Yonglong explains the purpose of correctly selecting the type of electric valve
Time: August 18, 2020 13:23:06 Source: Yonglong Valve Reading: zero second
Yonglong explains the purpose of correctly selecting the type of electric valve
YongLong purpose on the correct selection of electric valve type
In the application of mechanical equipment and pipeline engineering, the correct selection of electric valve type is one of the guarantee conditions to meet the use requirements. If the electric valve used is not properly selected, it will not only affect the use, but also may bring adverse consequences. So, how do we use the electric valve correctly? Listen to the Electric control valve editor of Yonglong Valve to explain:
1、 What is an electric valve?
Electric valve is simply a valve driven and controlled by electric actuator with power supply, so as to open and close the valve. It can be divided into two parts, the upper part is the electric actuator, and the lower part is the valve. It can also be called Electric shut-off valve 。
General electric valves include: electric cut off valve, electric ball valve, electric stop valve, electric butterfly valve, electric gate valve, electric regulating valve, electric diaphragm valve, electric cock valve, Electric liquid ammonia cut off valve, electric emergency shut off valve and other products.
Electric valve is a product of automatic control valve. It can not only realize the switch function, but also realize the valve position adjustment function of regulating electric valve. The travel of electric actuator can be divided into 90 ° angle travel and straight travel. Special requirements can also meet the full travel of 180 °, 270 ° and 360 °. The angle travel electric actuator is used together with the angle travel valve to realize the valve 90 ° internal rotation to control the pipeline fluid on and off; The straight stroke electric actuator is used together with the straight stroke valve to realize the up and down movement of the valve plate to control the flow on and off of the pipeline.
2、 Technical principle of electric valve:
The electric valve is usually connected by the electric actuator and the valve, and becomes the electric valve after installation and commissioning. The electric valve uses electric energy as power to connect the electric actuator to drive the valve, so as to realize the opening and closing and regulating actions of the valve. So as to achieve the purpose of switching or regulating the pipeline medium.
Electric valve The drive of is usually driven by a motor. It takes a certain amount of time to complete the opening or closing action, so it can be adjusted. Compare withstand voltage impact. The solenoid valve is quick open and quick close, which is generally used in places with small flow and small pressure, requiring high switching frequency; The electric valve is on the contrary. The opening of the electric valve can be controlled, with the states of open, close, half open and half close. It can control the flow of the medium in the pipeline, but the solenoid valve can not meet this requirement.
The three wire electric valve has three lines F/R/N, F represents the forward action (or open action) control line, R represents the reverse action (or close action) control line, and N represents the ground wire. Solenoid valve is a kind of electric valve; The magnetic field generated by the solenoid coil is used to pull the valve core, so as to change the on-off of the valve body. When the coil is powered off, the valve core will return by the pressure of the spring.
3、 What kinds of electric valves are available:
1. According to the valve position function, the electric valve can be divided into: switching electric valve and regulating electric valve;
2. According to the valve position, it can be divided into: electric ball valve and electric butterfly valve;
3. According to the shape of valve body, it can also be divided into: ordinary electric valve and micro electric valve;
4. The electric valve is usually of on-off type and regulating type;
5. According to the wiring, there are three wire system and two wire system. Large diameter is mostly three wire system, and small diameter can be two wire system and three wire system.
4、 Operating environment of electric valve:
In addition to pipeline parameters, special attention should be paid to the working environment conditions of electric valves, because the electric device in electric valves is an electromechanical device, and its working conditions are greatly affected by its working environment. Generally, the working environment of electric valves is as follows:
1. Indoor installation or outdoor use with protective measures;
2. Outdoor installation, with wind, sand, rain, sun and other erosion;
3. Combustible gas/liquid or dust environment;
4. Environment in humid and dry tropics;
5. The medium temperature of the pipeline is above 480 ℃;
6. The ambient temperature is below - 20 ℃;
7. Vulnerable to flooding or immersion;
8. Environment with radioactive substances (nuclear power plant and radioactive substance test device);
9. Environment on ships or docks (with salt fog, mould and humidity);
10. Occasions with severe vibration;
11. Places prone to fire;
For electric valves in the above environment, the structure, materials and protective measures of electric devices are different. Therefore, the corresponding valve electric device shall be selected according to the above working environment.
5、 Functional requirements of electric valve:
According to the engineering control requirements, the control function of the electric valve is completed by the electric device. The purpose of using electric valve is to realize non manual electrical control or computer control by opening, closing and regulating the valve. At present, the use of electric devices is not only to save manpower. Since the functions and quality of products from different manufacturers vary greatly, the selection of electric devices and valves are equally important to the project.
The valve electric device is an indispensable equipment for realizing valve program control, automatic control and remote control. Its movement process can be controlled by the stroke, torque or axial thrust. Since the working characteristics and utilization rate of the valve electric actuator depend on the type of valve, the working specification of the actuator and the position of the valve on the pipeline or equipment, the correct selection of the valve electric actuator is critical to prevent overload (the working torque is higher than the control torque).
6、 Attention shall be paid to the following points when selecting electric valves:
1. Operating torque The operating torque is the most important parameter for selecting the electric device of the valve. The output torque of the electric device should be 1.2~1.5 times of the maximum operating torque of the valve.
2. There are two main engine structures for operating the thrust valve electric device: one is to output torque directly without a thrust disc; The other is to configure a thrust disc, and the output torque is converted into output thrust through the stem nut in the thrust disc.
3. The number of turns of the output shaft of the valve electric device The number of turns of the output shaft of the valve electric device is related to the nominal diameter of the valve, the screw pitch of the valve stem, and the number of thread heads, which should be calculated as M ＝ H ／ ZS (M is the total number of turns that the electric device should meet, H is the opening height of the valve, S is the screw pitch of the valve stem drive thread, and Z is the number of thread heads of the valve stem).
4. For multi turn rising stem valves, if the maximum valve stem diameter allowed by the electric device cannot pass through the valve stem of the valve, it cannot be assembled into an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric device must be greater than the outer diameter of the stem of the rising stem valve. For some rotary valves and non rising stem valves in multi rotary valves, although the passage of the valve stem diameter is not considered, the valve stem diameter and the size of the keyway should also be fully considered when selecting, so that they can work normally after assembly.
5. If the opening and closing speed of the output speed valve is too fast, water hammer is likely to occur. Therefore, proper opening and closing speed shall be selected according to different service conditions.
6. The electric device of the valve has its special requirements, that is, it must be able to limit the torque or axial force. Usually, the valve electric device adopts the coupling that limits the torque. When the specification of the electric device is determined, its control torque is also determined.
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