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System maintenance The most practical pneumatic actuators utilize an air pressure supply of 40 to psi 3 to 8 bar. Generally they are sized for a supply pressure of 60 to 80 psi 4 to 6 bar.
Higher are air pressure is usually difficult to guarantee and lower pressures require a very large diameter piston or diaphragm to generate desirable torque. Electric actuators are often used with a VAC power supply but are available with a wide variety of AC and DC motors in single phase and three phase.
Both pneumatic and electric actuators may be used in a wide temperature range. If control accessories are used limit switches, solenoid valves etc.
In low-temperature applications the quality of the supply air in relation to dew point should be considered. Dew point is the temperature at which condensation occurs in air. Condensate may freeze and block air supply Rotary electro motors case making the actuator inoperable.
When used outdoors an electric actuator should be sealed from the environment to prevent the introduction of moisture to the internal workings. Condensation may still form inside, if drawn from the power supply conduit, which may have captured rainwater prior to installation.
Also, since motors warm the inside of the actuator enclosure when it is operating and cools it when it is not, temperature fluctuations may cause environmental "breathing" and condensation.
For this reason all electric actuators used outdoors should be fitted with a heater. It is sometimes difficult to justify the use of electric actuators in a hazardous environment, but if compressed air is not available or if a pneumatic actuator will not provide the operating characteristics required, then an electric actuator with a properly classified enclosure may be used.
On the other hand, pneumatic actuators are inherently explosion-proof. When electric controls are used with pneumatic actuators in hazardous areas they are generally more cost effective then electric actuators.
Solenoid-operated pilot valves may be mounted and powered in a non-hazardous are and piped to the actuator. Also, reasonably priced hazardous area qualified solenoid valves are readily available.
The inherent safety of pneumatic actuators in hazardous areas makes them a practical choice in these applications. Another safety accessory widely specified in the process industries on valve actuators is the spring-return fail-safe option.
Upon power or signal failure a spring-return actuator drives the valve to a pre-determined safe position. This is a practical and inexpensive option with pneumatic actuators and is an important reason for the wide use of pneumatic actuators throughout the industry.
Where springs are not practical because of actuator size or weight, or if a double-acting unit is already installed, an accumulator tank may be installed to store air pressure.
Electric actuators are not widely available in a spring-return version; however, a battery back up system is an elegant solution. To accomplish the spring-return function an electro-hydraulic actuator is often a good choice. Electro-hydraulic actuation is achieved by energizing a hydraulic pump, which pressurizes a spring-return cylinder.
Upon power failure the spring action drives the actuator to the original position. Because only an electric power supply is required for this self-contained unit it is a practical approach to fail-safe electric valve actuation. Before specifying a pneumatic or electric actuator for valve automation it is important to consider a few of the key performance characteristics of each.
Pneumatic actuators have a percent duty cycle. In fact, the harder they work, the better they work. Electric actuators are most commonly available with 25 percent duty cycles motors.Find great deals on eBay for used rotary. Shop with confidence. An electric motor is an electrical machine that converts electrical energy into mechanical nationwidesecretarial.com electric motors operate through the interaction between the motor's magnetic field and winding currents to generate force in the form of nationwidesecretarial.comic motors can be powered by direct current (DC) sources, such as from batteries, motor vehicles or .
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Advances in transducer logic and control capabilities have resulted.
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