Review and Summary

REVIEW AND SUMMARY

• A hydraulic pump is a device which converts mechanical energy into hydraulic energy.

• Pump classification:

1. Non positive displacement (hydro-dynamic) pumps, and

(a) Centrifugal pumps, (b) Axial flow pumps, and (c) Mixed flow pumps.

2. Positive-displacement (hydro-static) pumps, and

(i) Rotary pumps

(a) Gear pumps, (b) Vane pumps, and (c) Screw pumps.

(ii) Reciprocating pumps

(a) In-line axial piston pump,

(b) Bent axis axial piston pump, and

(c) Radial piston pump.

• The non-positive displacement (i.e., centrifugal) pumps are used only for transporting fluid from one location to another location. They are not preferred in the fluid power industries because these pumps cannot withstand high pressures. 

• The positive displacement pumps discharge fixed quantity of fluid into the hydraulic system per revolution of pump shaft rotation. These pumps are widely used in all fluid power applications.

• The construction and operation of different types of pumps such as external gear pump, internal gear pump, lobe pump, gerotor pump, screw pump, unbalanced and balanced vane pumps, and axial and radial piston pumps have been discussed in this chapter.

• Formulae Summary :

1. Theoretical discharge : QT (m3/min) = VD (m3/rev) × N (rpm)

2. Volumetric efficiency:

3. Gear pump volumetric displacement:

4. Vane pump volumetric displacement:

5. Piston pump volumetric displacement: VD = Y A D tan θ

6. Piston pump theoretical flow rate: QT = Y A D tan θ 

7. Radial piston pump theoretical flow rate: QT =  0.5 е Y лd2 N

10. Pump overall efficiency:

• At the end of the chapter, various pump characteristics and about selection of pumps are presented.

KEY TERMS ONE SHOULD REMEMBER

Pump

Positive displacement pumps 

Hydrostatic displacement

pumps

Fixed displacement pumps 

Variable displacement pumps 

Non-positive displacement

pumps

Hydrodynamic displacement pumps 

Gear pumps

External gear pumps

Internal gear pumps

Lobe pumps

Gerotor pumps

Vane pumps

Unbalanced vane pumps 

Balanced vane pumps

Piston pumps

Axial piston pumps 

Bent axis type 

Swash plate type 

Radial piston pumps 

Volumetric displacement 

Theoretical flow rate 

Volumetric efficiency

Mechanical efficiency

Overall efficiency 

Brake power 

Hydraulic power

Pump characteristics

 Characteristics curves 

Pump performance 

Pump noise 

Slip

Cavitation

Pump ripple 

Pump selection

Screw pumps