液压与气压传动（英汉双语）第2版教学课件作者陈淑梅第3章Chapter_3课件.pptVIP

Chapter 3 Hydraulic Pumps Chapter list 3.1 Introduction 3.2 Piston Pumps 3.3 Vane Pumps 3.4 Gear Pumps 3.1 Introduction 3.1.1 Operating Principle 3.1.2 Main performance parameters in hydraulic pumps 3.1.3 Performance curves 3.1.4 Classification 3.1.5 Graphic symbols 3.1.1 Operating principle The operating principle of every pump in a hydraulic system depends upon the alternative change of their working volumes. Note: the piston diameter as d, the offset of the eccentric wheel as e, the longest stroke the piston can reach as s and the discharged oil volume V, then As described above, the basic conditions that constitute a hydraulic pump can be concluded as follows: 1) Oil tight chamber. 2) Flow-deploying (separate the low pressure from the high one). 3) The absolute oil pressure in the reservoir should be equal or more than the atmospheric pressure. （2）Flow rate The flow rate consists of the average theoretical flow rate, the practical flow rate and the instantaneous theoretical flow rate. Average theoretical flow rate qt Practical flow rate q Instantaneous theoretical flow rate qsh Rated flow rate qs 3. Power and efficiency (1) Input power pr (2) Output power P (3) Volumetric efficiency ηv (4) Mechanical efficiency ηm (5) Overall efficiency η and mechanical efficiency ηm 3.1.3 Performance curves For some hydraulic pumps with certain rotating speed ranges or variable displacement capacity, the format of the general characteristic curves shown in Fig. 3-3 are commonly used to reflect all their performances. The abscissa represents the working pressure p of the pump and the ordinate represents the pump’s flow rate q, rotating speed n or delivery V. Fig. 3-3 also shows the equal efficiency curveηv, and the equal power curve Ｐri. 3.1.4 Classification 3.1.5 Graphi