Variable Displacement Pump - Dynamic Description (A.10.A.20.02 - C.30.A.10) - New Holland CX720 Repair Manual

DISTRIBUTION SYSTEMS - PRIMARY HYDRAULIC POWER SYSTEM
Hydraulic pump Variable displacement pump - Dynamic description
(A.10.A.20.02 - C.30.A.10)
1 Pump End Plate
3 Swash Plate
5 Drive shaft Gear
7 Slipper (9 off)
9 Inlet Port
11 Outlet Port
Principal of Operation
The operating principal of the fixed displacement gear pump is to provide a constant oil flow directly related to the
rotation speed of the pump.
The operating principal of a variable displacement piston pump is to provide oil flow on demand and minimises the
engine power absorbed in driving the hydraulic pump when the hydraulic circuits do not require maximum pump flow.
The variable displacement piston pump in hydraulic systems therefore has distinct power loss advantages over fixed
displacement gear type pumps, which continually provide oil flow and absorb engine power even when the hydraulic
circuits do not require the total pump output.
The feed oil for the variable displacement piston pump is called the charge oil. The charge oil is supplied by the return
flow of the hydrostatic drive system. This supplies 60 l/min (16 gal/min) of oil via the oil cooler. Only under high
demand situations, 60 - 114 l/min (16 - 30 gal/min), does an under pressure develop in the charge supply line.
Variable Displacement Piston Pump
The major components of the variable flow piston pump with closed centre load sensing are:-
1. A nine element pumping head.
2. A plate mechanism (swash plate) to adjust piston stroke and corresponding pump output.
Variable Displacement Piston Pump-Sectional Drawing
1
TIA35042
2 Swash Plate Servo Piston
4 Swash Plate Return Spring
6 Drive shaft
8 Piston and Barrel
10 Pumping Head Pre-load Spring
2 4/7/2006
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