The correct choice of electric device should be based on 1. Operating torque: Operating torque is the most important parameter for selecting the valve electric device.

The output torque of the electric device shall be 1.2~1.5 times of the maximum torque of the valve operation. 2.

Operation Thrust: The main structure of the valve electric device has two kinds, one is not to configure the thrust disk, at this time the direct output torque; the other is configured with a thrust disk, at which point the output torque through the thrust of the stem nut to output thrust. 3. Output shaft rotation number: valve electric device output shaft number of rotation and the valve nominal diameter, stem pitch, the number of threaded head, according to M=h/zs calculation (type: M for the electric device should meet the total number of rotation, H for the valve opening height, mm;s for the valve STEM transmission thread pitch, mm;z for the stem thread head number.

） 4. Stem diameter: For many rotary type of the valve, if the electric device allows the maximum valve stem diameter can not be equipped with valve stem, it can not be assembled into electric valves. Therefore, the inner diameter of the hollow output shaft of the electric device must be greater than the stem diameter of the valve.

For the part of the rotary valve and the valve in many rotary valves, although not to take into account the passage of stem diameter, but in the selection should be fully considered the diameter of the stem and the size of the keyway, so that after the assembly can work properly. 5. Output speed: Valve opening and closing speed, easy to produce water hammer phenomenon.

Therefore, the appropriate opening and closing speed should be chosen according to different conditions of use. 6. installation, connection mode: The installation of electric device has vertical installation, horizontal installation, landing installation, the connection mode is: thrust plate, valve stem through (bright rod multiple slewing valve), dark rod multiple slewing, no thrust plate, valve stem does not pass, the use of partial rotary electric device is very wide, is to realize valve program control, self-control and remote control indispensable equipment, It is mainly used in closed-circuit valves. However, the special requirements of the valve actuator must be limited to the torque or axial force.

Usually the valve electric device adopts a torque-limiting coupling. When the specification of the electric device is determined, the control torque is determined. When it runs in a predetermined time, the motor generally does not overload.

However, it may be overloaded if: 1.

The power supply voltage is low, can not get the required torque, so that the motor stop rotation. 2.

The torque limiting mechanism is incorrectly adjusted to make it larger than the stop torque, which causes a large torque to be produced and the motor stops turning. 3.

such as the intermittent use of moving, the resulting heat savings up, exceeding the allowable temperature of the motor appreciation. 4.

For some reason torque limiting mechanism circuit failure, so that the torque is too large. 5.

The use of ambient temperature is too high, relatively to reduce the thermal capacity of the motor.

These are some of the causes of overload, for these reasons the motor overheating phenomenon should be taken into account, and take measures to prevent overheating. In the past, the protection of the motor is the use of fuses, overcurrent relays, thermal relays, thermostat, etc., but these methods have their pros and cons, for electric devices such variable load equipment, absolutely reliable protection is not. It is therefore necessary to adopt various methods of combination. However, because of the different load of each electric device, it is difficult to propose a unified approach.

But in general, you can find common ground.

The overload protection method is taken into two kinds 1.

To judge the increase or decrease of the input current of the motor; 2.

To judge the heat of the motor itself. Both of the above methods, regardless of the type of motor heat capacity to consider the given time allowance. It is difficult to align it with the thermal capacity of the motor in a single way.

Therefore, we should choose a method based on overload, which can be used for reliable action-combination method, in order to achieve comprehensive overload protection. The motor of the Rotork electric device, because it is embedded in the winding with the motor insulation grade consistent thermostat, when the rated temperature, the motor control circuit will be cut off.

The thermal capacity of the thermostat itself is small, and its time-limited characteristics are determined by the thermal capacity characteristics of the motor, so this is a reliable method.

The basic protection method of overload 1.

The thermostat is used for the overload protection of the motor running continuously or the operation of the point movement; 2.

The protection of motor plugging is adopted by thermal relay; 3.

A fuse or overcurrent relay is used for short circuit accidents. The correct selection of the valve electric device and the overload prevention are related and should be paid attention to.