book in series
The main displacement adjustment diagrams, which are
usually applied to axial piston pumps, are shown below (see
next chapter for an in-depth analysis of each compensator
and their problems).
The two cylinders are the internal elements for the
adjustment of the plate or the moving cylinder block: the
cylinder provided with a spring is the opposing piston, that
keeps the pump in maximum displacement, while the other is
the inclination piston. The valves connected to the inclination
cylinder represents the operating type of the real controller,
directly assembled outside the pump casing.
Figure 4.68
Also variable displacement pumps with rotary cylinder block
in line with the drive shaft have very few differences in
respect to the fixed type, like the mechanism that performs
the inclination of the plate (Figure 4.69).
They are quicker than bent axis versions in the transients
because the disk has less inertia than the cylinder block, they
are cheaper to manufacture and can be mounted in tandem.
The pressure compensator or controller keeps the delivery
pressure constant, albeit with flow variations. Pump output
(standby) is carried out by adding a monostable solenoid
valve 3/2 to the controller. In the NC version (normally closed
solenoid valve), the solenoid excitation operates the standby;
the NO (normally open solenoid valve) is excited during the
operational phases and immediately starts the pump output
then the voltage supply switches off (Figure 4.71).
Figure 4.71
Figure 4.70
Displacement adjustment circuits
Except for manual control setting, displacement variation is
performed by automatic controllers, which adjust pressure or
flow, or all the parameters altogether, which keep power constant.
68 | JuNe-july 2018 | Global MDA Journal
Figure 4.72