I – Basics of Hydraulics Unit I I – Basics of Hydraulics

Function Vs Properties of Hydraulic Fluids Introduction Function Vs Properties of Hydraulic Fluids Function Property Medium for power transfer and control Low compressibility (high bulk modulus) Fast air release Low foaming tendency Low volatility Medium for heat transfer Good thermal capacity and conductivity Sealing Medium Adequate viscosity and viscosity index Shear stability Lubricant Viscosity for film maintenance Low temperature fluidity Thermal and oxidative stability Hydrolytic stability / water tolerance Cleanliness and filterability De-miscibility Anti-wear characteristics Corrosion control

Function Property Pump efficiency Proper viscosity to minimize internal leakage High viscosity index Special function Fire resistance Friction modifications Radiation resistance Environmental impact Low toxicity when new or decomposed Biodegradability Functioning life Material compatibility

Functions of the Fluid The Hydraulic Fluid has four primary functions To transmit power To lubricate moving parts To seal clearances between parts and To cool or dissipate heat

GENERAL TYPES OF FLUIDS Classified based Properties of fluid: Ideal Fluid: A fluid which is incompressible and is having no viscosity is known as an ideal fluid. Ideal fluid is only an imaginary fluid as all the fluids, which exist, have some viscosity. Real Fluid: A fluid which possesses viscosity is known as real fluid. All fluids, in actual practice are real fluids. Newtonian Fluid: A real fluid in which the shear stress is directly proportional to the rate of shear strain is known as a Newtonian fluid. Non-Newtonian Fluid: A real fluid in which the shear stress is not proportional to the rate of shear strain  known as a Non-Newtonian fluid. Ideal Plastic Fluid: a fluid in which shear stress is more than the yield value and shear stress is proportional to the rate of shear strain is known as ideal plastic fluid.

Fluids applied today Petroleum Rapeseed oil, or canola oil Water-glycol Poly-glycol Oil-in-water Water Water-in-oil Synthetic fire-resistant fluids Vegetable oils

Types of Fluid Power System Based on Control system Open-loop Closed loop Based on Type of Control Fluid logic Control Electrical Control Electronic Control Based on Fluid Hydraulic Pneumatic

Fluid Power Symbols

Questions What are the primary functions of hydraulic fluid? Name few properties of a hydraulic fluid Mention Characterizes liquid and gas. What is density of fluid? What is meant by viscosity? What is the significant of viscosity, with reference to selection of fluids? What are the undesirable effects when oil having high viscosity? What are the undesirable effects when oil having very low viscosity? State the effects of temperature and pressure on viscosity of fluid. Define viscosity index What is meant by compressibility of fluid?

Function Properties Classifications Functions Vs Properties Hydraulic Fluid

Summary Primary functions It is a substance, capable of flowing. To transmit power To lubricate moving parts To seal clearances between parts and To cool or dissipate heat It is a substance, capable of flowing. Classified into liquid, gas vapor Liquids are assumed to be incompressible Gases are compressible Classified based Properties of fluid: Ideal fluid Real fluid Newtonian fluid Non-Newtonian fluid Ideal Plastic Fluid

MCQ   1. are shapeless substances that take the shape of their containers; they can be liquids or gasses. a) Air b) Water c) Oil d) Fluids   2. power is pressurized liquid or gas in a closed system. a) Fluid b) Electrical c) Mechanical d) Thermal 3. _____________________use pressurized oil or other liquids. a)Pneumatics b) hydraulics c) Electrical d) Electromechanical 4. use pressurized air or other gasses.  Pneumatics b) hydraulics c) Electrical d) Electromechanical 5. By itself, fluid has no power, but when confined and placed under , fluid can transmit power that can be stored, directed and made to do work. a) Volume b) Force c) pressure d) Area