Basic knowledge of solenoid valve: principle, maintenance, selection
Solenoid valve is an electromagnetic control industrial equipment, in the industrial control system to adjust the direction of the medium, flow, speed and other parameters. According to the characteristics of the solenoid valve, how should the solenoid valve be selected? In order to extend the life of the solenoid valve, how to maintain it?
Interpretation | Structural principle of solenoid valve
(1. Valve body 2. Air inlet 3. Air outlet 4. Wire 5. Plunger)
After looking at the dynamic diagram, did you find that the working principle of the solenoid valve is very simple! When the solenoid valve is not powered on, the valve needle gambles the channel of the valve body under the action of the spring, and the solenoid valve is in the off state. When the power of the coil is turned on, the coil generates magnetic force. The core of the valve is lifted up against the spring force. The Inner channel of the valve is opened and the solenoid valve is in the state of conduction.
Simple, solenoid valves are divided into three categories
The principle of solenoid valve is divided into three categories: direct-operated type, step-by-step direct-operated type and pilot-operated type.
Now I have made a summary from three aspects: Introduction, principle and characteristics.
Direct-acting solenoid valve
There are two types of normally closed type and normally open type. When the normally closed type is off, it is in the closed state. When the coil is on, electromagnetic force is generated, which makes the moving iron core to overcome the spring force and the static iron core open the valve directly, and the medium is in the Channel; When the coil is off, the moving iron core is reset under the action of spring force, and the valve mouth is directly closed, and the medium is impassable. The structure is simple, the action is reliable, and it works normally under zero pressure difference and micro vacuum. The normally open type is just the opposite. For example, the solenoid valve with the flow diameter less than φ6.
When the normally closed type is energized, the electromagnetic force generated by the electromagnetic coil lifts the open piece from the valve seat and the valve opens; When the power is off, the electromagnetic force disappears and the spring presses the open piece on the valve seat and the valve opens. Normally open type opposite this)
It can work normally in vacuum, negative pressure and zero pressure, but the diameter is generally not more than 25mm.
Step-by-step direct-acting solenoid valve
This kind of valve adopts one-time valve opening and two-time valve opening connected to one main valve and guide valve to directly open the main valve by electromagnetic force and differential pressure. When the coil is power-on, electromagnetic force is generated to make the moving iron core and static iron core come together, the guide valve is opened and the guide valve is set at the main valve port, and the moving iron core is connected with the main valve core, at this time, the pressure of the main valve cavity is unloaded through the guide valve port, and under the simultaneous action of pressure difference and electromagnetic force, the main valve core moves upward and the main valve is circulated in medium. When the power of the coil is off, the electromagnetic force disappears. At this time, the moving iron core closes the pilot valve hole under the action of self-weight and spring force. At this time, the medium enters the upper cavity of the main valve core in the balance hole to increase the pressure in, at this time, under the action of Spring Reset and pressure, close the main valve and medium cut-off. The structure is reasonable, the action is reliable, and the work is reliable at zero pressure difference. Such as: ZQDF,ZS,2W, etc.
It is a kind of principle of the combination of direct action and pilot action. When there is no differential pressure between the inlet and the outlet, after being energized, the electromagnetic force directly raises the closing pieces of the pilot small valve and the main valve in turn, valve open. When the start differential pressure of the inlet and the outlet reaches, after electrifying, the electromagnetic force leads to a small valve, the pressure in the inferior space of the main valve rises, and the pressure in the superior space drops, thus pushing the main valve upward by the use of differential pressure; When, the pilot valve uses spring force or medium pressure to push the closing piece and move downward to close the valve.
It can also be operated in zero pressure difference or vacuum and high pressure, but the power is large and it is required to be installed horizontally.
