Brief Analysis of the Construction and Installation of Electric Valves

- May 29, 2018-

The electric valve has a larger force than the ordinary valve. The speed of the electric valve can be adjusted, the structure is simple, and it is easy to maintain. Due to the buffering property of the gas during the operation, it is not easy to be damaged due to jamming, but it must have a gas source and its control. The system is also more complicated than electric valves. This type of valve should generally be installed horizontally in the pipeline.

    Electric valves are usually composed of electric actuators and valves. The electric valve uses electric energy as power to drive the valve through the electric actuator to realize the valve switching action. In order to achieve the purpose of switching the pipeline medium. So, what are the details of the electric valve during installation?

The electric valve device is an indispensable device for implementing valve control, automatic control and remote control. The movement process can be controlled by the size of stroke, torque or axial thrust. Since the operating characteristics and utilization of the electric valve device depend on the type of valve, the working specification of the device and the position of the valve on the pipeline or equipment, the correct selection of the electric valve device will prevent the occurrence of overload phenomenon (the working torque is higher than the control Torque is of utmost importance. In general, the correct selection of electric valve devices is based on the following:

    Operating Torque Operating torque is the most important parameter for selecting the electric valve device. The output torque of the electric device should be 1.2 to 1.5 times the maximum torque of the valve.

    There are two types of mainframes for operating the thrust electric valve device: one is to directly output the torque without configuring the thrust plate; the other is to configure the thrust plate, and the output torque is converted into the output thrust through the stem nut in the thrust plate.

    Output shaft rotation number 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 valve stem, and the number of threads. It is calculated according to M=H/ZS (M is the total rotation that the electric device should meet. Number, H is the valve opening height, S is the valve stem transmission thread pitch, and Z is the valve stem thread head number).

    Stem Diameter For multi-rotary type stem valves, if the maximum valve stem diameter allowed by the electric device cannot pass through the stem of the valve with which it is fitted, it cannot be assembled into an electric valve. Therefore, the inner diameter of the hollow output shaft of the electric device must be larger than the outer diameter of the stem of the stem valve. For the rotary valve and the multi-rotary valve, although the stem diameter does not have to be taken into consideration, the diameter of the stem and the size of the key groove should be fully taken into consideration during the selection, so that the assembly can work normally.

    If the speed of opening and closing of the output speed valve is too fast, water hammer may easily occur. Therefore, the appropriate opening and closing speed should be selected according to different conditions of use.

    The electric valve device has its special requirement that it must be able to limit the 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 determined. Generally run within a predetermined time, the motor will not be overloaded. However, the following conditions may lead to overload: First, the power supply voltage is low, the required torque is not available, so that the motor stops rotating; second, the torque limiting mechanism is incorrectly set to be greater than the stopping torque, Caused by continuous generation of excessive torque, so that the motor stops rotating; Third, intermittent use, resulting in heat accumulation, exceeding the allowable temperature rise of the motor; Fourth, for some reason torque limit mechanism circuit failure, so that torque Large; fifth is the use of high ambient temperature, relative to the thermal capacity of the motor.

    The way to protect the motor in the past was to use fuses, overcurrent relays, thermal relays, thermostats, etc., but these methods have advantages and disadvantages. For electric devices such as variable load equipment, absolutely reliable protection methods are not available. Therefore, we must take various combinations, summed up in two ways: one is to judge the increase or decrease of the motor input current; the second is to determine the heat of the motor itself. Both of these methods, regardless of the kind, must take into consideration the time margin given by the thermal capacity of the motor.

    In general, the basic methods of overload protection are: overload protection for continuous operation or jog operation of the motor, use of a thermostat; use of thermal relays for protection against stalling of the motor; use of fuses or overcurrent relays for short circuit accidents.