Metallurgy, energy and minerals correctly select the valve electric device to prevent overload. The valve electric device is one of the devices used to operate the valve and connect it to the valve. The device is driven by electricity, and its movement process can be controlled by stroke, torque or axial thrust. Because the working characteristics and utilization rate of the valve electric device should depend on the type of valve, the working specification of the device and the position of the valve on the pipeline or equipment. Therefore, to grasp the correct choice of valve electric device; to consider the prevention of overload (working torque is higher than the control torque) has become a crucial part. The correct choice of electric valve device should be based on: 1. Operating torque: The operating torque is the most important parameter for selecting the valve electric device. The output torque of the electric device should be 1.2 to 1.5 times the maximum torque of the valve operation. 2. Thrust operation: There are two types of main structure of the valve electric device, one is not equipped with a thrust disc, and the torque is output directly; the other is configured with a thrust disc, and the output torque is passed through the valve in the thrust disc The rod nut is converted to output thrust. 3. The number of rotations of the output shaft: the number of rotations of the output shaft of the valve electric device is related to the nominal diameter of the valve, the thread pitch of the valve stem, and the number of thread heads. The total number of rotations satisfied; H is the opening height of the valve, mm; S is the pitch of the stem drive thread, mm; Z is the number of stem threads 4. Stem diameter: For open stem valves of multi-turn type, if the maximum stem diameter allowed by the electric device cannot pass through the 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 open stem valve. For part-turn valves and concealed-rod valves in multi-turn valves, although there is no need to consider the passage of the stem diameter, the stem diameter and keyway size should also be fully considered during the selection to enable normal operation after assembly. 5. Output speed: The valve opens and closes quickly, which is prone to water hammer. Therefore, appropriate opening and closing speeds should be selected according to different operating conditions. 6. Installation and connection methods: The installation methods of the electric device are vertical installation, horizontal installation, and floor installation; the connection methods are: with the thrust disc valve stem passing (open rod multi-turn valve), the dark rod multi-turn without thrust disc stem does not pass Part-turn electric devices are widely used, and are indispensable equipment for realizing valve program control, automatic control and remote control. They are mainly used in closed-circuit valves. But the special requirements of the valve electric device cannot be ignored-it must be able to limit the torque or axial force. Valve electric devices usually use couplings that limit torque. After the specifications of the electric device are determined, its control torque is also determined. When it runs within a predetermined time, the motor is generally not overloaded. However, it can be overloaded if the following conditions occur: 1. The power supply voltage is low, the required torque cannot be obtained, and the motor stops rotating. 2. The torque limiting mechanism is erroneously set so that it is greater than the stopping torque, causing excessive torque to be continuously generated and stopping the motor. 3. When used intermittently as a jog, the heat generated is accumulated and exceeds the allowable temperature rise of the motor. 4. For some reason, the circuit of the torque limiting mechanism fails, which makes the torque too large. 5. If the ambient temperature is too high, the thermal capacity of the motor will be relatively reduced. The above are some reasons for overloading. The motor overheating caused by these reasons should be considered in advance and measures should be taken to prevent overheating. In the past, the way to protect the motor was to use fuses, overcurrent relays, thermal relays, thermostats, etc., but these methods also have their own advantages and disadvantages. For electric equipment such as load-changing equipment, there is no absolutely reliable protection . Therefore, a combination of various methods must be adopted. However, due to the different load conditions of each electric device, it is difficult to propose a unified method. But in most cases, you can also find common ground. The overload protection methods adopted can be summarized into two types: 1. Judge the increase or decrease of the motor input current; 2. Judge the motor itself to generate heat. The above two methods, regardless of the type, must consider the time margin given by the motor thermal capacity. It is difficult to make it consistent with the thermal capacity characteristics of the motor in a single way. Therefore, we should choose a method that can act reliably according to the cause of overload-a combined compound method to achieve comprehensive overload protection. The motor of the Rotork electric device is buried in the winding with a thermostat consistent with the insulation level of the motor. When the rated temperature is reached, the motor control circuit will be cut off. The thermal capacity of the thermostat is relatively small, and its time-limiting characteristics are determined by the thermal capacity characteristics of the motor, so this is a reliable method. The basic protection method of overload is: 1. Use thermostat for overload protection of motor continuous operation or jog operation; 2. Use thermal relay for protection of motor stall 3. Use fuse or overcurrent relay for short circuit accident. The correct choice of valve electric device and the prevention of overload are closely related. Should be valued
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