Indirect guide solenoid valve
This kind of solenoid valve consists of the channel formed by connecting the pilot valve and the main valve core; The normally closed type is in the closed state when it is not energized. When the coil is power-on, the generated magnetic force makes the iron core and the static iron core fit together. When the guide valve port opens the medium flow outlet, the pressure of the main valve core cavity reduces at this time, which is lower than the pressure of the inlet side, forming a pressure difference to overcome the spring resistance and move upward to achieve the purpose of opening the main valve port, medium flow. When the power of the coil is off, the magnetic force disappears, and the movable iron core resets and closes the pilot port under the action of the spring force. At this time, the medium flows in from the balance hole, and the pressure of the upper cavity of the main valve core increases, and under the action of spring force to move downward, close the main valve port. The normally open principle is just the opposite.
When electrifying, the electromagnetism force will open the pilot hole, so that the pressure of the upper chamber will drop rapidly. A high differential pressure will be formed around the open part, and the fluid pressure will push the open part to move the valve upward to open; When the power is off, the spring force opens the pilot hole, and the inlet pressure forms a lower, higher and higher pressure difference around the closing valve through the via-hole rapid chamber. The fluid pressure drives the open piece to move downward and opens the valve.
Small volume, low power, high upper limit of fluid pressure range, can be installed arbitrarily (customized) but must meet the condition of fluid pressure difference.
Instructions | Analysis of Solenoid Valve characteristics
External leakage is blocked, internal leakage is easy to control, and it is safe to use.
Internal and external leakage is a safety hazard. Other self-control valves usually stretch out the valve rod, and the running or moving of the valve element is controlled by electric, pneumatic and hydraulic actuators. This is to solve the problem of external leakage of the dynamic seal of the valve stem with long-term action. Only the solenoid valve uses magnetic force to act on the iron core sealed in the magnetic isolation casing. There is no dynamic seal, so the external leakage is easy to plug. The torque control of the electric valve is not easy, and it is easy to generate internal leakage, and even pull off the head of the valve rod; The structure type of the solenoid valve is easy to control internal leakage until it drops to zero. Therefore, the solenoid valve is particularly safe to use, especially suitable for corrosive, toxic or high and low temperature Media.
The system is simple, and the price is low.
The solenoid valve itself is simple in structure and low in price, which is easier to install and maintain than other types of actuators such as regulating valves. What is more obvious is that the automatic control system is much simpler and the price is much lower. Since the solenoid valve is controlled by switch signal, it is very convenient to connect with industrial control computer. In today’s computer popularization, the price of the sharp decline in the era, the advantages of the solenoid valve is more obvious.
The action power is small and the appearance is lightweight.
The response time of the solenoid valve can be as short as a few milliseconds, and even the pilot solenoid valve can be controlled within tens of milliseconds. Due to the self-formed circuit, it is more sensitive than other self-control valves. The power consumption of the properly-designed electromagnetic valve coil is very low, and it is an energy-saving product; It can also be achieved that only trigger the action and automatically maintain the valve position, and usually do not consume electricity at all. The outer size of the solenoid valve is small, which not only saves space, but also is light and beautiful.
Limited adjustment precision and limited applicable medium.
The solenoid valve usually has only two states of switch. The spool can only be in two limit positions and cannot be continuously adjusted. (there are a lot of new ideas trying to break through, but they are still in the Test trial stage) therefore, the adjustment accuracy is still limited. The solenoid valve has a higher requirement for the cleanliness of the media, and the media containing particles are not applicable. If it is an impurity, it must be filtered first. In addition, viscous media cannot be applied, and the range of media viscosity applicable to specific products is relatively narrow.
Various models and wide uses.
Although the solenoid valve has congenital deficiencies, its advantages are still very prominent, so it is designed into a variety of products to meet various needs and has a very wide range of uses. The progress of solenoid valve technology also focuses on how to overcome the congenital deficiencies and how to better play the inherent advantages.
Hot spot | Solenoid valve selection
There are many solenoid valves that can be used universally, and the most economical products should be selected during the selection process.
