液压与气压传动（英汉双语）第2版教学课件作者陈淑梅第2章Chapter_2课件.pptVIP

（2）For the case of eccentric with inverse order conical annular clearance (Fig.2-30b) ：the side Force F will be created and it will reduce the eccentric value “e” (Fig.2-30b) to make the spool core centered in the seat. In fact, the hydraulic lock is objective and what we can do is to try to eliminate it. The most simple method is balance notches on the spool core. 2.6.1 Hydraulic shock 2.6.2 Cavitation 2.6 Hydraulic Shock and Cavitation 2.6.1 Hydraulic Shock Hydraulic shock and damages The types of hydraulic shock (1)That occurs due to the sudden reduction of the across-section of the orifice or change of the flow direction; (2)That results from the inertia of the high speed working components suddenly braking or changing direction. 1）Hydraulic shock results from fluid flow stopping suddenly Fig.2-31 Hydraulic impact (2-70) The fluid flow is stopped suddenly when the check valve is closed suddenly. According to conservation of energy, So Spread speed of shock wave in pipe can be calculated by (2-71) Formula (2-72) is initituled the whole hydraulic shock situation. The pressure peak value at non-whole hydraulic shock is less than the whole hydraulic shock and it can be calculated by (2-73) Formula (2-70) is only used to the closed pipe, i.e., the time t of the check valve closed is less than the time (time of critical close). (2-72) 2) Hydraulic shock resultes from the motion parts braked according to the conservation of momentum, the system shock pressure can be calculated: Example 2-7. If the inner diameter of pipe is d=200mm, the wall thickness 10mm, the initialization speed , pressure , the bulk modulus of elasticity of fluid MPa, the modulus of elasticity of pipe material MPa. Calculate the maximum pressure drop when the check valve is closed suddenly. Measures to reduce the hydraulic shock 1