Valve actuators valve is programmed to achieve self-control and remote control essential equipment, the movement by stroke, torque or to control the size of the axial thrust. Because the operating characteristics of electric valve actuators and utilization depends on the type of valves, fittings and valves in the pipeline work norms or the location of the device, so the correct choice of electric valve device to prevent overload of the phenomenon (work transfer moments higher than the control torque) is essential. Torque operation is to select the valve operating torque of the main parameters of electric devices, electric equipment output valve operating torque should be the maximum torque of 1.2 to 1.5 times. Thrust electric valve actuators operating the host structure, there are two: one is not configured thrust plate, the direct output torque; the other is the thrust plate configuration, the output torque of the valve stem nut through the thrust plate is converted to output thrust. Output shaft revolutions electric valve actuators output shaft revolutions and the number of the valve nominal diameter, stem pitch, the first few threads, according to M = H / ZS calculated (M is the total electric device should meet the rotation number, H is the valve opening height, S is the stem transmission thread pitch, Z for the first few stem thread). Stem diameter class for the next shot multi-turn valves, electrical equipment if the maximum allowed by the stem diameter can not pass the valve stem with, it can not be assembled into electric valve. Therefore, the electric device inside diameter of the hollow output shaft must be greater than the next shot of the valve stem diameter. On the part of the rotary valve and rotary valve valve rod in the dark, although not considered by the stem diameter, but should also take full account of the matching stem diameter and keyway sizes, so that after assembly to work . Output speed of the valve opening and closing speed if fast, easy to produce water hammer phenomenon. Therefore, according to the different conditions of use, choose the appropriate opening and closing speed. Electric valve actuators have special requirements that must be able to limit the torque or axial force. Usually limit the use of electric valve actuators torque coupling. When the electric device specifications determined, the control torque is also determined. Generally operate within a predetermined time, the motor will not overload. However, if the following conditions may lead to overload: First, the supply voltage is low, not the required torque, the motor stops rotating; the second is wrong it is set torque limit institutions to stop the torque is greater than , resulting in continuous excessive torque, the motor stops rotating; Third, intermittent use, savings generated by the heat, more than the allowable temperature rise of the motor; Fourth, institutions for some reason the torque limit circuit fault, the torque is too large; Fifth, the ambient temperature is too high, the relative decline in the motor thermal capacity.