1、 Working principle of solenoid valve - Introduction

Electromagnetic valve, also known as Electromagnetic value in English, is an automated basic component used to control fluids. It is commonly used in industrial control systems to adjust parameters such as direction, flow rate, and velocity of media. Electromagnetic valves have the characteristics of high precision, good flexibility, multiple models, and wide applications. Electromagnetic valves can be divided into various types, and different electromagnetic valves can play their roles in different positions of the control system.

2、 Working principle of solenoid valve

There is a sealed chamber inside the solenoid valve, with a piston in the middle and two electromagnets on both sides of the chamber. Once the electromagnetic coil is energized, the valve body is attracted to the direction of the energized electromagnet by force; And there are through holes at different positions in the chamber, connecting different oil pipes, so the part of the oil discharge hole can be selected to be opened by controlling the movement of the valve body; Due to the oil inlet being in a normally open state, the movement of the valve body allows hydraulic oil to enter different oil discharge pipes. The pressure of the oil pushes the piston of the cylinder, which in turn pushes the piston rod, thereby driving the mechanical device. By utilizing this principle, it is possible to achieve the function of controlling mechanical motion by controlling the on/off of electromagnetic current.

3、 Working principle of solenoid valve - classification

Electromagnetic valves can be classified into various types based on their functions, such as water solenoid valves, high-pressure solenoid valves, fire solenoid valves, etc. They can also be classified into six types based on valve structure, materials, etc.: direct acting diaphragm structure, pilot diaphragm structure, distributed direct acting piston structure, etc. However, the most important classification method for solenoid valves is based on their principles, which can be divided into three types: direct acting solenoid valves, step-by-step direct acting solenoid valves, and pilot operated solenoid valves. Next, let's take a look at the differences in the principles of these three types of solenoid valves?

4、 Working principle of solenoid valve - direct acting solenoid valve

When the direct acting solenoid valve is powered on, it generates magnetic force through the electromagnetic coil to lift the closing member from the valve seat and open the valve, controlling the movement of the mechanical device; When the power is cut off, the electromagnetic force disappears, and the closing member is re pressed against the valve seat by the spring, causing the valve to close.

5、 Working principle of solenoid valve - pilot operated solenoid valve

When the pilot operated solenoid valve is powered on, the electromagnetic coil generates electromagnetic force to open the pilot hole, causing a sharp drop in pressure in the upper chamber and creating a high pressure difference between the upper and lower parts at the closing part. As a result, the closing part is pushed upward by pressure, and the valve is opened; When the power is cut off, the electromagnetic force disappears, and the pilot hole closes under the action of the spring, forming a pressure difference of high and low at the closing part, which then pushes the closing part downwards and closes the valve.

6、 Working principle of solenoid valve - step-by-step direct acting solenoid valve

The step-by-step direct acting solenoid valve combines the working principles of direct acting and pilot operated solenoid valve switches. When there is no pressure difference at the inlet and outlet or the pressure difference is small enough to push the valve to move, the valve is opened by the action of electromagnetic force (similar to the direct acting solenoid valve); When the pressure difference between the inlet and outlet can push the valve to move, use the pressure to open the valve (similar to a pilot operated solenoid valve); After power failure, when there is no pressure difference or electromagnetic force, the valve closes under the action of the spring.

In summary, the working principle of solenoid valves is to control the valve opening and closing by controlling the power on and off of the solenoid coil, thereby controlling the movement of the mechanical device. The difference in the working principle of the three types of solenoid valves lies in the different ways in which the solenoid coil opens and closes the valve.

There are many factors that affect the service life of solenoid valve products, and corrosion of solenoid valves is one of the important influencing factors. Extending the service life of solenoid valves, improving project safety, and anti-corrosion of solenoid valves are important considerations. How to effectively protect solenoid valve products, and what are the precautions in purchasing? You need to know the following methods.

Select corrosion-resistant materials based on the type of medium

In practical production applications, solenoid valves face a variety of media types, and even for the same medium, the corrosion rate of materials varies under different pressures, temperatures, and concentrations. For example, aluminum is highly corrosive in concentrated nitric acid with a concentration of over 80%, but its corrosion is not severe in medium to low concentrations of nitric acid. Carbon steel is most severely corroded in sulfuric acid with a concentration of 50%, and when the concentration reaches over 90%, the corrosion sharply decreases. So, when purchasing solenoid valve products, you can analyze the type of medium and the degree of corrosion of materials by different concentrations of media, or consult the manufacturer directly.

