The solenoid valve is an electrically controlled valve. This valve is a solenoid valve that is an electric coil with a moving ferromagnetic core (piston) in the center. In the free state, the piston closes through a small hole. Electric current through the coil creates a magnetic field. The magnetic field exerts an upward force on the orifice opening piston. This is the basic principle used to open and close solenoid valves.
Important points in solenoid valves:
- Used only for clean liquids and gases.
- Indirect solenoid valves require a pressure differential to operate.
- Used to close, open, dose, separate or mix a fluid with 2 or more inlets.
- Solenoid valves have fast performance
- In the solenoid, options for manual, ATEX, gas verification, fluid separation and more.
- It can heat up because it needs energy to change and stay in that state (depending on the type).
- Compressed air, vacuum, irrigation, car wash, etc. are common in heating systems.
How does a solenoid valve work?
The solenoid valve consists of two main components: the solenoid valve and the valve body (G). The following figure shows the components. A solenoid valveIt has an electromagnetic induction coil (A) around an iron core in the center called a piston (E). At rest, it can be normally open (NO) or normally closed (NC). In the no-energy mode, an open valve is normally open and a closed valve is normally closed. When current passes through the solenoid valve, the coil receives energy and creates a magnetic field. This creates a magnetic attraction with the piston, which moves it and overcomes the spring force (D). If the valve is normally closed, the piston is removed so that the seal (F) opens the orifice and allows fluid to flow through the valve. If the valve is normally open, the piston moves downward so that the seal (F) blocks the orifice and stops the flow of media through the valve. The shading ring (C) prevents vibration and whispering in the AC windings.
Solenoid valves are used in a wide range of applications, with high or low pressures and low and high flow rates. These solenoid valves use different operating principles that are optimal for use. Three important points are described in this article: solenoid valve with direct operation, indirect operation and semi-direct operation.
Solenoid valves are used to close, open, dose, separate or mix gas or liquid streams in a pipe. The specific purpose of a solenoid valve is expressed by its function. An overview of two-way and three-way solenoid valves is given below. For a deeper understanding of symbols and performance charts, see our Lion Symbol page.
Two way solenoid valve
A two-way solenoid valve has two inlet and outlet ports. The direction of flow is very important to ensure proper operation, so there is usually an arrow that indicates the direction of flow. Two-way valve is used to open or close the hole. The following figure shows an example of a two-way solenoid valve.
Three way solenoid valve
A three-way valve has three connection ports. Typically, it has 2 modes (positions) that can be placed in it. Therefore, it switches between two different circuits. A three-way valve is used to open, close, separate or mix the fluid. The figure below shows an example of a three-way solenoid valve.
Types of solenoid valves
Normal close solenoid valve
For a normally operated solenoid valve, the valve closes when the energy is closed and fluid cannot flow through it. When current is sent to the coil, it creates an electromagnetic field that pushes the piston upwards and passes through the spring force. It does not open the seal but opens the hole and allows the fluid to flow through the valve. The following figure shows the principle of operation of a solenoid valve depending on the normal state in the state of no energy and energy.
Open normal solenoid valve
For a typical solenoid valve, the valve is open when the power is turned on and the media can flow through it. When current is sent to the coil, it creates an electromagnetic field that forces the piston to overcome the spring force. The seal is then placed in the orifice and closes, which prevents fluid from flowing through the valve. The following figure shows the principle of operation of a typical open solenoid valve in the non-energized and energetic modes. A conventional open solenoid valve is ideal for applications that require the valve to be open for a long time because it consumes less energy.
Unstable solenoid valve
An unstable or latched solenoid valve can be activated by an instantaneous power supply. Then there will be no electricity in that position. Therefore, it does not normally open or normally close in the current state, if no power is used. They do this by using permanent magnets instead of springs, and they do not switch from active to inactive until the latch operator presses.
