Question

Research and discuss the similarities and dissimilarities of several types of PLCs, i.e. pneumatic, hydraulic and electric. Include in your discussion examples of each and situations where one type is better used than the other. Your comments should be 100 words or more and include a citation.

Answer 1

The difference between Pneumatic, Hydraulic and Electrical Actuators:

An actuator moves or controls loads and mechanisms; the actuator is operated by energy namely either pressurised fluid, air or electricity, sourced by utilising a pneumatic, hydraulic or electric pump.
The energy is then converted into a motion or force to achieve movement or control.

Pneumatic linear actuators consist of a piston inside a hollow cylinder. Pressure from an external compressor or pneumatic pump moves the piston inside the cylinder, as pressure increases, the cylinder moves along the axis of the piston, creating a linear force. The piston returns to its original position by either a spring back force or fluid being supplied to the other side of the piston.

Hydraulic linear actuators operate similarly to pneumatic actuators, but an incompressible liquid from a pump rather than pressurized air is what moves the cylinder.

An electric linear actuator converts electrical energy into torque. A mechanically connected electric motor turns a lead screw; a threaded lead or ball nut with corresponding threads that match those of the screw is prevented from rotating with the screw. When the screw rotates, the nut gets driven along the threads, the direction the nut moves in depends on which direction the screw rotates.

Pneumatic actuators

Advantages

The benefits of pneumatic actuators come from their simplicity.

Pneumatic actuators’ typical applications involve areas where the conditions involve extreme temperatures, a typical temperature range is -40°F to 250°F.

In terms of safety and inspection, using air and pneumatic actuators avoids using hazardous materials. They also meet explosion protection and machine safety requirements because they create no magnetic interference due to the lack of motors.

Pneumatic actuators are also lightweight, require minimal maintenance, and have durable components that make pneumatics a cost effective method of power.

Disadvantages

Pressure losses and compressibility of air make pneumatics less efficient than other methods. Compressor and air delivery limitations mean that operations at lower pressures will have lower forces and slower speeds.

To be truly efficient, pneumatic actuators must be sized for a specific job. Hence, they cannot be used for other applications.

Even though air is readily available, it can be contaminated by oil or lubrication, leading to downtime and maintenance. Companies still have to pay for compressed air, making it a consumable, along with the compressor and line maintenance costs.

Hydraulic actuators

Advantages

Hydraulic actuators are rugged and suited for high force applications. They can produce forces 25 times greater than pneumatic cylinders of equal size. They also operate in pressures of up to 4,000 psi.

A hydraulic actuator can hold force and torque constant without the pump supplying more fluid or pressure due to the incompressibility of fluids.

Hydraulic actuators can have their pumps and motors located a considerable distance away with minimal loss of power.

Disadvantages

Hydraulics will leak fluid. Like pneumatic actuators, loss of fluid leads to less efficiency and cleanliness problems resulting in potential damage to surrounding components and areas.

Hydraulic actuators require many complementary parts, including a fluid reservoir, motor, pump, release valves, and heat exchangers, along with noise reduction equipment.

Electrical actuators

Advantages

Electrical actuators offer the highest precision control positioning. Their setups are scalable for any purpose or force requirement, and are quiet, smooth, and repeatable.

In terms of noise, they are quieter than pneumatic and hydraulic actuators and because there are no fluids leaks, environmental hazards are eliminated.

Disadvantages

Electrical actuators are not suited for all environments, unlike pneumatic actuators, which are safe in hazardous and flammable areas.