General solenoid valve is not waterproof, please choose waterproof type when conditions are not allowed, the factory can be customized. The maximum nominal pressure of the solenoid valve must exceed the maximum pressure in the pipeline, otherwise the service life will be shortened or other unexpected situations will occur.
Corrosive liquid should use all stainless steel type, strong corrosive fluid should use plastic King (SLF) solenoid valve. The corresponding explosion-proof products must be used for the explosive environment.
The solenoid valve is divided into normally closed and normally open; Generally, the normally closed type is selected, and the power is turned on and off. However, when the opening time is very long and the closing time is very short, the normally open type should be selected.
Life test, the factory generally belongs to the type test project, to be exact, china does not have a professional standard for solenoid valves, so the choice of solenoid valve manufacturers with caution. The action time is very short, and the frequency is high. Generally, the direct-type large diameter is selected as the fast series.
The fluid in the pipeline must be consistent with the media labeled in the selected solenoid valve series model. The temperature of the fluid must be lower than the calibration temperature of the solenoid valve. The magnetic valve allows the viscosity of the liquid to be generally below 20CST, which should be indicated when it is greater than 20CST.
When the working pressure difference and the maximum pressure difference of the pipeline is less than 0.04MPa, it should use straight-line type and step-by-step straight-line type such as ZS ,2W,ZQDF,ZCM series. If the minimum operating differential pressure is greater than 0.04MPa, pilot-operated (differential pressure) solenoid valve can be selected. The maximum operating differential pressure should be less than the maximum calibration pressure of the solenoid valve.
The general solenoid valve is one-way work, so pay attention to whether there is an inverse pressure difference, such as the installation of the check valve.
When the fluid cleanliness level is not high, the filter should be installed in front of the solenoid valve. Generally, the solenoid valve should require better cleanliness level for the media. Pay attention to the flow aperture and the caliber of the connecting pipe. The solenoid valve is generally only allowed by the two control conditions of the switch. Please install the bypass pipe for maintenance. If there is a water hammer, customize the opening and closing time adjustment of the solenoid valve.
Notice the influence of the environment temperature on the solenoid valve supply current and power consumption should be selected according to the output capacity the supply voltage is generally allowed around ± 10%, and attention must be paid to the higher VA value when the ac starts.
Attention | Solenoid valve maintenance
- Note 1: pilot solenoid valve, to check whether the pressure difference in the pipeline is too small, the pressure difference is too small solenoid valve can not work normally, in this case, you need to choose the direct-acting solenoid valve. However, the pressure difference is too large to exceed the design value of the solenoid valve and cannot work normally, so high-pressure solenoid valve should be selected.
- Note 2: the solenoid valve is generally installed horizontally. If the pepper is installed on the side, it may cause the valve to close slowly, that is, internal leakage, because try to avoid side installation.
- Note 3: when the service time is long, if the sealing between the piston and the valve seat is not good, the piston sealing surface can be flattened again, and then grinded with the valve seat.
- Note 4: when working, pay attention to the pressure gauge before and after the valve, the working pressure must not exceed the rated pressure, and the working pressure difference must be within the rated pressure difference range. When the working pressure exceeds the rated pressure or the working pressure difference exceeds the rated pressure difference, the solenoid valve should be stopped and the front and rear manual valves should be closed to prevent the solenoid valve from exploding and leaking.
- Note 5: after the solenoid valve is installed, it must be introduced into the media for several times to test the action, and it can be put into formal use after confirming normal.
- Note 6: the dirt on the inside and outside of the large valve and the surface of the armature should be cleaned regularly. Be careful not to damage the sealing surface.
- Note 7: when the solenoid valve is not in use for a long time, the valve should be closed before the manual valve, when it is re-started, the steam solenoid valve should be drained out the condensate water, and test the action for several times, and put into use after the switch is normal.
Source: China Solenoid Valve Manufacturer– Yaang Pipe Industry Co., Limited (www.steeljrv.com)
(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)
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