Select corrosion-resistant solenoid valves

Corrosion resistant solenoid valves are solutions specifically designed for corrosive media. Many corrosion-resistant solenoid valves use non-metallic materials as the contact surface between the solenoid valve cavity and the media. Materials such as natural rubber and polytetrafluoroethylene not only have good corrosion resistance, but also play a role in saving precious metals as long as the pressure and temperature of the project environment meet the characteristics of the materials.

Surface treatment of solenoid valve

The surface treatment of solenoid valves can be divided into thermal spraying and spray coating. Thermal spraying is one of the techniques for adding a protective layer to the surface of equipment. Thermal spraying is the use of high energy density heat sources, such as gas combustion flames, electric arcs, plasma arcs, electric heating, gas explosions, etc., to heat and melt metal or non-metal materials, and then spray them onto the pre treated basic surface in the form of atomization to form a spray coating. Thermal spraying can improve the corrosion resistance, wear resistance, high temperature resistance and other characteristics of the surface of solenoid valves, extending the service life of products.

Spray coating is a common method, which belongs to non-metallic materials. When applied to metal surfaces or cavities, it can effectively isolate the medium and atmosphere, achieving the purpose of corrosion prevention.

Control corrosive environment

Controlling the corrosive environment is mainly aimed at the working environment where the solenoid valve is located, such as effectively controlling dust, water vapor, smoke, and toxic gases in the environment to maintain cleanliness and dryness.

Electromagnetic valves are widely used in our production. Let's first have a preliminary understanding of electromagnetic valves. Electromagnetic valves are composed of electromagnetic coils and magnetic cores, and are valve bodies containing one or several holes. When the coil is powered on or off, the operation of the magnetic core will cause the fluid to pass through the valve body or be cut off, in order to change the direction of the fluid. The electromagnetic components of the solenoid valve consist of a fixed iron core, a moving iron core, coils, and other components; The valve body is composed of slide valve core, slide valve sleeve, spring base, etc. The electromagnetic coil is directly installed on the valve body, which is enclosed in a sealed tube, forming a simple and compact combination. The solenoid valves we commonly use in production include two position three-way, two position four-way, two position five way, etc. Let's first talk about the meanings of the two: for solenoid valves, it means being energized or de energized, and for the valves being controlled, it means being open or closed.

It consists of valve body, valve cover, electromagnetic components, spring, and sealing structure. The sealing block at the bottom of the moving iron core closes the valve body inlet with the pressure of the spring. After being powered on, the electromagnet is attracted, and the sealing block with a spring on the upper part of the moving iron core closes the exhaust port. The airflow enters the membrane head from the intake port, playing a controlling role. When the power is lost, the electromagnetic force disappears, and the moving iron core leaves the fixed iron core under the action of the spring force, moves downward, opens the exhaust port, blocks the intake port, and the diaphragm head air flows through the exhaust port to be discharged, and the diaphragm returns to its original position. In our oxygen production equipment, there are applications such as emergency shut-off of the membrane regulating valve at the inlet of the turbine expander

When current passes through the coil, excitation is generated, and the fixed iron core attracts the moving iron core. The moving iron core drives the slide valve core and compresses the spring, changing the position of the slide valve core and thus changing the direction of the fluid. When the coil loses power, the slide valve core is pushed by the elastic force of the spring, pushing the iron core back and forth, causing the fluid to flow in the original direction. In our oxygen production, the switch of the forced valve of the molecular sieve switching system is controlled by a two position four-way solenoid valve, and the airflow is supplied to both ends of the piston of the forced valve. So as to control the opening and closing of the forced valve.

As an actuator of automation instruments, solenoid valves have seen a sharp increase in usage in recent years. This article analyzes the main characteristics of solenoid valves and provides a brief overview of the development trends of mature technologies in China from an application perspective. It examines the directions of simplification, intelligence, generalization, and specialization, and briefly discusses the social factors that affect the development of solenoid valve technology.

