This paper introduces the selection of electric actuator in detail. If you think the answer is helpful to you, please give a compliment to the American Witton VTON valve.
Imported electric valves mainly include imported electric butterfly valves, imported electric ball valves and imported electric regulating valves.
The electric actuator of imported valve refers to the machinery that uses electric energy as the main energy to drive the valve. Because it is a precision electrical component, it is generally required to have a certain explosion-proof and protection level (waterproof and dustproof);
According to the applicable working conditions, it can be divided into explosion-proof type and ordinary type; According to the voltage, it is mainly divided into AC380V, AC220V and DC 24 V; According to the action mode of the actuator, it can be divided into switch type and adjustment type.
Referring to the classification of American Wheaton VTON electric actuators, actuators can be divided into? Multi-spin, angular stroke and straight stroke. According to the upper computer signal control mode can be divided into? Switch type, regulating type and field bus type;
Imported electric actuator
Valve electric actuator is an indispensable equipment to realize valve program control, automatic control and remote control, and its movement process can be controlled by stroke, torque or axial thrust. Because the working characteristics and utilization rate of 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. Therefore, the correct selection of valve electric device is very important to prevent overload (working torque is higher than control torque).
Generally speaking, the reference basis for the correct selection of imported valve electric devices is as follows (taking the selection of VTON electric actuator in Wilton, USA as an example):
1 operating torque
Operating torque, also called valve torque, is the most important parameter for selecting valve electric device, and the output torque of electric device should be 1.2~ 1.5 times of the maximum operating torque of the valve.
2 working thrust
There are two main engine structures of valve electric device: one is to directly output torque without thrust plate; The other is to configure a thrust disc, and the output torque is converted into output thrust through the valve stem nut in the thrust disc.
3 Number of revolutions of output shaft
The number of revolutions of the output shaft of the valve electric device is related to the nominal diameter of the valve, the pitch of the valve stem and the number of thread heads, and should be calculated as M=H/ZS (m is the total number of revolutions that the electric device should meet, h is the opening height of the valve, s is the pitch of the valve stem transmission, and z is the number of thread heads of the valve stem).
4 protection level
Electric actuators have protection level, that is, IP requirements. The related concepts of protection level are introduced here. IP (entrance protection) protection level system was drafted by IEC (International Electrotechnical Commission). Lamps are classified according to their dustproof and moistureproof characteristics. The foreign objects mentioned here, including tools and people's fingers, must not touch the live parts in the lamps to avoid electric shock. The IP protection level consists of two numbers, 1 number indicates the level of keeping lamps away from dust and preventing foreign bodies from invading, and the second number indicates the tightness of lamps against moisture and water invasion. The higher the number, the higher the protection level.
For example, the protection grades of electric actuators selected for imported electric butterfly valves, imported electric ball valves and imported electric regulating valves of Weidun VTON in the United States are generally IP65, IP66 and IP67.
5. Explosion-proof grade of electric actuator
The commonly used explosion-proof grades of explosion-proof electric actuators are ExdIIBT4 and ExdIIBT6, which are often used in the field. Yangzhou Bell briefly introduces the main difference between these two explosion-proof grades: T4 and T6 represent the surface temperature of explosion-proof electrical equipment, which is the temperature at which any component of electrical equipment may cause fire in the surrounding explosion environment when the electrical equipment works under unfavorable operating conditions within the specified range. The temperature should be lower than the flammable temperature:
For example, if the ignition temperature of explosive gas in the sensor environment is 100℃, the surface temperature of any component of the sensor should be lower than 100℃ under harsh working conditions. The surface temperature group of electrical equipment is T 1-T6:
T 1:450 degrees Celsius, T2:300 degrees Celsius, T3 200 degrees Celsius, T4? 135℃, T5 100℃, T6 85℃.
For example, American Weidun VTON imported electric butterfly valve, imported electric ball valve and imported electric regulating valve. The explosion-proof grade of electric actuator is ex Ⅱ bt4? BT6, etc.
6, stem diameter
For multi-turn open stem valves, if the maximum diameter of the valve stem allowed by the electric device cannot pass through the valve stem, it cannot be assembled into an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric device must be larger than the outer diameter of the stem of the exposed stem valve. For some rotary valves and hidden stem valves in multi-rotary valves, it is not necessary to pass the valve stem diameter, but the valve stem diameter and keyway size should be fully considered in the selection to make them work normally after assembly.
7 output speed
If the opening and closing speed of the valve is too fast, it is easy to produce water hammer. Therefore, the appropriate opening and closing speed should be selected according to different use conditions.
Valve electric device has its special requirements, that is, it must be able to limit torque or axial force. Usually, the valve electric device uses a coupling that limits torque. When the specification of the electric device is determined, its control torque is also determined. Generally, it runs within a predetermined time, and the motor will not be overloaded. However, if the following situations occur, it may lead to overload: first, the power supply voltage is low, and the required torque cannot be obtained, so that the motor stops rotating; Secondly, the torque limiting mechanism is wrongly set to be greater than the stopping torque, which leads to the continuous excessive torque and stops the motor; Third, intermittent use leads to heat accumulation, which exceeds the allowable temperature appreciation of the motor; Fourth, the torque limiting mechanism circuit fails for some reason, which makes the torque too large; Fifth, the operating environment temperature is too high, which makes the heat capacity of the motor relatively lower.
In the past, the methods to protect the motor were fuses, overcurrent relays, thermal relays, thermostats and so on. But these methods have their own advantages and disadvantages. There is no absolutely reliable protection method for variable load equipment such as electrical equipment. Therefore, various combinations must be adopted, which can be summarized into two types: one is to judge the increase or decrease of motor input current; The second is to judge the heating condition of the motor itself. These two methods, no matter which one, should consider the time margin given by the heat capacity of the motor.
Usually, the basic protection methods of overload are: in order to protect the motor from discontinuous operation or inching operation, a thermostat is used; The thermal relay is used to prevent the motor from locking and rotating; For short circuit accidents, use fuses or overcurrent relays.