Electric valve
Valve electric actuators are mainly used in power plants or nuclear power plants, because the high-pressure water system requires a smooth, stable and slow process. The main advantages of the electric actuator are high stability and constant thrust which can be applied by users. The maximum thrust produced by the actuator can reach 225 000 kgf. 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. The output thrust or torque is basically constant. It can overcome the unbalanced force of the medium and achieve the accurate control of the process parameters, so the control accuracy is higher than that of the pneumatic actuator. If the servo amplifier is used, the exchange of positive and negative effects can be easily realized, and the valve position of the cut-off signal can be easily set (hold/turn on/turn off). When the fault occurs, it must stay in place, which is impossible for the pneumatic actuator to do. The pneumatic actuator must rely on a set of combined protection system to achieve position preservation.
The main shortcomings of electric actuators are as follows:
The structure is more complex and easy to break down, and because of its complexity, the technical requirements for field maintenance personnel are relatively higher; motor operation needs to generate heat, if the adjustment is too frequent, it is easy to cause motor overheating, thermal protection, but also will increase the wear of gear reducer; the other is running slowly. It takes a long time to output a signal from the regulator and move to the corresponding position in response to the regulator valve, which is inferior to the pneumatic and hydraulic actuators.
Pneumatic Valve
The actuating mechanism and regulating mechanism of valve pneumatic actuator are unified as a whole. The actuating mechanism of valve pneumatic actuator includes membrane type and piston type. The piston stroke is long and suitable for situations requiring greater thrust, while the membrane stroke is small and can only drive the valve stem directly. Pneumatic actuator has many advantages, such as simple structure, large output thrust, stable and reliable movement, and safety and explosion-proof. It is widely used in power plants, chemical industry, refinery and other production processes with high safety requirements.
The main advantages of pneumatic actuators are as follows:
Accept the continuous gas signal, output linear displacement (power/gas conversion device, can also accept continuous electrical signal), and some with rocker arm, can output angular displacement.
It has positive and negative functions.
It moves faster, but slows down as the load increases.
The output force is related to the operating pressure.
Reliability is high, but the valve can not be maintained after the interruption of the gas source (with a reserve valve can be maintained).
It is inconvenient to realize subsection control and program control.
Maintenance is simple and adaptable to the environment.
The output power is large.
It has explosion-proof function.
