Electric valve construction and installation details electric valve and pneumatic valve advantages and disadvantages of comparison

Electric valve construction and installation details electric valve and pneumatic valve advantages and disadvantages of comparison

The electric valve action pitch is larger than the ordinary valve, the electric valve switch action speed can be adjusted, simple structure, easy to maintain, the process of action because of the buffer characteristics of the gas itself, not easy to be damaged by jamming, but must have the air source, and its control system is more complex than the electric valve. This type of valve should generally be installed horizontally in the pipeline.

Electric valve usually consists of electric actuator and valve. Electric valve uses electric energy as power to drive the valve through the electric actuator to realize the valve switch action. So as to achieve the purpose of switching the pipeline medium. So, what details should we pay attention to in the installation process of the electric valve?

Electric valve device is an indispensable equipment to realize valve program control, automatic control and remote control. Its motion process can be controlled by stroke, torque or the size of axial thrust. Because the working characteristics and utilization rate of the electric valve device depend on the type of valve, the working specification of the device and the position of the valve in the pipeline or equipment, therefore, the accurate selection of the electric valve device is crucial to prevent the overloading phenomenon (the working torque is higher than the control torque). Usually, the accurate selection of electric valve device based on the following:

Operating torque The operating torque is the main parameter for selecting the electric valve device. The output torque of the electric device should be 1.2 ~ 1.5 times of the torque of the valve operating tripod.

There are two main structure of the thrust electric valve device: one is not configured with thrust disc, direct output torque; The other is the configuration of thrust disc, the output torque through the thrust disc stem nut into the output thrust.

The number of rolling rings of the output shaft of the electric valve device is related to the nominal diameter of the valve stem pitch and the number of threads. It should be calculated according to M=H/ZS (M is the total number of rolling rings that the electric device should be satisfied with, H is the opening height of the valve, S is the pitch of the valve stem drive thread and Z is the number of the valve stem thread).

Stem diameter for multi-turn open-rod valves, if the large stem diameter agreed by the electric device can not pass through the valve stem, 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 of the open-rod valve. For the dark rod valves in the department rotary valves and multi-rotary valves, although it is not necessary to consider the diameter of the valve stem, the diameter of the valve stem and the size of the key way should also be fully considered in the selection, so that the assembly can work normally.

If the opening and closing speed of the output speed valve is too fast, it is easy to produce water percussion phenomenon. Therefore, the appropriate opening and closing speed should be selected according to different use conditions.

Comparison of advantages and disadvantages of electric valve and pneumatic valve

Valve electric actuators are mainly used in power plants or nuclear power plants, as high pressure water systems require a smooth, non-chaotic and slow process. The main advantages of the electric actuator are that the height is not messy and the user can apply a constant thrust. The thrust generated by the large actuator can be as high as 225000kgf. Only the hydraulic actuator can achieve such a large thrust, but the cost of the hydraulic actuator is much higher than that of the electric actuator. The anti-deviation ability of the electric actuator is very good, and the output thrust or torque is basically constant, which can well overcome the unbalanced force of the medium and achieve the correct control of the process parameters. Therefore, the control accuracy is higher than that of the pneumatic actuator. If the servo amplifier is used, the positive and negative effects can be easily exchanged, and the position state of the break signal valve can be easily set (keep/fully open/fully closed). When the fault occurs, it must stay in the original position, which is not possible for the pneumatic actuator. The pneumatic actuator must use a set of combined protection system to realize the position preservation.

The main disadvantages of electric actuator are:

The structure is more complex, more prone to failure, and because of its complexity, the technical requirements for on-site maintenance staff are relatively high; Motor operation to generate heat, if the adjustment is too frequent, easily cause motor overheating, thermal protection, but also increase the wear of the reduction gear; In addition, the operation is slow. It takes a long time to output a signal from the regulator to the corresponding position in response to the regulator. This is why it is not as good as the pneumatic and hydraulic actuators.

Air operated valve

The actuator and the regulating mechanism of the valve pneumatic actuator are the same whole, and the actuator has two categories: film type and piston type. The piston stroke is long, suitable for the occasion of requiring a larger thrust; The film stroke is small, can only directly drive the stem. Because the pneumatic actuator has the advantages of simple structure, large output thrust, stable and reliable action, and safety and explosion-proof, it has the perfect application in the production process of power plant, chemical industry, oil refining and other safety requirements.

The main advantages of pneumatic actuator:

Accept continuous gas signal, output linear displacement (after adding electric/gas conversion device, can also accept continuous electrical signal), some equipped with rocker arm, can output angular displacement.

It has positive and negative function.

The movement speed is high but slows down as the load increases.

The output force is related to the operating pressure.

High reliability, but the valve cannot be maintained after the air supply is interrupted (it can be maintained after adding the retaining valve).

Inconvenient to achieve subsection control and program control.

Inspection and maintenance simple, good adaptability to the environment.

The output power is large.

With explosion-proof function.