Improving Pump Performance To Increase
Profitability of Retail Fuel Sales
A White Paper
Veeder-Root Company
125 Powder Forest Drive
Simsbury , CT 06070
USA
Telephone: 860-651-2700
Fax : 860-651-2719
www.veeder.com
October 2004
This is the distance from the product in
P
ump performance plays critical role
in delivering high profitability in the tank to the point of discharge into a
retail gasoline sales. The right car tank or loading rack. In a
pump can maintain flow rates at high lev- submersible pumping system the pump
els during peak periods in order to move must be able to perform under the worst
customers through the station quickly case scenario of a near empty tank. In
and avoid frustration, which could cause bottom loading applications, the highest
them to cut purchases short. Just as point in the tanker is taken as the point
important, pumps that deliver consistent, of discharge. The static head can vary
reliable performance will help to prevent with the tank level, typically resulting in
shutdowns that could cost thousands of a difference of 7 to 11 feet or about 2 to 3
dollars in revenue per hour at a high vol- psi in the pressure of the pump. It’s
ume site. Pumping performance also important to note that the effect of the
affects profitability in subtler ways, such static head does not vary with the flow
as by impacting electrical power con- rate.
sumption. This article will explain the
key performance factors involved in
pumping gasoline, compare and contrast
D
the different pumps that are available, ynamic head, on the other hand,
and provide information that will help is the resistance of fueling system
you maximize profits by optimizing components to movement of
pump performance. product from the tank to the nozzle. The
resistance profile of each component
causes a decrease in head or pressure as
Challenge of delivering flow the fluid passes through. Every compo-
nent that the product passes through
decreases the pressure until the pressure
F
irst, let’s consider the challenge of
providing flow consistently at or is near zero at the point of discharge. As
near the maximum permitted lev- the flow rate rises, the dynamic head
els very reliably and at a minimum cost. resistance increases at an exponential
rate. So twice
the flow gen-
erates four
times the
resistance and
requires four
times the
pressure to
move the
gasoline at a
given flow
rate. The
components
that create
dynamic flow
Static flow in a retail fueling system resistance in a retail fueling system
include the piping, accessories such as
First of all, the pump must overcome the leak detectors and safety values, and the
static head loss caused by the height a dispenser and hanging hardware such as
fluid must be lifted from tank to nozzle. the nozzles, hoses, fittings and swivels.
Dynamic head losses of components described by performance curves that
show pressure in the form of head on the
Normally, the hanging hardware gener- left or Y axis and flow rate on the bottom
ates about 2/3 of the pressure drop axis. The Y axis shows the pressure at
through the flow system and the dis- which the pump can produce the flow on
penser produces about 1/3 of the pressure the X axis. When the pump is running it
loss.
Operation of centrifugal pumps
T
he vast majority of pumps used in
retail fueling systems are centrifu-
gal pumps which create pressure
to overcome static and dynamic head by
accelerating fluid from the center of a
spinning impeller to the outer perimeter.
They typically have several stages, each
of which is primarily made up of three
parts. The impeller is spun by the motor
while fluid enters its central eye and is
accelerated to the perimeter where it then
enters the diffuser. The diffuser converts How a centrifugal pump works
the velocity of the fluid to pressure then
directs fluid, into the eye of the next supplies the flow it can against the pres-
stage’s impeller. The diffuser plate, along sure it experiences in the flow system.
with the diffuser, enclose the impeller to Changes in upstream components to
form each stage. About 14-15 psi is creat- reduce frictional pressure will improve
ed in each stage in 60 Hz pumps while 50 overall system flow by reducing the
Hz pumps typically generate 9-10 psi per amount of pressure the pump must over-
stage. come to deliver flow at the nozzle. As the
pressure requirement decreases, the
The performance of a pump is typically amount of flow a pump can deliver
increases. With a lot of pressure against to provide a given flow at one particular
the hose there is very little flow. As the dispenser while other dispensers may
pressure against the hose is relaxed, the deliver higher or lower flow depending
flow increases. The flow capacity of a on branching and pressure drops within
pump can be increased by increasing its the distribution system. Variable speed
speed by using a higher speed motor, pumps typically cost $2200 and the vari-
increasing its diameter, or increasing the able speed controller costs around $820
width of its vanes. in case it needs to be replaced.
