BOOK IN SERIES
phenomenon in intravane pumps is quite mitigated because
the vane in the delivery area is fully subjected to the working
pressure while tightness during suction is guaranteed by the
pressurised fluid found only in the cavity. Balanced vane pumps are widely employed in self-propelled
machines, especially in the double version equipped with one
inlet and two outlets with different flow rates (for instance,
earthmoving equipment).
The operating principle of intravanes is similar to pin vanes.
The pressurised fluid is sent to the base of the vane via
two channels on the vane itself; the thrust pin pressure
is constantly ensuredby a channelinside the rotor and
connected to the bush (Figure 4.39). More sophisticated versions with double hollow vane have
the advantages of the pin thrust as well as the excellent
tightness of the two vanes (Figure 4.41).
Like intravanes, the vane is not subjected to delivery pressure
during suction and the pin makes it adhere to the stator. The
lack of splines feeding the cavity and radial holes on the rotor
that are typical in intravanes ensure more sturdiness to the
hollow vane pump.
The most advanced versions of balanced vane pumps can be
operated at maximum working pressures of 250 – 280 bar
and sustain 1800 revolutions – 200 bar at 300 l/min, speed
between 600 and 3000 rpm, overall efficiency of 0.85 and
absolute suction pressure of 0.85 bar. The recommended
oil viscosity ranges from 15 to 54 cSt under normal working
conditions.
These particular types of hydraulic generators can also be
started at a temperature well below zero. As a matter of fact,
the pump can be started with a fluid viscosity of 800 cSt, with
appropriate precautions recommended by manufacturers,
like initial low speed. Obviously, under these conditions the
whole system is operational when it warms up.
Figure 4.39
Figure 4.40
Figure 4.42
Variable displacement vane pumps
Figure 4.41
66
Global MDA Journal may 2018
Variable displacement vane pumps are based on the same
operating principle as fixed displacement pumps and they are
the type of pumps whose flow rate best adapts to the system
requirements. The balancing systems previously described
can be applied to variable displacement pumps only to a
limited extent, therefore efficiency and working pressures
drop dramatically. Virtually, these pumps are similar to the
obsolete fixed round pumps, but they differ in the obliquely
moving stator.