Operation; Notion Of Internal And External Leakage - Etesia HYDRO 124D Technical Training Manual

Operation

The shaft (5) is coupled with a drive system (for example : an engine).
The pistons are fixed on the tilting plate by means of a ball joint and are driven in their
rotation by the cylinder barrel in which they are lodged.
The oil is distributed by the distribution plate (this plate is fixed).
The incline of the plate determines :
- The direction of circulation of the oil
- The volume of oil moved per turn ranging from 0 litre/minute (dead centre = no suction or
discharge because there is no movement of the piston in relation to the cylinder barrel) to
maximum flow (58 litres/minute).
On the Hydro124D, the piston pump is coupled with the crankshaft of the diesel engine, on
the flywheel side. The tilting plate is controlled by the drive pedals.

Notion of internal and external leakage.

All power units or hydraulic receivers have a normal degree of leakage which varies
according to the mechanical clearance, the pressure and the viscosity of the oil.
We can distinguish two types of leakage :
- Internal leakage : the oil from this type of leakage is directly reintroduced into the suction
system, except for the drive transmission pump drain which is connected directly to the tank.
- External leakage : the oil from this type of leakage is evacuated to the tank by a pipe or
drainage hose. Not to be confused with an oil sump leak.
As a result, the drive transmission pump is equipped with a booster pump whose role is to
compensate for the external leakage by reintroducing oil (taken from the tank) into the
(closed) circuit.
The oil from external leakage is filtered on its return to the tank which allows the depollution
of the closed circuit.
The fresh oil allows the heat exchange of the oil in the closed circuit (to avoid excessive
increases in temperature).
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