Proper selection of motorized valve actuators should be noted.

Valve electric device is one of the devices used to operate the valve and connect the valve. The device is driven by electricity, and its motion can be controlled by the size of travel, torque or axial thrust. The operating characteristics and utilization of valve actuators depend on the type of valve, the working specification of the device and the position of the valve on the line or equipment. Therefore grasp the correct choice of valve electric device; It is important to consider preventing overloading (the working torque is higher than the control torque).
Correct selection of valve electric device shall be based on:

1. Operating torque: the operating torque is the main parameter to select the valve electric device. The output torque of the electric device shall be 1.2 ~ 1.5 times the maximum torque of the valve operation.

2. Operation thrust: the main structure of the valve electric device is two kinds, one is not to configure the thrust plate, and the direct output torque; The other is the configuration of the thrust plate, when the output torque is converted from the stem nut in the thrust plate to the output thrust.

3. Output shaft rotation circle count: the number of laps valve electric actuator output shaft rotation with nominal diameter of the valve, the valve stem thread pitch, thread, calculated at M = H/ZS (type: M for electric devices should satisfy the total number of rotating ring; H for valve opening height, mm; S is the screw pitch of stem transmission thread, mm; Z is the number of stem threads.

4. Stem diameter: if the maximum stem diameter of an electric device is not allowed to pass through the valve stem, the valve is not assembled into an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric device must be greater than that of the stem valve. For part of the rotary valve and multi-turn valves of non-rising stem valves, although need not consider stem diameter through the problem, but also should fully consider when selecting the valve stem diameter and the size of the keyway, after assembly to work properly.

5. Output speed: quick opening and closing speed of valve, easy to produce water hammer. Therefore, according to different conditions of use, choose the appropriate opening and closing speed.

6. Installation and connection mode: the installation mode of the electric device has vertical installation, horizontal installation and installation; The connection mode is: thrust disc; The stem is passed through (the open rod multi-turn valve); The dark rod is more rotary; No thrust plate; The stem does not pass; Part of the rotary electric device is widely used, which is an indispensable equipment for valve control, automatic control and remote control. It is mainly used in closed circuit valves. But the special requirement of valve electric device cannot be ignored - it must be able to limit torque or axial force. Normally the valve electric device USES a shaft that limits torque.

When the specification of the electric device is determined, the control torque is also determined. When it is run in a predetermined time, the motor does not normally overload. However, if the following situations occur, they may be overloaded:

1. The power supply is low and the torque is not needed, so that the motor stops rotating.

2. The torque limitation mechanism is adjusted by mistake, which is greater than the stop torque, which causes the continuous excessive torque to stop the motor turning.

3. If the action is broken, the amount of heat accumulated will exceed the allowable temperature of the motor.

4. For some reason torque limit mechanism circuit failure, make torque too large.

5. The use of ambient temperature is too high, and the thermal capacity of the motor is reduced.

These are some of the reasons for the overload. The overheating of the motor caused by these reasons should be taken into account in advance and measures should be taken to prevent overheating.

Past the motor protection method is to use a fuse, overcurrent relay, thermal relay, thermostat, etc., but these measures also are each have advantages and disadvantages, for this kind of variable load equipment, electric actuator is not absolutely reliable measures for the protection of. So there must be a combination of methods. However, due to the different load conditions of each electric device, it is difficult to propose a unified approach. But generalizations can also be found in common.

There are two kinds of overload protection methods:

1. To judge the increase and decrease of motor input current;

2. Judge the heating of the motor itself.

In both cases, the amount of time that the motor heat capacity is given should be considered. It is difficult to match the thermal capacity of the motor in a single way. Therefore, it is necessary to choose the method that can be reliable according to the reason of overload - composite method, to achieve comprehensive overload protection.

The motor of the rotok electric device, because it is embedded in the windings of the thermostat that is consistent with the insulation grade of the motor, when it reaches the rated temperature, the motor control circuit will be cut off. The thermostat itself has a small thermal capacity and is determined by the thermal capacity of the motor, so this is a reliable method.

The basic protection method of overload is:

1. The thermostat is used to protect the overload protection of the motor running or the point operation.

2. Thermal relay is adopted for the protection of motor plugging.

3. Fuse or overcurrent relay for short circuit accident.

The correct choice of valve electric equipment and the prevention of overload are closely related and should be taken seriously.