Chapter 6 Auxiliary Components for Hydraulic Systems It includes two processes:filled in oil fluid (accumulation)and discharging out oil fluid(release). 1.Filled in oil fluid(accumulation) It is an equilibrium state of pressure difference on the two sides of upper and down on the interlayer with the operating oil volume as V1 after displacement out oil fluid (release)shown in Fig.6-2a. When operating oil pressure in the accumulator is increased with the oil pressure in hydraulic system,the interlayer losses equilibrium and moves up under the action of operating difference,as shown in Fig.6-2b. Homepage List Upwards Downwards Retumn Exit
Chapter 6 Auxiliary Components for Hydraulic Systems 6 1. Filled in oil fluid (accumulation) It is an equilibrium state of pressure difference on the two sides of upper and down on the interlayer with the operating oil volume as V1 after displacement out oil fluid (release) shown in Fig. 6-2a. When operating oil pressure in the accumulator is increased with the oil pressure in hydraulic system,the interlayer losses equilibrium and moves up under the action of operating difference, as shown in Fig. 6-2b. It includes two processes: filled in oil fluid (accumulation) and discharging out oil fluid (release)
Chapter 6 Auxiliary Components for Hydraulic Systems 2.Discharging out oil fluid(release) When the system pressure is lower than the pressure of the operating oil,the interlay is moved down under the action of gas pressure(or weight loaded or spring loaded);at the same time oil is discharged out of the accumulator and flows into the system until a new pressure equilibrium on the two sides of the interlayer as shown in Fig.6-2c. 6.1.2 Applications Such an accumulator can be used to advantage in a number of hydraulic applications: 1)To supply oil lost through leakage in a system held under pressure but not operating for long periods.To serve as an auxiliary or emergency source of hydraulic power where pump Homepage List Upwards Downward达 Return Exit
Chapter 6 Auxiliary Components for Hydraulic Systems 7 2. Discharging out oil fluid (release) When the system pressure is lower than the pressure of the operating oil, the interlay is moved down under the action of gas pressure (or weight loaded or spring loaded); at the same time oil is discharged out of the accumulator and flows into the system until a new pressure equilibrium on the two sides of the interlayer as shown in Fig. 6-2c. 6.1.2 Applications Such an accumulator can be used to advantage in a number of hydraulic applications: 1) To supply oil lost through leakage in a system held under pressure but not operating for long periods. To serve as an auxiliary or emergency source of hydraulic power where pump
Chapter 6 Auxiliary Components for Hydraulic Systems or feed line have failed.To operate a secondary circuit intermittently in connection with a constant duty primary circuit without affecting the speed or loading of the primary circuit. To compensate for expanding and contracting volumes due to thermal changes. 2)To supply holding pressure where the operating cycle calls for pressure to be applied for a long periods of time.For example, an accumulator can be used to avoid accident when the pump fails randomicity at starting. 3)To absorb pulsations,surges,or shocks from reciprocating pumps or quick closing valves.To cushion and lower the noise the load on fork lifts,front end loaders,backhoes,etc 8 Homepage List Upwards Downwards Return Exit
Chapter 6 Auxiliary Components for Hydraulic Systems 8 or feed line have failed. To operate a secondary circuit intermittently in connection with a constant duty primary circuit without affecting the speed or loading of the primary circuit. To compensate for expanding and contracting volumes due to thermal changes. 2) To supply holding pressure where the operating cycle calls for pressure to be applied for a long periods of time. For example, an accumulator can be used to avoid accident when the pump fails randomicity at starting. 3) To absorb pulsations, surges, or shocks from reciprocating pumps or quick closing valves. To cushion and lower the noise the load on fork lifts, front end loaders, backhoes, etc
Chapter 6 Auxiliary Components for Hydraulic Systems 6.1.3 Calculation of parameters 1.Calculation for the charged gas volume o The volume of an accumulator is the charged gas volume for a bag accumulator p%”=p”=p2V” -Constant (6-1) (1)For the isothermal changes The involvement no change in temperature,and no internal energy changes occur in the gas.Take n=1,then △V 6-2) p.( Homepage List Upwards Dowrwards Return Exit
Chapter 6 Auxiliary Components for Hydraulic Systems 9 6.1.3 Calculation of parameters 1. Calculation for the charged gas volume V0 The volume of an accumulator is the charged gas volume for a bag accumulator 0 0 1 1 2 2 n n n p V p V p V = = ＝Constant （6-1） (1) For the isothermal changes The involvement no change in temperature, and no internal energy changes occur in the gas. Take n=1, then 0 0 1 2 ( ) 1 1 V V p p p = − （6-2）
r 6 Auxiliary Components for Hydraulic Sys (2)For the adiabatic(isentropic)changes The other bounding condition is a reversible adiabatic (isentropic)change which takes place so rapidly that no flow of heat into or out of the gas occurs.The defining relationship is △V Vo三1 -(写 1 (6-3) p (3)For polytropic changes Practically accumulator gas can follow any number of polytropic changed,which is isothermal during accumulating and adiabatic during discharging due to gas expanded.It can be so calculated by 10 Homepage List Upwards Downwards Return Exit
Chapter 6 Auxiliary Components for Hydraulic Systems 10 0 0 1 1 1 1 2 1 1 [( ) ( ) ] n n n V V p p p = − (2)For the adiabatic(isentropic)changes The other bounding condition is a reversible adiabatic (isentropic) change which takes place so rapidly that no flow of heat into or out of the gas occurs. The defining relationship is (3) For polytropic changes Practically accumulator gas can follow any number of polytropic changed, which is isothermal during accumulating and adiabatic during discharging due to gas expanded. It can be so calculated by （6-3）