How to choose electric actuators and pneumatic actuators

How to choose the true actuators

1. Key Considerations for Actuator Selection
①Reliability;
②Economy;
③Smooth action and sufficient output torque;
④Simple structure and easy maintenance.

2. Comparison of the selection of electric actuators and pneumatic actuators
(1) The pneumatic actuator is simple and reliable
The poor reliability of old-fashioned electric actuators was its consistent weakness in the past. However, in the 1990s, the development of electronic actuators completely solved this problem, which can be maintenance-free within 5 to 10 years, and its reliability even exceeds that of pneumatic actuators.

(2) Drive source
The biggest disadvantage of the pneumatic actuator is that it needs to set up a gas source station, which increases the cost; the driving source of the electric valve is available anywhere.

(3) In terms of price
Pneumatic actuators must be attached with valve positioners and air sources, and the cost is comparable to that of electric valves (imported electric valve positioners are equivalent to imported electronic actuators; domestic positioners are comparable to domestic electric actuators) .

(4) Thrust and stiffness: the two are equivalent.

(5) Fire and explosion-proof
"Pneumatic actuator + electric valve positioner" is slightly better than electric actuator.



3. Recommendations

(1) If possible, it is recommended to use imported electronic actuators with domestic valves for localization occasions, new projects, etc.

(2) Although the membrane actuator has the defects of insufficient thrust, small rigidity and large size, its structure is simple, so it is still the most used actuator at present.

(3) Note on the selection of piston actuators:

①When the thrust of the pneumatic diaphragm actuator is not enough, choose the piston actuator to increase the output force; for the regulating valve with large pressure difference (such as medium pressure steam cut-off), when the DN ≥ 200, even the double-layer piston actuator should be selected;

② For ordinary control valves, piston actuators can also be used to replace membrane actuators, which greatly reduces the size of the actuators. From this point of view, pneumatic piston control valves will be used more;

③ Diagonal stroke type regulating valve, its angular stroke actuator, the typical structure is double-piston rack and pinion rotary type. It is worth emphasizing that the traditional "straight stroke piston actuator + angle iron + crank connecting rod" method.

Second, the comparison of electric and pneumatic actuators

 
1. Anti-overload capability and service life

Electric actuators can only be used for intermittent operation and are therefore not suitable for continuous closed-loop operation. Pneumatic actuators, on the other hand, are overload-resistant and maintenance-free throughout their service life. No oil change or other lubrication is required. With a standard service life of up to one million switching cycles, pneumatic actuators are superior to other valve actuators.

2. Safety
Pneumatic actuators can be used in potentially explosive situations, especially in the following situations:

An explosion-proof valve (such as a Namur valve with a suitable coil) is required; the valve or valve island needs to be installed outside the explosion area, and the pneumatic actuator used in the explosion area must be driven by the gas pipe; the electric actuator is not easy to be used in a potential explosion hazard. and high cost.

3. Anti-overload capability
In situations where increased torque is required or special forces are required, electric actuators will quickly reach their torque limit. Especially in the case of irregular opening or closing of valve actuators for long periods of time, the advantage of the overload resistance of pneumatic actuators is obvious, since deposits or sintering can increase the starting torque. Using pneumatic components, it is easy to increase the working pressure as well as the force or torque.

4. Economical
In water and wastewater technology, most valve actuators are operated in on/off mode or are even designed for manual operation, so pneumatic components open up important prospects for rationalization. Compared with pneumatic actuators, if electric actuators are used, monitoring functions such as overtemperature monitoring, torque monitoring, switching frequency, maintenance intervals must be designed in the control and test system, which results in a large number of line inputs and outputs . Apart from end position sensing and air supply handling, pneumatic actuators do not require any monitoring and control functions. The cost of pneumatic actuators is low, so it is more important to automate manual valve actuators.

5. Assembly
Pneumatic technology is very simple. The installation of the pneumatic actuator on the valve drive head and the connection and drive of the air source processing device can be easily realized. In addition, the maintenance-free design of the pneumatic actuator ensures that it is easy to install and operate.

6. Components
Pneumatic components have high vibration resistance, are strong and durable, and are generally not damaged. Even high temperatures will not damage corrosion-resistant components. Electric actuators are composed of a large number of components, which are relatively easy to damage.

The above is the introduction of part of valves used in domestic water pipelines, hoping to help you understand the purpose and selection of valves. If you have any needs for valves, please consult us for selection services and discounted prices. [email protected]