In pipeline engineering, the correct selection of electric valves is one of the guarantee conditions to meet the requirements of use. If the electric valve used is not properly selected, it will not only affect the use, but may also cause serious losses. So, how do we use electric valves correctly?
The electric valve is to use an electric actuator to control the valve, so as to realize the opening and closing of the electric valve. It can be divided into upper and lower parts, the upper part is the electric actuator, and the lower part is the valve. It can also be called an air-conditioning valve.
The electric valve is a high-end product in the automatic control valve. It can not only realize the switching function, but the regulating electric valve can also realize the valve position adjustment function. The stroke of the electric actuator can be divided into three types: 90° angular stroke (VITAL-R series, VITAL-Q series), linear stroke (VITAL-QL series, VITAL-L series) and multi-turn (VITAL-M series). Special requirements can also meet the full stroke of 180°, 270°, and 360°. The quarter-stroke electric actuator is used in conjunction with the quarter-stroke valve to realize the internal rotation of the valve within 90° to control the on-off of the pipeline fluid; the straight-stroke electric actuator is used with the straight-stroke valve to realize the up and down movement of the valve plate to control the on and off of the pipeline fluid.
2. Technical Principle
Electric valves are usually connected by electric actuators and valves, and become electric valves after installation and debugging. Electric valves use electric energy as power to turn on the electric actuator to drive the valve to realize the on-off and regulating actions of the valve. So as to achieve the purpose of switching or adjusting the pipeline medium.
The driving of the electric valve is generally by a motor, and it takes a certain amount of time to complete the opening or closing action, which can be adjusted. Solenoid valves are fast-opening and fast-closing. They are generally used in places where small flow and low pressure require high switching frequency; electric valves are the opposite. The opening degree of the electric valve can be controlled, and the state is open, closed, half-open and half-closed, which can control the flow of the medium in the pipeline, but the solenoid valve cannot 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 line. Solenoid valve is a type of electric valve; it uses the magnetic field generated by the solenoid coil to pull the valve core, thereby changing the on and off of the valve body, the coil is de-energized, and the valve core retreats by the pressure of the spring.
3. What types of electric valves are there?
1. According to the function of valve position, the electric valve can be divided into: on-off 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 the valve body, it can also be divided into: ordinary electric valve and miniature electric valve;
4. Electric valves are usually on-off type and regulating type;
5. According to the wiring, there are three-wire and two-wire systems. The large-diameter ones are mostly three-wire systems, and the small-diameter ones have two-wire and three-wire systems.
In addition to paying attention to pipeline parameters, electric valves should also pay special attention to their working environmental conditions, because the electric device in electric valves is an electromechanical device, and its working conditions are greatly affected by its working environment. Under normal circumstances, the working environment of the electric valve is as follows:
1. Indoor installation or outdoor use with protective measures;
2. Outdoor installation is exposed to erosion by wind, sand, rain, dew, and sunlight;
3. It has a flammable and explosive gas or dust environment;
4. Environment in humid and dry tropics;
5. The temperature of the pipeline medium is above 480℃;
6. The ambient temperature is lower than -20℃;
7. Easy to be flooded or immersed in water;
8. Environment with radioactive material (nuclear power plant and radioactive material testing device);
9. The environment on the ship or dock (with salt spray, mold, humidity);
10. Occasions with severe vibration;
11. Occasions prone to fire;
For the electric valve in the above environment, the structure, material and protective measures of the electric device are different. Therefore, the corresponding VITAL electric actuator should be selected according to the above working environment.
4. Functional requirements for electric valves
According to engineering control requirements, for electric valves, its control function is completed by electric devices. The purpose of using electric valves is to realize non-manual electrical control or computer control of valve opening, closing and adjustment linkage. The current use of electric devices is not just to save manpower. Because the functions and quality of products from different manufacturers are quite different, the selection of AOX electric actuators and the selection of the valves are equally important to the project.
VITAL electric actuator is an indispensable device to realize valve program control, automatic control and remote control. Its movement process can be controlled by stroke, torque or axial thrust. Since the working characteristics and utilization of the valve electric device depend on the type of valve, the working specifications of the device and the position of the valve on the pipeline or equipment, the correct selection of VITAL electric actuators can prevent overloading (the working torque is higher than Control torque) is very important.
5. Attention should be paid to the following points when selecting electric valves:
1. Operating torque is the main parameter for selecting electric valve electric actuators. The output torque of the electric actuator should be 1.2 to 1.5 times the valve operating torque.
2. There are two main structures for operating thrust valve electric actuators: one is not equipped with a thrust plate, and the torque is directly output; the other is with a thrust plate, and the output torque is converted into output thrust through the valve stem nut in the thrust plate.
3. Number of turns of the output shaft The number of turns of the output shaft of the valve electric actuator is related to the nominal diameter of the valve, the pitch of the valve stem, and the number of thread heads. It should be calculated according to M=H/ZS (M is what the electric device should meet The total number of turns, H is the opening height of the valve, S is the thread pitch of the valve stem, and Z is the number of stem threads).
4. Valve stem diameter For multi-turn rising stem valves, if the diameter of the stem allowed by the electric actuator cannot pass through the stem of the matched valve, it cannot be assembled into an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric actuator must be larger than the outer diameter of the stem of the rising stem valve. For part-turn valves and dark-stem valves in multi-turn valves, although the passage of the stem diameter does not need to be considered, the stem diameter and the size of the keyway should be fully considered when selecting and matching, so that it can work normally after assembly.
5. If the opening and closing speed of the output speed valve is too fast, water hammer will easily occur. Therefore, the appropriate opening and closing speed should be selected according to different conditions of use.
6. Electric valve actuators have special requirements, that is, they must be able to limit torque or axial force. Usually the valve electric device adopts a torque-limiting coupling. When the specifications of the electric device are determined, its control torque is also determined.