3 液压与气压传动 英文版 福州大学 液压泵

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Hydraulic and pneumatic pressure transmission

Chapter 3 Hydraulic Pumps

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Chapter 3

Hydraulic Pumps

Chapter list3.1 Introduction 3.2 Piston Pumps 3.3 Vane Pumps 3.4 Gear Pumps

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Chapter 33.1 Introduction

Hydraulic Pumps

Hydraulic pumps convert mechanical energy into hydraulic energy. They supply fluid to the components in the hydraulic system.

3.1.1 Operating Principle

Fig. 3-1 Displacement pumps operation 1,2-Non-return valve; 3-Spring; 4-Cylinder 5-Piston; 6-Eccentric wheel

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Chapter 3

Hydraulic Pumps

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

s 2 e

V ( d / 4) s ( d / 2) e2 2

As described above, the basic conditions that constituted a hydraulic pump can be concluded as follows: (1) Oil tight chamber (2) Flow-deploying (separate the low pressure from the high one)4

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Chapter 3

Hydraulic Pumps

(3) The absolute oil pressure in the reservoir should be

equal or more than the atmospheric pressure3.1.2 Main performance parameters in hydraulic pumps 1. Pressure (1) Suction pressure —— the pressure in the inlet port. For self-primingsuction pumps, the suction pressure is lower than the atmospheric pressure. (2) Working pressure p ——the outlet pressure when the hydraulic pump is in operation, which depends upon the overall loads. (3) Rated pressure pS —— the highest pressure tested with standard method when the pump rotates continuously under common working conditions.

2. Delivery flow rate and volumetric efficiency(1) Delivery V5

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Chapter 3

Hydraulic Pumps

(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 qInstantaneous theoretical flow rate qshRated flow rate qs6

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Chapter 3

Hydraulic Pumps

3. Power and efficiency

(1) Input power pr (2) Output power P (3) Volumetric efficiency η

v

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Chapter 3

Hydraulic Pumpsm

(4) Mechanical efficiency η

(5) Overall efficiency η and mechanical efficiency η

m

4. Rotating speed(1) Rated rotating speed ns : the highest rotating speed for normal continuous and long- time operation under rated pressure. (2) Highest rotating speed nmax: the highest rotating speed for short-time operation under rated pressure, which may be higher than ns. (3) Lowest speed nmin: the lowest speed of the pump for normal operation. (4) Range of rotating speed : the speed range between nmin and nmax.8

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Chapter 33.1.3

Hydraulic Pumps

Performance curves

Fig.3-2 shows a performance curve of a hydraulic pump, in which the abscissa represents working pressure p of the hydraulic pump and the ordinate the volumetric efficiencyηv (or the practical flow rate q), overall efficienc

yη and input powerPr.

Fig. 3-2 Performance curves of hydraulic pumps 9

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Chapter 3

Hydraulic Pumps

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 curve ηv, and the equal power curve Pri.

Fig. 3-3 General performance curves of hydraulic pumps 10

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Chapter 33.1.4 Classification

Hydraulic Pumps

Hydraulic pumps may be classified by the forms of main moving components and their moving manners: gear, vane, piston and screw pumps. (1)Gear pumps may be further classified in two broad categories, external or internal mesh; (2)Vane pumps may be further divided into double-acting vane pumps, singleacting vane pumps and cam-rotor vane pumps; (3)Piston pumps consist of radial piston pumps and axial piston pumps; (4)Screw pumps include single-screw pumps, two-screw pumps and three-screw pumps. Hydraulic pumps may be further classified according to the types of delivery: 1) Fixed delivery; 2) Variable delivery: variable delivery can be accomplished in single-acting vane pumps, radial or axial piston pumps.

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Chapter 3

Hydraulic Pumps

3.1.5 Graphic symbolsThe graphic symbols of hydraulic pumps are shown in Fig.3-4.

Fig. 3-4 Graphic symbols12

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Chapter 3

Hydraulic Pumps

3.2 Piston PumpsThe oil suction and delivery actions of a piston pump depend upon the size change of the chamber produced by the reciprocating movement of the pistons wit …… 此处隐藏：4236字，全部文档内容请下载后查看。喜欢就下载吧 ……