review and summary

REVIEW AND SUMMARY

• The actuators are the devices used for converting hydraulic energy into mechanical energy, and therefore have a function opposite to that of pumps.'

• Types of hydraulic actuators: Based on the type of motion actuators produce, they are categorized into :

1. Linear actuators (also called 'hydraulic cylinders'), and

2. Rotary actuators (also called 'hydraulic motors').

(a) Continuous rotary actuators, and

(b) Limited-rotation rotary actuators.

• The hydraulic actuators can be used for lifting, tilting, clamping, opening, closing, metering, mixing, turning, swinging, counter balancing, bending, and for many other operations.

• The hydraulic cylinder is a device that converts fluid power into linear mechanical force and motion.

• The important types of hydraulic cylinders are :

1. Single-acting cylinders,

2. Double-acting cylinders,

3. Telescopic cylinders,

4. Tandem cylinders,

5. Dual linear cylinders, and

6. Through rod cylinders.

• The construction, working, advantages, disadvantages, applications and ranges of the above-mentioned hydraulic cylinders have been discussed in this chapter.

• The function of a rotary actuator (also known as hydraulic motor) is to convert hydraulic energy into rotary mechanical energy.

• The hydraulic motors are very much identical in construction and size to rotary type pumps. They work on exactly the reverse principle to that of rotating pumps.

• Types of hydraulic motors: The hydraulic motors can be classified based on their degree of angular movement as :

1. Continuous rotary hydraulic motors, and

(a) Gear motors, (b) Vane motors, and (c) Piston motors.

2. Limited-rotation hydraulic motors.

(a) Vane type, and (b) Piston type.

•  Formulae Summary:

For double-acting cylinders:

For single-vane type limited-rotation motor : 

For hydraulic motors :

KEY TERMS ONE SHOULD REMEMBER

Actuators

Hydraulic actuators 

Linear actuator 

Hydraulic cylinders

Single-acting cylinders 

Double-acting cylinders

Differential cylinders

Telescopic cylinders

Tandem cylinders

Dual linear cylinders 

Through rod cylinders 

Double-rod cylinders

Cylinder cushioning

Rotary actuators

Hydraulic motors

Continuous rotary hydraulic motors

Gear motors

Vane motors

Piston motors

Axial-piston motors

Radial-piston motors

Limited-rotation hydraulic motors

Vane type

Hydraulic motor performance 

Volumetric efficiency 

Mechanical efficiency

Overall efficiency

Hydraulic power

Brake power

Hydraulic motor performance

curves

Fluid transmission device

Piston type