Valve actuators are one of the devices used to operate the valve and connect it to the valve. The device is powered by electricity and its movement can be controlled by stroke, torque or axial thrust. The proper operating characteristics and utilization of valve actuators depend on the type of valve, the work specifications of the device and the position of the valve on the pipeline or equipment.
Choose by:
1. Operating thrust. There are two kinds of the main structure of the valve electric device, one is not configured thrust plate; the other is equipped with a thrust plate.
2. Operating torque. Operating torque is the choice of the most important parameters of the valve electric device.
3. Stem diameter. Motorized valves can not be assembled if the maximum stem diameter allowed by the actuator does not pass through the stem of the fitted valve.
Valve actuators are usually torque-limiting couplings. When the specifications of the electric device is confirmed, the control torque is also determined. When it is operating within a predetermined time, the motor is generally not overloaded.
However, it can be overloaded if:
1. The power supply voltage is low, the required torque can not be obtained, so that the motor stops rotating.
2. Wrongly set the torque limiting mechanism, it is greater than the stop torque, resulting in continuous generation of excessive torque, the motor stops rotating.
3. As intermittent use of jogging, the heat generated savings, exceeding the allowable temperature rise of the motor value.
4. For some reason, the circuit of the torque limit mechanism is faulty, so that the torque is too large.
5. The use of ambient temperature is too high, relative to the motor heat capacity decreased.
Therefore, we must adopt a combination of methods. However, due to the different loading conditions of each electric device, it is difficult to propose a unified approach. But in most cases, you can also find common ground.
Take the overload protection, summarized in two ways:
1. To determine the increase or decrease of the motor input current;
2. Judge the motor itself fever. The above two methods, regardless of the kind to consider the motor thermal capacity given time margin. If a single way to make it consistent with the thermal characteristics of the motor is difficult. Therefore, we should choose a reliable method of action based on the cause of overload - a combination of complex ways to achieve a comprehensive overload protection.
The basic method of overload protection is:
1. The thermostat is used for overload protection of the motor in continuous operation or inching operation;
2. The protection of motor stalls using thermal relays
3. For short-circuit accident fuse or over-current relay. The correct choice of valve electric devices and overload prevention is related, should be taken seriously.
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