Hydraulic Actuators: The Transmitter

Unit - 2

Hydraulic Actuators and Control Components

Chapter 5: Hydraulic Actuators: The Transmitter

Chapter 6: Control Components (Hydraulic Valves)

Chapter 7: Fluid Power Symbols

Chapter: 5

Hydraulic Actuators:

The Transmitter

"Few people think no more than two or three times a year; I have made an international_reputa- tion for myself by thinking once a week."

– George Bernard Shaw

"Perfection consists not in doing extraordinary things, but in doing ordinary things extraordi- narily well."

- Angelique Arnauld

"The pessimist sees difficulty in every opportunity. The optimist sees the opportunity in every difficulty."

- Winston Churchill

Learning Objectives

While reading and after studying this chapter, you will be able to:

• Understand and appreciate the principle and uses of actuators.

• Identify and describe the construction and operation of various types of hydraulic cylinders.

• Distinguish between a single-acting and a double- acting hydraulic cylinders.

• Appreciate the mechanism and purpose of a cylinder cushion.

• Describe the operation and features of tandem, telescopic, and double-rod cylinders.

• Understand the function of a hydraulic motor and differentiate it with a hydraulic cylinder.

• Explain the construction and operation of vane, and piston type hydraulic motors. gear,

• Understand the principle of a limited rotation hydraulic cylinders.

• Evaluate the hydraulic motors' performance and to determine the design torque and power delivered hydraulic motors.

1. INTRODUCTION

We know that the hydraulic pumps convert the mechanical energy into hydraulic energy. In many fluid power applications, we need to convert the pressure energy of liquid (called Hydraulic energy) into mechanical energy to perform useful work. This function is accomplished by the devices known as actuators. Thus actuators are the devices used for converting hydraulic energy into mechanical energy, and therefore have a function opposite to that of pumps. Actuators can be used to produce linear, rotary, or oscillation motion in a hydraulic system.

In this chapter, we shall discuss the principle, construction, operation, and application of various hydraulic actuators and motors employed in a hydraulic system.

1. What are Actuators ?

• Actuators are the devices used for converting hydraulic energy into mechanical energy.

• In other words, actuators perform a function just opposite to that of the pumps.

• The pressurized hydraulic fluid delivered by the hydraulic pump is supplied to the actuators, which converts the energy of the fluid into mechanical energy. This mechanical energy is used to get the work done:

• The hydraulic actuators produce linear, rotary, or oscillating motion.

• They can be used for lifting, tilting, clamping, opening, closing, metering, mixing, turning, swinging, counterbalancing, bending and for many other operations.

• Special applications are on roll-over devices, conveyors, valve operators, printing presses, rock drills, dies, clamps, machine tools, etc.

2. Types of Hydraulic Actuators

Based on the type of motion actuators produce, they are categorized into two :

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

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

(a) Continuous rotary actuators (or simply hydraulic motors), and

(b) Limited-rotation rotary actuators (also called 'oscillation fluid motors').

The linear actuators generate motion in a straight line to perform the work. The rotary actuators generate rotary output motion to perform the work.