Advantages and Disadvantages of Electric Valves versus Pneumatic Valves
Add time：2017/3/23 9:11:58 Page views：2586
Electric valve actuators are mainly applied in power plants or nuclear power plants, as high‑pressure water systems require smooth, stable and slow‑acting operation. The major advantages of electric actuators lie in high stability and constant thrust available for users. The maximum thrust generated by large‑size actuators can reach up to 225 000 kgf. Only hydraulic actuators can deliver such high thrust, yet hydraulic actuators cost considerably more than electric ones.
Electric actuators feature excellent anti‑deviation capability. Their output thrust or torque is basically constant, which can effectively counteract the unbalanced force of the medium and realize precise control of process parameters. Therefore, they offer higher control accuracy than pneumatic actuators. When equipped with a servo amplifier, forward‑reverse action switching can be easily achieved, and the valve position upon signal loss (hold / fully open / fully closed) can be conveniently configured. Upon failure, the valve will stay at its original position, which cannot be realized by pneumatic actuators. Pneumatic actuators have to rely on an integrated protection system to maintain valve position.
Main Disadvantages of Electric Actuators
They have relatively complex structures and are more prone to failures. Due to such complexity, higher technical competence is required for on‑site maintenance personnel.
Heat is generated during motor operation. Frequent modulation may cause motor overheating and trigger thermal protection, meanwhile increasing wear of reduction gears.
In addition, their operating speed is slow. A relatively long time is needed from the moment the controller sends out a signal until the control valve responds and moves to the corresponding position, which is a disadvantage compared with pneumatic and hydraulic actuators.
Pneumatic Valves
For pneumatic valve actuators, the actuator and regulating mechanism form an integrated unit. There are two types of actuators: diaphragm type and piston type. The piston type provides long stroke and is suitable for applications requiring large thrust; the diaphragm type has a short stroke and can only drive the valve stem directly. Benefiting from simple structure, large output thrust, stable and reliable operation, as well as explosion‑proof performance, pneumatic actuators are widely used in safety‑critical production processes such as power plants, chemical plants and oil refineries.
Main Advantages of Pneumatic Actuators
‑ Accept continuous pneumatic signals and output linear displacement (continuous electric signals can also be accepted with an electro‑pneumatic converter). Some models can output angular displacement when fitted with a rocker arm.
‑ Support forward‑action and reverse‑action functions.
‑ High moving speed; speed decreases as load increases.
‑ Output force is related to operating pressure.
‑ High reliability, yet the valve cannot maintain its position when air supply fails (position can be maintained with a position‑holding valve).
‑ Difficult to realize segmented control and program control.
‑ Simple overhaul and maintenance, good environmental adaptability.
‑ Relatively high output power.
‑ Explosion‑proof capability.
Company News
Chinese
English
