The power source of electric valve actuators is power supply. Sparks may easily occur in case of failures of circuit boards or motors. Therefore, they are generally applied in non‑hazardous locations with low environmental requirements.
Comparing the regulating performance of pneumatic actuators and electric actuators, pneumatic actuators feature faster response speed and are more suitable for regulating working conditions. For this reason, manufacturers of control valves also produce supporting pneumatic actuators.
Electric actuators deliver relatively slow regulating response. Taking ROTORK as an example, the modulating‑type actuator can only achieve 1 200 modulation cycles per hour. Consequently, pneumatic actuators are more widely adopted for control valves compared with electric actuators.
The essential difference between electric valves and pneumatic valves lies in their different driving devices, namely actuators, whereas the control valve body itself shows no substantial difference. The selection of matching actuators mainly depends on working‑condition requirements. For explosion‑proof applications such as in the chemical industry, pneumatic valves are the dominant choice owing to high‑safety requirements and cost advantages. Equipped with smart positioners, they can connect to field buses and feature simple control modes.
Pneumatic valves provide larger actuation torque than electric valves. Their opening‑closing speed is adjustable. They feature simple structure and easy maintenance. Thanks to the cushioning property of gas, they are less prone to damage caused by jamming during operation. Nevertheless, a compressed‑air supply is mandatory, and its control system is more complicated than that of electric valves. Pneumatic valves are sensitive in response, safe and reliable. Many plants with stringent control requirements build dedicated compressed‑air stations for pneumatic instrument control components. The power source of a pneumatic valve actuator is compressed air supplied by an air compressor. A positioner converts electric control signals into pneumatic control signals to drive the pneumatic actuator for valve‑position modulation.
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