1、 The main characteristics of solenoid valves

(1) The system is simple, easy to connect to a computer, and the price is affordable. The solenoid valve itself has a simple structure and low price, making it easier to install and maintain compared to other types of actuators such as regulating valves. More significantly, the composed self-control system is much simpler and priced much lower. Due to the fact that the solenoid valve is controlled by switch signals, it is very convenient to connect with industrial control computers. In today's era of widespread computer use and significant price reductions, the advantages of solenoid valves are even more apparent.

(2) External leakage is blocked, internal leakage is easy to control, and safe to use. Internal and external leakage is a factor that endangers safety. Other self-control valves usually extend the valve stem and control the rotation or movement of the valve core through electric, pneumatic, or hydraulic actuators. All of this needs to solve the problem of long-term leakage of valve stem seals; Only solenoid valves use electromagnetic force to seal the iron core inside the magnetic isolation sleeve, without dynamic sealing, so external leakage is easily blocked. Electric valve torque control is not easy, which can easily cause internal leakage and even break the valve stem head; The structural type of solenoid valve is easy to control internal leakage until it is reduced to zero. So, the use of solenoid valves is particularly safe, especially suitable for corrosive, toxic, or high and low temperature media.

(3) Action express, with minimal power and lightweight appearance. The response time of solenoid valves can be as short as a few milliseconds, and even pilot operated solenoid valves can be controlled within tens of milliseconds. Due to its self-contained circuit, it responds more sensitively than other self-control valves. A well-designed solenoid valve coil has low power consumption and is considered an energy-saving product; It can also automatically maintain the valve position by triggering the action, without consuming any electricity during normal operation. The electromagnetic valve has a small external size, which saves space and is lightweight and beautiful.

(4) Diverse models and versatile applications. Although solenoid valves have inherent shortcomings, their advantages are still very prominent, so they are designed into a variety of products to meet different needs and have a wide range of applications. The progress of solenoid valve technology also revolves around how to overcome inherent shortcomings and better leverage inherent advantages.

(5) The adjustment accuracy is limited and the applicable medium is restricted. Electromagnetic valves usually have only two states: on/off, and the valve core can only be in two extreme positions, which cannot be continuously adjusted. (There are many new ideas trying to break through, but they are still in the experimental stage) Therefore, the adjustment accuracy is still limited to a certain extent. Electromagnetic valves have high requirements for the cleanliness of the medium, and are not suitable for media containing particles. If impurities are present, they must be filtered out first. In addition, viscous media are not suitable, and the viscosity range of media suitable for specific products is relatively narrow.

2、 Introduction to the Development of Electromagnetic Valve Technology More Electromagnetic Valve Technology

The development of the direction of refinement and simplification is essential, and only simplicity can be passed down for a long time. This is also the eternal pursuit of scientists and engineers.

(1) Simplify the control circuit. Previous actuators extensively used pneumatic and electric control circuits, which increased the complexity of the system. Pilot operated solenoid valves, on the other hand, form a control circuit inside the valve that utilizes the working medium itself, with a very simple structure. In the past, multiple technical parameters of solenoid valves at home and abroad were still limited, but now the diameter of solenoid valves in China has been expanded to 300000 mm; The medium temperature ranges from -200 ℃ to 450 ℃; The working pressure ranges from vacuum to 25MPa. The action time ranges from tens of seconds to a few milliseconds. The new development of these technologies can completely replace the bulky and expensive two position control quick shut-off valves, pneumatic switch valves, electric switch valves, and partially replace continuous adjustment pneumatic and electric control valves. (How to better meet the requirements of adjustment accuracy, which will be discussed in the following text). Foreign industries such as textiles, light industry, and urban construction have extensively adopted solenoid valves, while metallurgical and chemical industries have taken the lead in using more and more solenoid valves in auxiliary systems.

Domestic automation professionals are increasingly paying attention to solenoid valves.

