TAILIEUCHUNG - Chapter one Introductinon about Hydraulic and Pneumatic

The transmission and control of power by means of fluid under pressure is becoming in creasingly used in all branches of industry. Pneumatics deal with the use of compressed air as the fluid whilst hydraulic power covers the use of oils and other liquids. | CHAPTER ONE INTRODUCTION The transmission and control of power by means of fluid under pressure is becoming increasingly used in all branches of industry. Pneumatics deal with the use of compressed air as the fluid whilst hydraulic power covers the use of oils and other liquids. Pneumatics are generally used when relatively low forces up to 10 kN 1 ton and fast cycling speeds are wanted. Where high forces precision speed control and high power weight ratios are needed hydraulic systems are used. Fluid power is a term covering both pneumatic and hydraulic power. Applications of hydraulic power range from car jacks to hospital beds from presses exerting forces of thousands of tonnes to robots with accuracies measured in micrometers. HYDRAULIC PRINCIPLES Properties of fluids A fluid covers both liquids and gases and is a substance in which the molecules can move about with freedom. A gas is a fluid which will expand to completely fill the available space its density varies considerably with its temperature and pressure. A liquid is a fluid which will flow under gravity to take up the shape of the containing vessel in such a way that it reduces its potential energy to a minimum. The density of a liquid changes only very slightly with changes in temperature and pressure. Units There are many systems of units currently in use the three most popular being 1 the Metric System based on meter kilogram and second 2 the Imperial System using the foot pound second and 3 the SI System using meter newton second as a base. Table gives a comparison of some of the more common quantities in the three systems of unit. Pressure of a liquid Pressure is the force per unit area . Pressure Force Area Table Currently used systems of units. Quantity Symbol System SI System Imperial System Metric System Length I meter m 1 m in 1 m ft micron Ịiva 1 xm 10-6 m inch in 1 in m foot ft 1 ft in centimeter cm 1 cm 10 2 m millimeter mm 1 mm 10

• Cơ khí - Chế tạo máy
• Introductinon about Hydraulic
• Hydraulic and Pneumatic
• Flow of a fluid
• Pressure of a liquid
• Hydraulic force transmission
• Pressure head of a liquid