What is a Solenoid Valve?

Solenoid valve

A solenoid valve is one of the common kinds of electromagnetic valves. They are used to convert electrical energy into mechanical energy and are unique in appearance.

As you can see in Figure 1 below, the body of the solenoid valve is the bottom part, while the top features a block, from which cables extend when the valve is installed That top part is the solenoid, which consists of fixing tendons, coils, and plungers. Solenoid valves use a steel tendon to become a magnet when electricity is supplied to the coil inside the solenoid.

Why use a Solenoid Valve?

Solenoid valves allow engineers to autonomously and remotely control the flow of fluid within a system. This fluid can be a liquid or gas (water, air, oil, steam, and so on). 

How Do Solenoid Valves work?

The solenoid coil on the top is used to operate the valve by passing an electrical current through the coil to create an electromagnetic field to operate the valve, which means it can be operated autonomously and remotely by a computer without the need for to the valve to be manually opened and closed. For example, in industrial settings, factories can use solenoid valves to pour sodas in a production line. Solenoid valves can also be used to detect and prevent leaks from the pipes. If there is leakage in the pipe, the controller will send a signal to close the valve from which the leak originated. 

Solenoid structure

There are several types of solenoid valves, but the plunger type is the most popular. A plunger is used along the axis inside the coil, and the plunger itself is classified into T-and I-types. 

  • T-type plungers can increase a solenoid’s magnetism and stroke, but it is larger in size and consumes more power. Therefore, a T-type plunger is suitable for a slide valve that requires a long stroke to open and close the valve or a direct spool valve that requires a relatively large force. 
  • I-type plungers have a lower magnetism and a shorter stroke compared to T-type plungers, but a driving tendon can be installed directly in the valve body to minimize the size of the valve. Therefore, I-type plungers are mostly used in direct type poppet or pilot type valves. 
Solenoid valve
Figure. 1 Structure of solenoid

Solenoid Power

Solenoids can be classified into direct current (DC) and alternating current (AC) types, according to the type of power supply. 

A DC solenoid has the following characteristics:

  • There is no loss of current, so it has a low temperature increase. 
  • Because the field current remains consistent across the stroke, the coil is not damaged by excess current. 

An AC type solenoid uses ordinary power and does not need an AC-to-DC converter. It ensures a stable response, though it makes a little noise from time to time as the voltage and electric current change. 

Following are the characteristic of AC type solenoid: 

  • The components of the power circuit are easy to find and cost effective. 
  • Power consumption increases when there is a magnetic force, but it reduces afterward to save overall power consumption.

Characteristics of a Solenoid 

Solenoids have the following characteristics:

Characteristics of Magnetism

Magnetism occurs when electricity is supplied to the coil part of the solenoid. Both AC solenoid and DC solenoid have similar magnetism. In order to convert the valve body by flowing electricity through the coil of the solenoid, the magnetism must be larger than the exertion of the spring or spring force. For normal operation of the solenoid valve, the magnetism must be larger than the spring force, even with minimum voltage. When power is disconnected and the valve body is returned by the spring, the valve will not return if the solenoid’s magnetism. The spring force must be larger than the valve’s magnetism for the valve to return to its original position. 

Current Characteristics

AC and DC solenoids have different characteristics. AC solenoids have a long stroke plunger and require a lot of electric current to move through the stroke. As the plunger moves and shortens the stroke, the required amount of electrical current reduces. When the plunger attaches to a fixed tendon, the amount of current minimizes to consume a certain amount of residual current (holding current). In the case of a DC solenoid, the electrical and holding currents remain consistent, regardless of changes in stroke. The DC solenoid is made to prevent the transmission of electric force, even when the electric current continuously suppled with the plunger is already in place. On the other hand, an AC solenoid can have a damaged coil because of excess current when the difference in electrical current and holding current is large and attracts impurities to the valve body, making it impossible for a solenoid to attach to it. An AC solenoid with a long stroke and low magnetism, on the other hand, hardly experiences such damage. Also, a DC solenoid is well protected from a damaged coil for the same reason. 

Frequency Characteristics

Alternating current uses 50 or 60 [Hz] frequency. The characteristics of an AC solenoid vary according to frequency, but a small solenoid is generally designed to use both 50 and 60 [Hz] frequencies. A large solenoid with high magnetism has different frequency characteristics and requires the use of a designated coil or a coil with an individual terminal based on select frequency. Also, an AC solenoid generates noise because the frequency of magnetism fluctuates with the fluctuation of frequency. To reduce the noise, it is necessary to insert a patterned coil on the magnetic surface of the solenoid.

Temperature Characteristics

When electricity is supplied to the coil in the solenoid, heat is generated, and the temperature of the coil rises. After some time passes, heat generation and heat release find a middle ground, and the coil maintains a certain temperature, which is called “temperature increment.”

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