Successfully completing this lesson
you'll be familiar with the operation of
reciprocating pumps single and double
acting reciprocating pumps the operation
of several different rotary
positive-displacement pumps the relief
valve in positive-displacement pumps the
lesson will end with a test
positive-displacement pumps have one of
two basic designs either reciprocating
or rotary it's time for a quick quiz as
we've seen positive-displacement pumps
have two basic designs rotary and
reciprocating which of these two pumps
is a rotary pump click on the correct
illustration if you're not sure
go to the previous screen to refresh
your memory correct the pump to the
right is a rotary pump
positive-displacement pumps differ from
centrifugal pumps in that they use
mechanical energy to transfer fluid if
the displacement is on the forward
stroke only then the pump is
single-acting this pump is double acting
because it displaces liquid both on the
forward and return stroke
it's time for a quick quiz is this pump
a single acting or a double-acting pump
if you're not sure
go to the previous screen to refresh
your memory correct
the pump is a double-acting pup since it
displaces liquid on both the forward
stroke and the return stroke
here's an illustration of a
reciprocating pump system
positive-displacement pumps are capable
of delivering very high pressures these
pressures can be much an excess of the
design pressure and so a relief valve
must protect the pump
positive-displacement pumps are self
priming as the section and delivery are
positively separated
pumping
however in order to reduce wear and
ensure quick starting an external
priming connection from above the pump
should be available reciprocating pumps
can produce pressure fluctuations in the
discharge pipelines a damper either gas
or air filled can help to even out the
pressure fluctuations the damper stores
some of the energy as the pressure rises
and releases this energy as the pressure
Falls it's time for a quick quiz drag
the relief valve to its corresponding
pipe if you're not sure
go to the previous screen to refresh
your memory correct most
positive-displacement pumps and use our
of the rotary type rotary pumps operate
in a circular motion and displace a
constant amount of liquid with each
revolution of the pump shaft
this is accomplished by the pumping
elements moving in such a way as to
expand volumes to allow liquid to enter
the pump these volumes are contained by
the pump until the geometry causes the
elements to move to reduce the volume
and force the liquid out the clearances
of the elements within the pump separate
the suction from the discharge and are
critical for efficient operation rotary
piston type positive-displacement pumps
are found in hydraulic systems there are
two types radial piston and axial piston
you can see that the Pistons rotate
eccentrically to the rotor axis this
causes the cylinder volume to increase
as the Pistons past the suction port and
decrease as the Pistons past the
delivery port in some applications such
as steering gear applications the pump
can have a variable discharge this is
achieved by increasing and decreasing
the eccentricity of the Pistons thereby
change
the amount of cylinder volume increase
the nature of the ports can also change
by moving the piston eccentricity past
the pump centerline an axial piston pump
is sometimes known as a swash plate pump
the principle is the same as for the
radio type an axial piston pump can also
be used as a variable delivery pop gear
pumps rely on the meshing of gear wheels
to separate the suction and delivery
ports they come in two configurations
either internal gear or external gear
internal gear pumps use the same
principle as the external type in this
case the driven gear has internal teeth
and meshes with the idler which has
external teeth the external gear pump
has two gearwheels one driven by the
motor and the second or idler which is
driven by the meshing of the gears the
gears carry the liquid around the
outside and the meshing of the teeth
cause the liquid to be discharged it's
time for a quick quiz as we've seen gear
pumps come in two configurations
internal gear and external gear which of
these two pumps is an external gear pump
click on the correct illustration if
you're not sure
go to the previous screen to refresh
your memory correct the pump to the left
is an external gear pump screw-type
pumps usually have either two or three
screws they can operate at high speeds
and give a smooth discharged with almost
no pulsations they come in two
configurations either twin screw pump or
three scoop up the twin screw pump uses
a similar principle to the gear pump in
that the liquid is carried between the
screw and the casing the meshing of the
screws
also the liquid to be discharged due to
the imbalance of forces this type of
pump often has the suction arranged at
the center of the screws and the
delivery at either end and is often
driven through timing gears which keep
the screws from contacting each other 23
screw pump is usually arranged so that
the central screwdrivers the two outer
screws a special type of screw pump is
the single screw or progressive cavity
pump this pup has a single-screw
rotating in stator the stator is made of
an elastomeric material the stator has
an internal helix of different pitch to
the rotor the geometry means that the
rotor moves vertically whilst turning so
the meshing of the rotor and stator
causes the cavity to progress to the
discharge the screw is an interference
fit in the stator so this pump must
always have liquid present to prevent
overheating and failure
it's time for a quick quiz which part of
a progressive cavity pump is called a
stator click on the stator if you're not
sure
go to the previous screen to refresh
your memory correct vane pumps come in
two configurations either flexible vane
pump or sliding vane pump the rotor is
made of an elastomer and as the veins
past the cam they deflect decreasing the
cavity and so discharging the liquid the
veins are a sliding fit in slots cut in
the rotor the rotor turns eccentric to
the casing causing the cavities to
decrease in volume veins can be four
stop by centrifugal force use springs or
utilize the pressure of the discharge
liquid it's time for a quick quiz where
are the veins located
click on the veins if you're not sure
go to
the previous screen to refresh your
memory correct