Hydraulic and pneumatic pressure transmissionChapter 2 Fundamental Hydraulic Chapter 2 Fundamental Hydraulic Fluid Mechanics Fluid MechanicsChapter 2 Fundamental Hydraulic Fluid Mechanics 22.1 Performances of the Hydraulic Oil 2.2 Hydrostatics 2.3 Hydrodynamics 2.4 Characteristics of Fluid Flow in Pipeline2.5 Flow Rate and Pressure Features of Orifice 2.6 Hydraulic Shock and Cavitation Chapter 2 Fundamental Hydraulic Fluid Mechanics 32.1.1 The main performances 2.1.2 The requests and choice of hydraulic oil 2.1 2.1 Performances of the Hydraulic Oil Chapter 2 Fundamental Hydraulic Fluid Mechanics 41. Density (Kg/m3) 2. Compressibility 2.1.1 The main performances the coefficient of compressibility , K is the bulk modulus of elasticity（2-2）（2-1）K is defined as the ratio of the change in pressure ( ) to relative change in volume ( ) while the temperature remains constant. Chapter 2 Fundamental Hydraulic Fluid Mechanics 53. Viscosity The experiments have proved that friction force between the two fluid molecules can be described asWhere is viscosity coefficient, also dynamic viscosity. Fig.2-1 The sketch of viscosity The sketch of viscosity is illustrated by Fig. 2-1. （2-3）Cohesion between two moleculesChapter 2 Fundamental Hydraulic Fluid Mechanics 6There are three methods to describe the viscosity: absolute viscosity, Kinematic viscosity and relative viscosity.(1) Dynamic viscosity or absolute viscosity(1) Dynamic viscosity or absolute viscosity (Pas) or (N s/m2) (2) Kinematic viscosity (mm(2) Kinematic viscosity (mm2 2/s)/s) （2-4）(3)(3) Relative viscosity (conditionalRelative viscosity (conditional viscosity) The relative viscosity 0E which used in China is tested by the 0E viscometer, such as Fig.2-2.Chapter 2 Fundamental Hydraulic Fluid Mechanics 7Fig.2-2 Principle of 0E viscometer Fig. 2-2 illustrates the 0E viscometer principle.Chapter 2 Fundamental Hydraulic Fluid Mechanics 8Take the note 0Et describes the viscosity:The conversion formula between the 0E and kinematic viscosity is: (m2/s)(4) Viscosity-temperature(4) Viscosity-temperature : For the viscosity less than 15 0E and the temperature 300C150 0C, the viscosity-temperature formula is describe as following: We also can look up from Fig.2-3.（2-5）（2-6）（2-7）(5) (5) Viscosity-pressure （2-8）(6) Others performances(6) Others performances : physical and chemical, such as anti-inflammability, anti- oxygenation, anti- concreting, anti-foam and anti-corrosion etc Chapter 2 Fundamental Hydraulic Fluid Mechanics 9Fig. 2-3 The viscosity-temperature of homemade oils Chapter 2 Fundamental Hydraulic Fluid Mechanics 10n RequestThe oil plays two roles of transmission energy and lubrication on the surfaces of working interaction.The requests for the hydraulic fluids are: appropriate viscosity, the good in property of favorable viscositytemperature, a good lubricity, chemically and environmentally stabilities, compatible with other system materials and so on. 2.1.2 The requests and choice of hydraulic oil2. Choice The hydraulic oil in a hydraulic system at is recommended generally.The hydraulic oil should be chosen in according to the request of hydraulic pump. The hydraulic oil viscosity adapted for different hydraulic pumps is listed in Tab. 2-2.Chapter 2 Fundamental Hydraulic Fluid Mechanics 11Tab. 2-2 The range of viscosity of hydraulic oil adapted to pumps Typesviscosities (10-6 m2/s)TypesViscosities(10-6 m2/s)5 4040 805 4040 80 Vane PumpsPCr，neglect Cr ,the flow rate asThe flow rate coefficient can be obtained by Fig. 2-22, the Reynolds number can be calculated by following, (2-44)(2-45)(2-46)Chapter 2 Fundamental Hydraulic Fluid Mechanics 49For a hydraulic valve whatever flowing in or out, is the angle between streamline and spool line and is called speed direction angle,it is usually .Fig. 2-22 Flow coefficient on the orifice of spool valve Chapter 2 Fundamental Hydraulic Fluid Mechanics 50The poppet valve orifice is shown in Fig. 2-23,When poppet moves up a distance of , the average diameter of , , then the flow rate is Fig. 2-23 Orifice shape of poppet valveFig.2-24 Flow coefficient of poppet valve orifice(2-47)where the flow rate coefficient can be obtained by Fig. 2-24Chapter 2 Fundamental Hydraulic Fluid Mechanics 512.5.2 Stubby orifice or slot orifice Fig. 2-25 flow rate coefficients in Stubby orificeThe flow rate equation for slot orifice obeys the formula (2-31),i.e. The flow rate equation for the stubby orifice is the same as formula (2-42), but the flow rate coefficient can be obtained from the curve in Fig. 2-25. The stubby orifice is defined as ：