelength. Copper core coil mainly rotate position of cooper core to change the inductance value, which is an easy and durable adjustment.

Inductor with color codes

Inductor with color codes is a kind of inductor with fixed inductance value. Inductance value is marked with color ring like resistance.

Choking coil

Choking coil stop the alternating current, it can be divided into high-frequency choke and low-frequency choke.

Deflection coil

Deflection coil is made up of a pair of horizontal coil and a pair of vertical coil. A qualified deflection coil has advantages of high deflection sensitivity, uniform magnetic field, high Q value, small size, etc.

Solenoid function

Once Moveable core of solenoid is powered, it will be attracted with coil. Conducting and on-conducting state of valve will be controlled by movement of iron core. Dry or wet type refers to the coils’ work environment. But a hollow solenoid coil is different with a solenoid is made up of coil and iron core. Solenoid produces higher inductance value than solenoid coil.

Solenoid test

  1. Use the multimeter to measure electric resistance of solenoid operated valve, the standard value is about 100 Ohm. If the resistance of solenoid is infinity, which proved that the solenoid is broken.
  2. Make solenoid powered and put iron object on the solenoid, at this moment, solenoid is magnetic. If solenoid can attract iron object, which shows that solenoid is qualitied.

What is the reason for overheated solenoid?

Overheated problem of solenoid has influence on solenoid’s service life. What is the reason foe overheated solenoid? When solenoid is on-state and moveable core is attracted, which come a closed magnetic circuit. Under largest inductance value, heating of solenoid is normal. Overheated solenoid is caused by a lot of elements, for example, when iron core can’t be attracted smoothly, inductance value decrease, impedance decrease, current increase. So oil stain easily cause overheated problem.