1. Correct Selection of Valve Electric Actuators
Basis for Selection:
Operating Torque: Operating torque is the main parameter for selecting a valve electric actuator.The output torque of the electric actuator should be 1.2 to 1.5 times the valveoperating torque。

 There are two main structures for push-type valve electric actuators: one without a thrust plate, directly outputting torque; the other with a thrust plate, converting output torque into output thrust through the valve stem nut on the thrust plate.

Number of Turns of Output Shaft: The number of turns of the valve electric actuator output shaft is related to the valve nominal diameter, valve stem pitch, and number of thread starts. It should be calculated as M = H/ZS (where M is the total number of turns the actuator should meet, H is the valve opening height, S is the valve stem thread pitch, and Z is the number of valve stem threads).

Valve Stem Diameter: For multi-turn rising stem valves, if the maximum valve stem diameter allowed by the actuator cannot pass through the valve stem of the valve, it cannot be assembled into an electric valve. Therefore, the inner diameter of the hollow output shaft of the actuator must be larger than the outer diameter of the valve stem. For some rotary valves and non-rising stem valves in multi-turn valves, although the stem diameter clearance may not need to be considered, the stem diameter and keyway size should be fully considered during selection to ensure normal operation after assembly.

Output Speed: If the valve opens and closes too quickly, it can cause water hammer. Therefore, an appropriate opening and closing speed should be selected according to different working conditions.

Electrical valve actuators have special requirements, meaning they must be able to limit torque or axial force. Usually, torque-limiting couplings are used. Once the actuator specification is determined, the control torque is also set. Typically, when running within a specified time, the motor will not overload.

2. However, the following situations may cause overload:

Low power supply voltage, resulting in insufficient torque to operate the motor;

Incorrect setting of the torque-limiting mechanism, causing torque to exceed the stop torque, which may repeatedly generate excessive torque and stop the motor;

Intermittent use, causing cumulative heat exceeding the motor's allowable temperature rise;
Failure of the torque-limiting mechanism due to some circuit malfunction, resulting in excessive torque;

High ambient temperature, effectively reducing motor capacity.

In the past, fuses, overcurrent relays, relays, and thermostats were used to protect motors, each with pros and cons. Variably loaded devices like electrical equipment have no reliable protection method. Therefore, various combination methods must be used, generally summarized into two approaches: monitoring the increase or decrease of motor input current, or monitoring the motor itself. Regardless of the method, the motor's given time margin must be considered.

3. Basic Methods for Overload Protection

For continuous or jog operation overload protection, use a thermostat;
To protect the motor from stalling, use a relay;
For short circuits or accidental occurrences, use fuses or overcurrent relays.