book in series
of 450 bar and peak pressures of 600 bar; rotational speed
ranges between 100 and 2000 rpm, overall efficiency
amounts to about 0.9, suction pressure is 0.9 absolute bar
and the recommended viscosity range is 15 ÷ 50 cSt.
More than one piston row can be assembled in a single
block in small and medium versions (Figure 4.55) so as to be
able to choose between a single high-flow outlet and more
outlets with different pressures and flows. Some companies
manufacture pumps equipped with up to six rows.
Figure 4.56
Axial piston pumps - Fixed displacement
Axial piston pumps are more popular than radial piston
pumps and have different designs that mainly fall into two
categories, depending on whether the cylinder block is in line
with he drive shaft or bent axis type.
Figure 4.54
It is important to specify if the cylinder block is rotary or fixed
in in-line piston pumps; piston reciprocation is made possible
by a round plate inclined vis-à-vis the axis of the transmission
shaft.
Swash plate pumps with fixed cylinder block are made up
of a swash plate solidly connected to the transmission shaft
(hence they revolve together) and a series of (ideally odd-
numbered) pistons in axial line with the same shaft and firmly
held in the pump casing. Suction and delivery valves ensure
that the fluid flows from the tank to the actuators.
Figure 4.55
Radial piston pumps - Variable displacement
Variable displacement radial piston pumps are similar to
rotary radial block pumps, but they differ in the reaction ring
that can move (Figure 4.56). Their adjustment and operating
principles are similar to variable displacement vane pumps:
stator ring shifting is affected by the delivery pressure versus
the force exerted by the spring of the hand wheel adjuster or
the compensator.
64 | JuNe-july 2018 | Global MDA Journal
Figure 4.57
The revolution of the swash plate makes pistons move
alternately; pistons are held by springs constantly connected
to the plate. The swash plate and the pistons can be connected
either via a ball joint/sliding block or directly, which means