Nowadays,
each hydraulic pump found in almost any industrial and mobile
application uses pistons, vanes or gears to create a pumping action
that produces constant flow. Each method of pumping action of a
hydraulic pump features individual characteristics that differ
it from all the others and make it suitable for a particular range of
application.
Piston
Pumps
The
pumps with the highest input speed capabilities are the piston pumps.
They usually have pistons arranged in a radial or axial fashion. The
radial types are used only when applications require very high power,
while the axial types are used in a wide range of pressure
capabilities and displacement (which makes them very suitable for
various mobile and industrial tasks). The axial-piston pumps consist
of a set of pistons fitted in a cylinder block and powered by an
angled swash plate. As the swash plate rotates, the pistons provide a
pumping action so that reciprocate bores in the cylinder block. A
unique characteristic of the piston pumps is that the displacement
can vary with changing the angle of the swash plate.
Piston
pumps have a greater service life than any other hydraulic pump,
but also highest pressure ratings and a significant advantage of
variable displacement, which makes them the best choice for
application where high power and high efficiency are important.
Vane
Pumps
Vane
pumps are know for making very little vibration and being the
quietest pumps. They generate flow using a set of vanes which can
move along within a slotted rotor that rotates in an elliptical
chamber. A typical vane pump uses an elliptical cam ring with a rotor
spinning in the cylinder and a pair of side plates to form the
pumping chambers. The displacement is possible to vary, but it is not
a common occasion. Most vane pumps used in mobile and industrial
applications have a fixed and stable displacement.
Vane
pumps are hydraulically balanced, which means their efficiency is
enhanced a lot. Many designs of this kind of hydraulic pump, I
mean vane pump, place the rotating group in cartridge, so their
repair is much easier. The whole rotating group can be easily removed
and replaced by removing the back cover, pulling out the damaged
rotating cartridge and replacing it with a new one.
Gear
Pumps
Gear
pumps are known for having the shortest service life, so they are
much more often replaced than repaired because
of the cost. The gear pumps are very simple and they use a pair of
gears which rotate in an oval chamber to produce
a constant flow. With the gear rotating, the size of the chambers
changes and so provides the pumping action. There are other designs
that use an external rotating ring with internal gear teeth that mesh
an internal gear as it rotates. As the internal gear rotates, the
tooth engagement creates chambers of diminishing size between the
inlet and outlet positions to create flow.
More
sophisticated variants of gear pumps is the gerotor pumps, consisted
of a non-concentric internal and external rotor with different
numbers of teeth. As the internal and external rotor rotate, the
pumping action is created by the changing volume of the space between
the rotors.
All
gear pumps have a fixed displacement, making them relatively
inexpensive compared to the piston and vane pumps with similar
displacements. Unfortunately, as mentioned above, they have a shorter
service life than any hydraulic
pump
and are not generally economically repairable.
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