The correct selection of electric actuator for electric gate valve is based on the following points:
1. operating torque: the operating torque is the most important parameter for selecting the electric device of the gate valve. The output torque of the electric actuator shall be 1.2 ~ 1.5 times of the maximum operating torque of the gate valve.
2. there are two main machine structures for operating the electric device of thrust gate valve: one is to directly output torque without thrust disc; The other is equipped with a thrust disc, and the output torque is converted into output thrust through the valve rod nut in the thrust disc.
3. number of output shaft turns: the number of output shaft turns of the electric device is related to the nominal diameter of the gate valve, the screw pitch of the valve stem and the number of screw heads, and shall be calculated according to m ＝ h ／ ZS (M is the total number of turns that the electric device should meet, h is the opening height of the gate valve, s is the screw pitch of the valve stem transmission thread, and Z is the number of screw heads of the valve stem).
4. for the multi turn rising stem gate valve, if the maximum stem diameter allowed by the electric device cannot pass through the stem of the equipped gate valve, it cannot be assembled into an electric gate 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 rising stem gate valve. For some rotary gate valves and Non rising stem gate valves in multi rotary gate valves, although the passage of the valve stem diameter is not considered, the valve stem diameter and the size of the keyway shall also be fully considered in the selection, so that they can work normally after assembly.
5. output speed: if the opening and closing speed of the gate valve is too fast, it is easy to produce water hammer. Therefore, the proper opening and closing speed shall be selected according to different service conditions.
6. the electric actuator of gate valve has special requirements, that is, it must be able to limit torque or axial force. Usually, the electric device of the gate valve adopts the coupling to limit the torque. When the specification of the electric device is determined, its control torque is also determined.
Generally, it operates within a predetermined time, and the motor will not be overloaded. However, overload may occur if:
1、 Because the power supply voltage is low, the required torque cannot be obtained, so that the motor stops rotating;
2、 It is wrong to set the torque limiting mechanism to make it greater than the stopping torque, resulting in continuous excessive torque and stopping the motor;
3、 It is used intermittently, and the heat accumulated exceeds the allowable temperature rise of the motor;
4、 It is the fault of the torque limiting mechanism circuit for some reason, which makes the torque too large;
5、 It is that the operating ambient temperature is too high, which relatively reduces the thermal capacity of the motor.
6、 The basic protection method for overload is:
1. for overload protection of continuous operation or inching operation of motor, thermostat shall be used;
2. thermal relay shall be used for motor locked rotor protection;
3. for short circuit accident, fuse or overcurrent relay shall be used
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