Hydraulic Fluids and their Properties

Chapter: 2

Hydraulic Fluids and their Properties

"The first rule of any technology used in a business is that automa- tion applied to an efficient operation will magnify the efficiency. The second is that automation applied to an inefficient operation will magnify the inefficiency.”

- Bill Gates

"The important thing in science is not so much to obtain new facts as to discover new ways of thinking about them."

- Sir William Biagg

"Give me a lever long enough and a fulcrum on which to place it, and I shall move the world."

- Archimedes

Learning Objectives

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

• Appreciate the primary functions of a fluid in any fluid power system.

• Understand the difference between a liquid and a gas.

• Identify and appreciate the various properties desired of a hydraulic fluid.

• Explore the significance of each properties of fluids. 

• Examine the types of hydraulic fluids available for hydraulic systems.

• Select a better hydraulic fluid for a given application.

1. INTRODUCTION

The fluid is an essential and important component of any fluid power system. No other component of the system must perform as many functions or meet as many requirements as the fluid. The fluid must not only provide a medium for efficient power transmission, but it must also lubricate, cool, protect from corrosion, not leak excessively, and perform numerous other functions depending on the system design. There is no single fluid which can be employed for all applications. The selection of a fluid for a particular fluid power application has become a complicated and very challenging task. Thus it is necessary for the fluid power designer to have at least an elementary understanding of the terminology prevalent in the specification of fluids.

In this chapter, we shall examine the different types of fluids, and present the various properties which are important in the selection and use of fluids.

1. Functions of a Fluid in a Fluid Power System

The various functions/purposes of the fluid in a fluid power system can be summarised as shown in Table 2.1.

Table 2.1. Functions of a fluid in any fluid power system

1. To transmit power (basic purpose).

2. To lubricate moving parts.

3. To seal gaps and clearances between mating components.

4. To dissipate heat generated by internal friction.

5. To prevent rust and corrosion.

6. To remove unwanted and harmful impurities from the system.