Understanding of electric valves
Simply put, the electric valve is to use an electric actuator to control the valve, so as to realize the opening and closing of the valve. It can be divided into upper and lower parts, the upper part is the electric actuator, and the lower part is the valve. Electric valve device is an indispensable device for valve program control, automatic control and remote control. Its movement process can be controlled by stroke, torque or axial thrust. Since the working characteristics and utilization of electric valve devices depend on the type of valve, the working specifications of the device and the position of the valve on the pipeline or equipment, the correct selection of the electric valve device can prevent overloading (the working torque is higher than the control Torque) is critical.
Generally, the correct selection of electric valve device is based on the following:
Operating torque Operating torque is the main parameter for selecting an electric valve device, and the output torque of the electric device should be 1.2 to 1.5 times the valve operating torque.
There are two main structures for operating the thrust electric valve device: one is without a thrust plate, and the torque is directly output; the other is with a thrust plate, and the output torque is converted into output thrust through the stem nut in the thrust plate.
Number of rotations of the output shaft The number of rotations of the output shaft of the electric valve device is related to the nominal diameter of the valve, the pitch of the stem, and the number of thread heads. It should be calculated as M=H/ZS (M is the total rotation circle that the electric device should meet H is the opening height of the valve, S is the thread pitch of the valve stem drive, and Z is the number of stem thread heads).
If the opening and closing speed of the output speed valve is too fast, water hammer will easily occur. Therefore, the appropriate opening and closing speed should be selected according to different conditions of use. Electric valve devices have special requirements, that is, they must be able to limit torque or axial force. Usually electric valve devices use torque-limiting couplings. When the specifications of the electric device are determined, the control torque is also determined. Generally run within a predetermined time, the motor will not be overloaded.
However, overload may result in the following situations:
First, the power supply voltage is low and the required torque cannot be obtained, which makes the motor stop rotating;
The second is to set the torque limit mechanism by mistake to make it larger than the stopping torque, causing continuous excessive torque and stopping the motor;
The third is intermittent use, and the heat accumulation generated exceeds the allowable temperature rise of the motor;
Fourth, the circuit of the torque limiting mechanism fails due to some reason, which makes the torque too large;
Fifth, the use environment temperature is too high, which relatively reduces the thermal capacity of the motor.