Principles of operation of solenoid valve
Direct-acting (direct-acting) solenoid valves have a simple principle of operation, which can be seen in the figure below with the components. For a normal, non-electric close valve, the piston (E) closes the hole opening with the valve seal (F). A spring (D) performs this closure. When electricity enters the coil (A), it creates an electromagnetic field, attracts the piston upwards, and overcomes the spring force. Which opens the orifice and allows fluids to pass through it. An open valve usually has the same components, but does the opposite.
Maximum operating pressure and flow rate are directly related to the orifice diameter and magnetic force of the solenoid valve. Therefore, a direct-acting solenoid valve is typically used for relatively low flows. Direct-acting solenoid valves do not require a minimum operating pressure or pressure difference, so can be used from 0 bar to the maximum allowable pressure.
Indirect operation (or pilot) solenoid valve
Indirect solenoid valves (servo-operated or pilot-operated) use an ambient pressure differential on the inlet and outlet valves to open and close the valve. Therefore, they usually require a minimum pressure differential of about 0.5 bar. The principle of operation of a solenoid valve with indirect operation is shown in the figure below.
The inlet and outlet ports are separated by a rubber membrane, also called a diaphragm. The membrane has a small hole so that the medium can flow from the inlet to the upper chamber. For a normally closed solenoid valve that is normally closed, the inlet pressure (above the membrane) and the spring-loaded retaining spring ensure that the valve is closed. The upper chamber of the membrane is connected to the low pressure port by a small channel. This connection is blocked in the closed position by the piston and seal. The diameter of this “pilot” hole is larger than the diameter of the membrane hole. When the solenoid valve is activated, the pilot orifice opens, causing a high pressure drop in the membrane. Due to the pressure difference on both sides of the membrane, the membrane is removed and fluid can flow from the inlet to the outlet. An open valve usually has the same components, but does the opposite.
The extra pressure chamber above the membrane acts like an amplifier, so a small solenoid can still control a large flow rate. Indirect solenoid valve is used only for fluid flow in one direction. Indirect solenoid valves are used in applications with sufficient pressure differential and optimal flow rate.
Semi-direct operation solenoid valve
Semi-direct acting solenoid valves combine the properties of direct and indirect valves. This allows them to operate at zero load, but they can still have high flow rates. They look like indirect valves and also have a movable membrane with a small opening and pressure chambers on both sides. The difference is that the electric piston is connected directly to the membrane. The working principle of a semi-direct solenoid valve with direct operation is shown in the figure.
When the piston rises, it lifts the membrane directly to open the valve. At the same time, the second orifice is opened by the piston, which has a slightly larger diameter than the first orifice in the membrane. This reduces the pressure in the upper chamber of the membrane. As a result, the membrane is lifted not only by the piston but also by the pressure difference.
This combination results in valves that operate from zero loads and can control relatively high flows. Often, semi-operated direct valves have stronger windings than indirect valves. Semi-direct valves are also called lift assist valves.
Direct function three-way valve
A three-way solenoid valve has three ports, so depending on whether you want one mixing (two inputs and one outlet) or diverting (one inlet and two outputs) will affect performance. Certain valves can also work in both directions, which is called universal function. However, only two ports are connected at each location. The following figure shows an example of a three-way solenoid with direct operation.
Only two ports are connected at the same time. In the figure below, the piston has an opening at the top and bottom with two valve seats. At any given time, one is open and one is closed to route the fluid in the desired flow path. The following are examples of functions for a normally closed valve (as opposed to a typical open valve).
Three way diverting solenoid valve
The wing shape has one input (bottom left) and two outputs (top and bottom right). No power supply blocks the piston at the bottom opening, meaning that the fluid rises from the inlet to the outlet. When power is used, the piston is forced to close the top outlet. It directs this fluid from the inlet to the bottom right outlet.
Mixing three-way solenoid valve
The figure above has two inputs (top and bottom right) and one output (bottom left). No piston force blocks the lower orifice, meaning that fluid flows from the inlet to the outlet. When power is used, the piston is forced to close the top outlet. It directs this fluid from the bottom right inlet to the outlet.
Universal three-way solenoid valve
These valves act like a three-way solenoid valve. Looking at the figure above, the media can flow in both directions but only two ports are connected at a time.
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