How the valve electric actuator prevents overload?
Valve electric Actuator is an indispensable equipment to realize valve programmable, automatic control and remote control, and its motion process can be controlled by the size of stroke, torque or axial thrust.
Since the working characteristics and utilization rate of the valve electric actuator depend on the type of valve, the operating specification of the device and the position of the valve on the pipeline or equipment, it is very important to select the valve electric actuator correctly to prevent overload (the working torque is higher than the control torque).
In general, the correct selection of valve electric actuators is based on the following:
The operating torque operation torque is the most important parameter to select the valve electric actuator, and the output torque of the electric device should be 1.2~1.5 times the maximum torque of the valve operation.
Operation Thrust Valve The main structure of the electric actuator has two kinds: one is not to configure the thrust disk, direct output torque, the other is to configure the thrust disk, the output torque through the thrust disk of the stem nut converted to the output thrust.
Output shaft rotation ring number valve electric actuator output shaft number of rotating ring is related to the valve nominal diameter, stem pitch, number of threaded head, to be calculated according to M=h/zs (m for the electric device should meet the total number of rotating ring, H for the valve opening height, s for the stem drive thread pitch, Z is the number of stem threaded head). The stem diameter of the multi-rotary type Rod valve, if the electric device allows the maximum stem diameter can not pass through the valve rod of the valve, it can not be assembled into an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric device must be greater than the outer diameter of the stem valve.
For part of the rotary valve and the multi-rotary valve in the dark rod valve, although do not have to consider the valve rod diameter through the problem, but in the selection should also fully consider the stem diameter and the size of the keyway, so that the assembly can work normally. Output speed valve opening and closing speed if too fast, easy to produce water hammer phenomenon.
Therefore, according to the different conditions of use, the appropriate opening and closing speed should be selected The valve electric actuator has its special requirements, that is, it must be able to limit the torque or axial force. Usually the valve electric actuator adopts a connecting shaft device that limits the torque. When the specifications of the electric device are determined, the control torque is determined. Generally operating within a predetermined period of time, the motor will not overload. However, if the following conditions can lead to Overload: First, the power supply voltage is low, can not get the required torque, so that the motor stop turning, the second is to incorrectly adjust the torque limiting mechanism, so that it is greater than the stop torque, resulting in continuous generation of large torque, so that the motor stop turning; third, intermittent use, resulting in heat savings
Exceeding the allowable temperature appreciation of the motor; four is due to some reason torque limit mechanism circuit failure, so that the torque is too large; Five is the use of ambient temperature is too high, relative to reduce the thermal capacity of the motor. In the past, the motor protection method is the use of fuses, overcurrent relays, thermal relays, thermostats, etc., but these methods have their own advantages and disadvantages. There is no absolute and reliable way to protect this variable load equipment for electric devices. Therefore, it is necessary to adopt a variety of combinations, summed up there are two kinds: first, the increase and decrease of the input current of the motor to judge, the second is to judge the heat of the motor itself.
Both of these methods, regardless of the type of motor thermal capacity, should be considered for a given time margin.
In general, the basic protection methods of overload are: overload protection for continuous operation or point operation of the motor, the use of thermostats, the protection of motor plugging, the use of thermal relays, and the use of fuses or overcurrent relays for short-circuit accidents. On the distribution of valve market, mainly according to the construction of engineering projects, the largest users of valves are petrochemical industry, power sector, metallurgical sector, chemical industry and urban construction departments. The petrochemical industry mainly uses API standard gate valves, Globe valves and check valves; The Power department mainly adopts high temperature pressure gate valve, globe valve, check valve and safety valve and part of the water supply and drainage valve of low pressure butterfly valve, gate valve, chemical industry mainly uses