Learning Objectives
Upon completion of this chapter, the student should be able to:

• Explain the meaning of fluid power.
• List the various applications of fluid power.
• Differentiate between fluid power and transport systems.
• List the advantages and disadvantages of fluid power.
• Explain the industrial applications of fluid power.
• List the basic components of the fluid power.
• List the basic components of the pneumatic systems.
• Differentiate between electrical, pneumatic and fluid power systems.
• Appreciate the future of fluid power in India.

1.1 Introduction

In the industry we use three methods for transmitting power from one point to another. Mechanical transmission is through shafts, gears, chains, belts, etc. Electrical transmission is through wires, transformers, etc. Fluid power is through liquids or gas in a confined space. In this chapter, we shall discuss a structure of hydraulic systems and pneumatic systems. We will also discuss the advantages and disadvantages and compare hydraulic, pneumatic, electrical and mechanical systems.

1.2 Fluid Power and Its Scope

Fluid power is the technology that deals with the generation, control and transmission of forces and movement of mechanical element or system with the use of pressurized fluids in a confined system. Both liquids and gases are considered fluids. Fluid power system includes a hydraulic system (hydra meaning water in Greek) and a pneumatic system (pneuma meaning air in Greek). Oil hydraulic employs pressurized liquid petroleum oils and synthetic oils, and pneumatic employs compressed air that is released to the atmosphere after performing the work.

Stationary hydraulics: Stationary hydraulic systems remain firmly fixed in one position. The characteristic feature of stationary hydraulics is that valves are mainly solenoid operated. The applications of stationary hydraulics are as follows:

Production and assembly of vehicles of all types.

• Lifting and conveying devices.
• Metal-forming presses.
• Plastic machinery such as injection-molding machines.
• Rolling machines.
• Lifts.
• Food processing machinery.
• Automatic handling equipment and robots.

Mobile hydraulics: Mobile hydraulic systems move on wheels or tracks such as a tower crane or excavator truck to operate in many different locations or while moving. A characteristic feature of mobile hydraulics is that the valves are frequently manually operated. The applications of mobile hydraulics are as follows:

• Automobiles, tractors, aeroplanes, missile, boats, etc.
• Construction machinery.
• Tippers, excavators and elevating platforms.
• Lifting and conveying devices.
• Agricultural machinery.

1.3 Basic Components of a Hydraulic System

Hydraulic systems are power-transmitting assemblies employing pressurized liquid as a fluid for transmitting energy from an energy-generating source to an energy-using point to accomplish useful work. Figure 1.1 shows a simple circuit of a hydraulic system with basic components.

Figure 1.1 Components of a hydraulic system

Functions of the components shown in Fig. 1.1 are as follows:
The hydraulic actuator is a device used to convert the fluid power into mechanical power to do useful work. The actuator may be of the linear type (e.g., hydraulic cylinder) or rotary type(e.g., hydraulic motor) to provide linear or rotary motion, respectively.

1. The hydraulic pump is used to force the fluid from the reservoir to rest of the hydraulic circuit by converting mechanical energy into hydraulic energy.
2. Valves are used to control the direction, pressure and flow rate of a fluid flowing through the circuit.
3. External power supply (motor) is required to drive the pump.
4. Reservoir is used to hold the hydraulic liquid, usually hydraulic oil.
5. Piping system carries the hydraulic oil from one place to another.
6. Filters are used to remove any foreign particles so as keep the fluid system clean and efficient, as well as avoid damage to the actuator and valves.
7. Pressure regulator regulates (i.e., maintains) the required level of pressure in the hydraulic fluid.

The piping shown in Fig. 1.1 is of closed-loop type with fluid transferred from the storage tank to one side of the piston and returned back from the other side of the piston to the tank. Fluid is drawn from the tank by a pump that produces fluid flow at the required level of pressure. If the fluid pressure exceeds the required level, then the excess fluid returns back to the reservoir and remains there until the pressure acquires the required level.

1. Cylinder movement is controlled by a three-position change over a control valve.
   When the piston of the valve is changed to upper position, the pipe pressure line is connected to port A and thus the load is raised.
2. When the position of the valve is changed to lower position, the pipe pressure line is connected to port B and thus the load is lowered.
3. When the valve is at center position, it locks the fluid into the cylinder(thereby holding it in position) and dead-ends the fluid line (causing all the pump output fluid to return to tank via the pressure relief).

1.4 Objective Type Questions

Fill in the Blanks

1. Fluid power is the technology that deals with the generation, ___________and transmission of forces and movement of mechanical elements or systems.
2. The main objective of fluid transport systems is to deliver a fluid from one location to another, whereas fluid power systems are designed to perform________ .
3. There are three basic methods of transmitting power: Electrical, mechanical and_________ .
4. Only______are capable of providing constant force or torque regardless of speed changes.
5. The weight-to-power ratio of a hydraulic system is comparatively_____ than that of an electromechanical system.

1.5 State True or False
1. Hydraulic lines can burst and pose serious problems.
2. Power losses and leakages are less in pneumatic systems.
3. Pneumatic system is not free from fire hazards.
4. Hydraulic power is especially useful when performing heavy work.
5. Water is a good functional hydraulic fluid.

Thanks for joining me!

Good company in a journey makes the way seem shorter. — Izaak Walton