BOOK IN SERIES
Some fundamental steps must be taken in order to install
the pump in the tank correctly. As many manufacturers
recommend, it is advisable to position it with the controller
placed upward (see Figure 4.48); motor pumps are usually
mounted below the fluid level in high-flow and high-pressure
systems. The drainpipe must not be connected to the output
hose, but directly to the tank, away from the inlet and below
the minimum level in order to prevent foam from forming.
Figure 4.48
Besides the measures on shaft alignment and antivibration
plugs that have already been described, other actions should
be taken, like adding an air bleed and, after the installation,
prefilling the pump via the drain hole (Figure 4.49).
Figure 4.46
When the stator ring is in the left position y, the pressure of
the system has exceeded the maximum level: the piston of a
specific cylinder is at the end of the stroke or the directional
valve is at an intermediate position with closed centres. In
theory the pressure is maximum, the flow rate is zero and
little power is absorbed, that is as much power as it is needed
to keep the rotor/vanes unit sliding and overcome internal
resistances. Actually, there is no flow in the user circuit, but
it continuously circulates throughout the pump. The fluid
leaked through the sliding parts flows back into the tank via
a drainpipe, thus ensuring the heat exchange needed and an
excellent lubrication.
Installation of a variable displacement vane pump
Figure 4.49
The typical stationary application of variable displacement
pumps is on machine tools that require pressures of about 120
– 130 bar (hydraulic compensator), 70 – 80 bar (mechanical
controller) or, in many cases, much lower pressures.
Figure 4.47
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Global MDA Journal may 2018