Question

List the different actuators. Explain any two types of actuators with advantages and disadvantages

Answer 1

Actuators

[1] Hydraulic Actuator

[2] Electrical Actuator

[3] Pneumatic Actuator

[4] Mechanical Actuator

Hydraulic Actuator

According to Pascal, when there is an increase in pressure at any point in a confined incompressible fluid, then there is an equal increase at every point in the container. Hydraulic actuators are designed based on this principle (Pascal’s law). 2. To understand how hydraulic actuators works, let’s take an example of two cylinders connected together as shown in the figure. Suppose one cylinder has cross sectional area of 1 sq.cm. and the second one has cross section area of 10 sq.cm. If the cylinders are filled with incompressible fluid and 1 unit of pressure is applied to the left cylinder pushing the pump (actually liquid) by 10 cm. Then the resulting force acts on the right cylinder pushing the piston by 1 cm, but with a force of 10 units. This means applying 1 unit of force produces 10 units of force on the other side

 

Advantages of hydraulic actuators:

1. They can move moderate to heavy loads.

2. They are more efficient and deliver better performance than others.

3. Power to weight ratio of these actuators is high

Mechanical Actuator:- A mechanical actuator functions to execute movement by converting one kind of motion, such as rotary motion, into another kind, such as linear motion. An example is a rack and pinion. The operation of mechanical actuators is based on combinations of structural components, such as gears and rails, or pulleys and chains. 

Advantages:-

[1] Simple in construction

[2] Reliable

Disadvantages:-

[1] Slightly lower efficiency compare to other

[2] Frequent Maintenance required

Pneumatic Actuator

 Energy, in the form of compressed gas, is converted into linear or rotary motion, depending on the type of actuator. Pneumatic energy is more desirable for main engine controls because it can quickly respond in starting and stopping as the power source does not need to be stored in reserve for operation. Also, pneumatic actuators are preferred in places where cleanliness is important, since the fluid in hydraulic actuators might leak and contaminate the surroundings. They are employed where fast cycles are required

Advantages

[1] Maintenance cost is low

[2] Require less floor space.

[3] Less Expensive.

Disadvantages

[1] They are less efficient.

[2] Comparatively poor performance. 

Electric Actuators 

Electric actuators are devices powered by motors that convert electrical energy to mechanical torque. The electrical energy is used to create motion in equipment that require multi-turn valves like gate or globe valves. Since no oil is involved, electrical actuators are considered to be one of the cleanest and readily available forms of actuators. Electric actuators are typically installed in engines, where they open and close different valves. There are many designs of electric actuators and this depends on their function in the engine that they are installed in.

Advantages

[1] They are used to carry higher loads

[2] More efficiency

Disadvantages

[1] Requires more power

[2] Possibilities of fire hazards / accidents