Valve electric actuators have special requirements, that is, they must be able to limit torque or axial force. Usually, valve electric actuators use torque limiting couplings. After the specification of the electric actuator is determined, its control torque is also determined. Generally, it runs within a predetermined time and the motor will not overload. But if the following situations occur, it may lead to overload: firstly, the power supply voltage is low and the required torque cannot be obtained, causing the motor to stop rotating; The second is to mistakenly set the torque limiting mechanism to exceed the stopping torque, causing continuous excessive torque generation and causing the motor to stop rotating; The third is intermittent use, which generates heat accumulation that exceeds the allowable temperature rise of the motor; Fourthly, due to some reason, the circuit of the torque limiting mechanism malfunctions, resulting in excessive torque; The fifth reason is that the operating environment temperature is too high, which relatively reduces the thermal capacity of the motor.

The distribution of the valve market is mainly based on the construction of engineering projects. The major users of valves are the petrochemical industry, power sector, metallurgical sector, chemical industry, and urban construction sector. The petrochemical industry mainly applies API standard gate valves, globe valves, and check valves; The power department mainly uses high-temperature pressure gate valves, globe valves, check valves, and valves for power stations, as well as low-pressure butterfly valves and gate valves for some water supply and drainage valves; The chemical industry mainly uses stainless steel gate valves, globe valves, and check valves; The metallurgical industry mainly uses low-pressure large-diameter butterfly valves, oxygen globe valves, and oxygen ball valves; The urban construction department mainly uses low-pressure valves, such as large-diameter gate valves for urban water pipelines, midline butterfly valves for residential construction, and metal sealed butterfly valves for urban heating; Oil pipelines mainly use flat gate valves and ball valves; The pharmaceutical industry mainly uses stainless steel ball valves; The food industry mainly uses stainless steel ball valves, etc.　　

Valve electric actuators are indispensable equipment for achieving valve programming, automatic control, and remote control, and their movement process can be controlled by the magnitude of stroke, torque, or axial thrust. Due to the fact that the working characteristics and utilization of valve electric actuators depend on the type of valve, the operating specifications of the device, and the position of the valve on the pipeline or equipment, the correct selection of valve electric actuators is crucial to prevent overloading (working torque higher than control torque).

Usually, the correct basis for selecting valve electric actuators is as follows:

The operating torque is the main parameter for selecting valve electric actuators, and the output torque of the electric actuator should be 1.2~1.5 times the larger operating torque of the valve.

There are two main structures for operating thrust valve electric actuators: one is to output torque directly without a thrust disc; Another option is to configure a thrust disc, where the output torque is converted into output thrust through the valve stem nut in the thrust disc.

The number of output shaft rotations of a valve electric actuator is related to the nominal diameter, valve stem pitch, and number of thread heads of the valve. It should be calculated according to M=H/ZS (M is the total number of rotations that the electric device should meet, H is the valve opening height, S is the valve stem transmission thread pitch, and Z is the number of valve stem thread heads). For multi turn rising stem valves with stem diameter, if the larger stem diameter allowed by the electric actuator cannot pass through the valve stem of the equipped valve, it cannot be assembled into an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric actuator must be greater than the outer diameter of the stem of the rising stem valve. For non rising stem valves in partial rotation valves and multi rotation valves, although the diameter of the valve stem does not need to be considered, the size of the valve stem diameter and keyway should also be fully considered during selection to ensure normal operation after assembly.

If the opening and closing speed of the output speed valve is too fast, it is easy to cause water hammer phenomenon. Therefore, the appropriate opening and closing speed should be selected based on different usage conditions

In the past, the methods of protecting motors were to use fuses, overcurrent relays, thermal relays, thermostats, etc., but each of these methods had its own advantages and disadvantages. There is definitely no reliable protection method for variable load equipment such as electric actuators. Therefore, various combination methods must be adopted, which can be summarized into two types: one is to judge the increase or decrease of the motor input current; The second is to judge the heating condition of the motor itself. Both of these methods need to consider the time margin given by the motor's thermal capacity.

Usually, the basic protection method for overload is to use a thermostat for overload protection during continuous operation or jog operation of the motor; Thermal relays are used to protect the motor from stalling; For short circuit accidents, use fuses or overcurrent relays.