Valve actuators are mechanized mechanical gadgets fit for modifying the situation of different kinds of valves. The actuator itself is a component driven by an outer power source to create a specific movement, which controls the valve position. The movement produced by the actuator can be either direct (straight flat or vertical movement) or rotational (spinning around a fixed hub).
The essential difference between a pneumatic actuator and an electric actuator is the primary source of power controlling the motion of actuators. In pneumatic actuators, the source of power is air or gas that brings about the desired motion which in turn controls the valve.
In the most common type of pneumatic actuator, the diaphragm actuator, air is pumped into a hollow casing where it acts upon a diaphragm to deflect it from its said position. The diaphragm is connected to a stem that pulls and pushes a disc to control fluid flow and generate linear motion. The pneumatic actuators generally produce linear motion but can also be made to generate rotary motion.
Electric Actuators use electricity as the main power source to generate motion in the actuators. Electric Actuators are further classified into solenoid or motor-driven actuators. In solenoid driven actuators, an electric current is passed through a coil which generates a magnetic field and is used to drive the stem assembly to move the disc up and down or sideways. Motor driven actuators use A/C or D/C power source to move the stem that controls disc operation and motor driven actuators or electric actuators can produce either linear or rotary motion.
Pneumatic actuators are capable of producing the most biggest closing forces of all actuator types with some actuators with a pressure rating of 250 psi can generate forces of up to 40,000 lbs. The speeds of closing reach 2 m/s which are relatively fast closing speeds with electric type of actuators. Both the speed and force of actuator could be appropriately enabled by fine tuning a pressure relief valve or adjusting a flow regulator.
Another principal advantage of pneumatic actuators is their relative low cost per unit which allows for easy upgradation to larger lengths and larger air compressors are persistent and economical with powering several pneumatic devices at a time.
The pneumatic actuators are relatively safe , clean in operation, lack a source of ignition and hence highly reliable to put them to use in I. C engines, pumps and ventilation systems in highly inflammable areas.
Electric Actuators can be positioned relatively easily with pre-programmed halts and start positions at any predestined input. The electric actuators have speeds of 10 m/s, fastest among all types of actuators. The distancing of electric power source from the main actuator assembly keeps operations relatively safe and gives in to easier maintenance of actuator components thus minimizing replacement costs.
Electric actuators make less noise in operation as compared to other actuator types, with these models finding persistent use in noise sensitive environments.
Electric actuators are used in heavy-duty machinery and equipment such as forklifts, excavators and dump trucks. Factory robotics and other manufacturing automations require lighter-duty electric actuators.
Pneumatic Actuators produce linear motion but also can produce rotary movement. Electric Actuators use electricity to drive the actuator motion. Motor-driven Actuators are a subset of electric actuators and are powered by A/C or D/C source.