successfully completing this lesson
you'll be familiar with series pumping
multistage parallel pumping the lesson
will end with series pumping can be
considered as a series of centrifugal
pumps arranged to supply one another in
series and thus progressively increase
the discharge pressure the illustration
shows a cross-section through a typical
vertical multi-stage single-entry
centrifugal pump used for deep well
cargo pumping the pump drive is located
outside the tank and can be electric or
hydraulic here a diffuser is fit to
assist and raising the discharge
pressure it is a ring fixed to the
casing around the impeller in which
there are passages formed by veins the
passages widen out in the direction of
the liquid flow and act to convert the
kinetic energy of the liquid into
pressure energy in the same manner as a
valued casing hydraulic balance
arrangements are also customary some of
the high pressure discharge liquid is
directed against a drum or piston
arrangement to balance the discharge
liquid pressure on the impeller and thus
maintain it in an equilibrium position
in serious operation the discharge of
one pump feeds the suction of a second
pump when two or more pumps are operated
in series the flow through all of the
pumps is equal since whatever flows
through one pump has to flow through the
next pump in series provided there are
no side streams
let's take a closer look at pump curves
for the purposes of this lesson you must
create a pump curve chart for identical
pumps used in series
let's start by adding ahead to flow
curve for one pump to the chart drag the
pump icon onto the pipeline click the ad
curve button
let's add a combined head to flow curve
for two identical pumps drag the second
pump icon onto the pipeline click the ad
curve button
let's add a combined head to flow curve
for three identical pumps drag the third
pump icon onto the pipeline click the ad
curve button if pumps are used in series
in a system a combined pump curve can be
generated analogous to the combined
curve though the combined curve is
generated differently of course again
the same general rule applies namely
that the intersection of the combined
pump curve with the system head curve
determines the total flow delivered to
the system and allows one to determine
where on its own head to flow curve each
of the pumps is running
for the purposes of this lesson you must
create a pump curve chart for identical
pumps used in a system with a steep
system head curve
let's start by adding ahead to flow
curve for one pump to the chart drag the
pump icon onto the pipeline click the ad
curve button
let's add ahead to flow curve for two
identical pumps in parallel drag the
pump icon onto one of the pipeline's
drag the second pump icon onto the other
pipeline click the ad curve button
let's add the head to flow curve for
three identical pumps in parallel drag
the pump icon onto one of the pipeline's
drag the second pump icon onto one of
the remaining pipelines drag the third
part by con onto the last pipeline click
the ad curve button
let's add the head to flow curve for two
pumps and series drag the pump icon onto
the pipeline
drag the second pump icon onto the
pipeline click the ad curve button
this illustration shows that when the
system head curve is very steep
operating a second pump in parallel with
the first produces only a marginal
increase in flow if these same pumps
were piped in series rather than in
parallel they would produce a higher
flow through the system the illustration
shows that only two such pumps piped in
series deliver more flow through the
system than three pumps operating in
parallel do so the general rule is that
if the system head curve is relatively
steep series pumping is probably more
effective than parallel pumping for
increasing the flow range of the pumps
the opposite is also true we're fairly
flat system head curves are concerned
parallel company is probably more
effective producing wide flow range than
series pumping is and finally you must
create a pump curve chart for
non-identical pumps used in series
let's start by adding ahead to flow
curve for one pump to the chart drag the
pump icon onto the pipeline click the ad
curve button
drag the second pump icon onto the
pipeline click the ad curve button click
the ad curve button
the illustration shows the combined pump
curve for two non-identical pumps
operating in series the combined curve
is generated using the same procedure as
for identically sized pumps at the
arbitrarily selected flow rates the
total delivered head of the two pumps
are added together to produce the
combined curve data point it is common
in pipelines to have several differently
sized pumps allowing the operators the
widest possible range of flow and or
variation of products pumped
the specific speed of a centrifugal pump
is the revolutions per minute at which a
geometrically similar pump would run in
order to deliver one cubic meter per
hour against one meter head it's derived
by the following formula
the primary purpose of operating pumps
in parallel is to allow a wider range of
flow than would be possible with a
single fixed speed pump for systems with
widely varying flow demand examples of
applications for parallel pumping
include municipal water supply and waste
water pumps pumps and water chilled
heating ventilating and air-conditioning
systems main process pumps and a
variable capacity process plant and
condensate pumps in a steam power plant
usually there are no more than three or
four pumps operating in parallel when
parallel pumps are being considered for
a system design the pumps must be
carefully matched to each other and to
the system to ensure that the pumps are
always operating at a healthy point on
their head to flow curves and to ensure
that the system is such that true
benefits are achieved from the parallel
pumping arrangement
however this does not always turn out to
be the case
in order to analyse a parallel pumping
arrangement it is necessary to construct
the system head curve then a combined
pump curve must be developed depicting
the head flow relationship for the pumps
while pumping in parallel
once these two curves are constructed
the rule for total system flow is that
the total flow through the system is
represented by the intersection of the
system head curve with the combined pump
curve the illustrations show the
combined pump curve is developed with a
system having either two or three
identical pumps operating in parallel
if the system head curve is too steep a
situation which could be caused by an
undersized piping system or by some
other under sized component in the
system which acts as a bottleneck then
it turns out that very little benefit is
achieved by operating pumps in parallel
in that system the situation the two
non-identical pumps operating in
parallel is shown in the diagram the
curves of the two different pumps are
combined and curve C by adding the flow
of the two pumps and arbitrarily
selected values of head the combined
curve is not a smooth one due to the way
it is generated as the graphical some of
curves a and B the combined curve C
actually follows curve a for a while
since the maximum head for Kirby is
lower than the maximum head for curve a
the same rule applies as before the
illustration shows that operating two
non-identical pumps and parallel can
present problems when the two
non-identical pumps are mismatched for
the system in which they're working the
system curve labeled curve Y is steeper
than the one shown before an attempt to
run these two pumps in parallel in the
system represented by system head curve
why would mean that the pump represented
by curve a would operate at the
intersection point of the combined curve
and the system head curve labeled point
a which is the same point it would
operate at when pumping alone in the
system