Valve actuators refer to devices that provide linear or rotary movement of the valve, which using liquid, gas, electricity or other energy sources and converted it by motors, cylinders or other devices.
Pneumatic actuator uses air pressure to realize the valve drive open and close or regulation with one piece implementation and regulation mechanism, can be divided into the membrane, piston and rack and pinion pneumatic actuator. The pneumatic valve structure is simple, easy to operate and check, can also easily achieve the positive reaction of the exchange, more economical than electric and hydraulic. It is widely used in power plant, chemical industry, oil refining and other production processes with high safety requirements.
Electric actuator has a large torque, simple structure and easy to maintenance, can be used to control air, water, steam and corrosive media like mud, oil, liquid metal, radioactive media and other types of fluid flow. It also has good stability, constant thrust and good anti-deviation ability. Its control accuracy is higher than the pneumatic actuator and can well overcome the imbalance of medium, mainly used in power plants or nuclear power plants.
When selecting a valve actuator, it is necessary to know the type of valve, torque size and other issues. Generally in the term of the structure, reliability, cost, output torque and other terms to consider. Once the actuator type and the drive torque required for the valve are determined, the actuator manufacturer’s data sheet or software can be used for selection. Sometimes the speed and frequency of valve operation should be considered. Here we collect some tips or suggestion for the actuators choices:
The pneumatic actuator must be used together with valve positioner and air source, and its cost is almost the same as the electric valve. In water and sewage treatment, most valve actuators are operated in on/off mode or manually. The monitoring functions of electric actuators, such as overtemperature monitoring, torque monitoring, conversion frequency and maintenance cycle, must be designed in the control and test system, which leads to a large number of line input and output. In addition to terminal position sensing and air source handling, pneumatic actuators do not require any monitoring and control functions.
Electric valves are an electric power source, circuit board or motor failure prone to spark, generally used in the environmental requirements are not high occasions. Pneumatic actuators can be used for potentially explosive occasions, and it is worth noting that the valve or valve island should be installed outside the explosion area, the pneumatic actuators used in the explosion area should be driven by trachea.
The service life
The electric actuators are suitable for intermittent operation, but not for continuous closed-loop operation. Pneumatic actuators have excellent overload resistance and are maintenance-free, requiring no oil change or other lubrication, with a standard service life of up to one million switching cycles, which is longer than other valve actuators. In addition, pneumatic components with high vibration resistance, corrosion resistant, strong and durable, even not damage at a high temperature. Electric actuators consist of a large number of components and are relatively easy to damage.
Electric actuators run slowly than pneumatic and hydraulic actuators, it takes a long time from the regulator output signal to response and movement to the corresponding position. There is a great loss of energy when the supplied energy is converted into motion. Firstly, the electric motor converts most of the energy into heat, and then it uses gears with a complex structure. Frequent regulation will easily cause the motor to overheat and generate thermal protection.
Essentially, the main difference between electric and pneumatic valves is the use of actuators and has nothing to do with the valve itself. Choose which actuator to use that depends on the operating conditions, such as a chemical application or explosion protection or wet environment where need pneumatic valve and an electric valve is ideal for large diameter piping system.