(2) When simplifying the operation of the automatic control valve in the pipeline system, some auxiliary valves and fittings must also be equipped on the pipeline. This piping system takes up a large amount of space, is time-consuming to install, and is prone to leakage. The ZDF series multifunctional solenoid valve cleverly eliminates these additional accessories and still has the function of isolating bypass, thus winning the Geneva International New Technology Gold Award. A filter needs to be installed in front of the automatic control valve. When multiple self-control valves are used in combination, it is often necessary to install one-way valves to prevent interference between pipelines. Now, one-way solenoid valves, combination solenoid valves, and filtered solenoid valves have all played a role in simplifying pipelines.

1、 Characteristics of solenoid valve

1. Choose different types of solenoid valves for gas, liquid or mixed states, such as ZQDF for air, ZQDF-Y for liquid, ZQDF-2 (or -3) for steam, otherwise it may cause misoperation. The ZDF series multifunctional solenoid valve can be connected to air Liquid. It is best to inform the media status when booking, so that the installation user does not need to adjust it again.

2. Products with different specifications and medium temperatures may cause the coil to burn out and the seals to age, seriously affecting their lifespan.

3. The viscosity of the medium is usually below 50cSt. If the diameter exceeds 15mm, use the ZDF series multifunctional solenoid valve for special ordering. High viscosity solenoid valve with a diameter less than 15mm.

4. When the cleanliness of the medium is not high, a backwash filter valve should be installed in front of the solenoid valve. When the pressure is low, a direct acting diaphragm solenoid valve such as CD-P can be used.

5. If the medium flows in a directional manner and does not allow reverse flow, ZDF-N and ZQDF-N need to flow in both directions. Please make special requirements. The temperature of the medium should be selected within the allowable range of the solenoid valve.

2、 Pipeline parameters

1. Select valve ports and models based on the requirements of medium flow direction and pipeline connection method. For example, for switching from one pipeline to two pipelines, CA5 and Z3F are selected for small diameters, and ZDF-Z1/2 is selected for medium or large diameters. For controlling the convergence of two pipelines, please choose ZDF-Z2/1, etc.

2. Select the nominal diameter based on the flow rate and valve Kv value, or choose the same pipe inner diameter. Please note that some manufacturers do not indicate the Kv value, and the valve hole size is often smaller than the interface pipe diameter. Do not be tempted by low prices and make mistakes.

3. Work pressure difference. Indirect pilot type can be used when the minimum working pressure difference is above 0.04Mpa; For those with a minimum working pressure difference close to or less than zero, direct acting or step-by-step direct acting must be selected.

3、 Environmental conditions

1. The maximum and minimum temperatures of the environment should be selected within the allowable range. If there is any deviation, special orders should be made.

2. In environments with high relative humidity and water droplets and rain, waterproof solenoid valves should be selected.

3. Special types such as marine solenoid valves should be selected for situations where there are frequent vibrations, bumps, and impacts in the environment.

4. When used in corrosive or explosive environments, priority should be given to selecting corrosion-resistant materials based on safety requirements.

5. If the environmental space is limited, please choose a multifunctional solenoid valve as it eliminates the need for a bypass and three manual valves, and is easy to maintain online.

1. Switch form:

The solenoid valve is driven by a coil and can only be turned on or off, with a short action time when turned on or off.

The driving of electric valves is usually done by motors, and the opening or closing action requires a certain amount of time for analog measurement, which can be adjusted.

2. Job nature:

Electromagnetic valves generally have a small flow coefficient and a small working pressure difference. For example, the flow coefficient of a typical 25 caliber solenoid valve is much smaller than that of a 15 caliber electric ball valve. The drive of solenoid valves is through electromagnetic coils, which are relatively easy to be damaged by voltage surges. Equivalent to the function of a switch, it has two functions: on and off.

Electric valves are generally driven by motors, which are more resistant to voltage surges. Electromagnetic valves are quick opening and quick closing, generally used in places with low flow and low pressure, requiring high switching frequency. Electric valves are the opposite. The opening of the electric valve can be controlled, with states including open, closed, and half open/half closed, which can control the flow rate of the medium in the pipeline. However, the solenoid valve cannot meet this requirement.

Electromagnetic valves can generally reset when powered off, while electric valves require a reset device for this function.

3. Applicable process:

Electromagnetic valves are suitable for some special process requirements, such as leakage, special fluid media, etc., and are relatively expensive.

Electric valves are generally used for regulation, and there are also switch quantities, such as at the end of fan coil units.