Fixed and variable speed pumps The move towards variable speed pumps
raises concerns about electromagnetic
Fixed speed pumps are the default choice
interference (EMI), interference by elec-
for retail fueling systems. A 2-hp fixed
tromagnetic signals that can cause
speed pump typically operates at a pres-
reduced data integrity and increased
sure of about 45 psi when delivering
error rates on transmission channels in
below 20 gpm flow. Some type of flow
wireless equipment. The variable speed
limiter may be needed to meet
motor controller controls the speed of
Environmental Protection Agency regula-
the pump by generating alternating cur-
tions that mandate a 10 gpm flow rate
rent at the frequency that corresponds to
restriction to avoid overtaxing the
the desired motor speed. The controller
onboard carbon canisters used to capture
rapidly switches current, which can pro-
vapors. Both mechanical and software
duce both conducted and radiated emis-
based flow limiters are available that con-
sions as an unwanted byproduct. These
trol flow at the nozzle. This approach
emissions could potentially interfere with
provides maximum flow for every cus-
other electrical equipment operating at
tomer. At a typical cost of $1500, fixed
the station.
speed pumps are economical to purchase.
They are economical to install, because
While industrial controllers such as vari-
they do not require shielded cable, and
able speed pump controls are not
have proven to be less expensive to main-
required to obtain FCC certification,
tain.
Veeder-Root has proactively addressed
this concern by designing the Red Jacket
Variable speed pumps have multiple pro-
variable speed pump to minimize EMI
grammable set points that allow them to
and obtaining FCC certification. Veeder
maintain a single output pressure over a
Root engineers carefully designed the
wide range of flow rates. The motor
unit to keep noise levels substantially
speeds up or slows down in reaction to
below requirements for consumer prod-
the varying system flow requirements.
ucts. As a result, the pump was awarded
The variable speed pump delivers fuel at
FCC Class A certification for radiated
a relatively constant pressure until it
emissions in the 30 MHz to 1000 MHz
reaches a point where the load is too
frequency range and conducted emis-
great and the pressure begins to drop rap-
sions in the 150 KHz to 30 MHz range.
idly just like a fixed speed pump.
Variable speed pumps normally do not
require flow limiters because they deliver
gasoline at a lower pressure at low
demand. Controlling flow at the pump is,
however, less accurate than at the dis-
penser because you can only set pressure
Pressure curves for 2 hp pumps Jacket pump maintains pressure better as
the flow increases. The difference
Flow and electrical efficiency becomes particularly noticeable in the
comparisons range between 30 to 70 gpm. The Red
Jacket maintains the set pressure up to 60
gpm while the FE Petro pump pressure
W
hile all variable speed pumps
dropped below the set pressure when the
follow these basic principles
flow reached 30 gpm. This substantial
there are some important dif-
difference in performance can have a
ferences between the different models
major impact on fuel delivery. For exam-
that are available. The Veeder-Root Red
ple, the 2 hp Red Jacket pump will sup-
Jacket P200U20-2 variable speed 2 hp
ply about 10 cars fueling simultaneously
pump and Veeder-Root Red Jacket fixed
at an average of 7 gpm while the FE Petro
speed 2-hp pump were tested along with
pump can supply only 8 cars at the same
the FE Petro IST MagVFC 2 hp variable
rate.
speed pump by Jairus D. Flora, Ph.D.,
consulting statistician. Both variable
The testing also demonstrated that both
speed pumps were set to an operating
the Red Jacket fixed speed and variable
pressure of 30 psi. The graph above
speed pumps are relatively equal and
shows the pressure achieved by all three
superior to the FE Petro. 2 hp variable
2 hp pumps as flow rate increases. The
speed pumps in energy efficiency. When
fixed speed pump operates a higher pres-
the pumps were set at 25 psi in the test
sures in the lower flow range and behaves
setup, the 2 hp fixed speed pump deliv-
in a similar way to the variable speed
ered 65.4 gpm or 28.4 gpm per watt. The
pumps as flow rate increases. The two
Red Jacket variable speed pump delivered
variable speed pumps provide a similar
26.8 gpm per watt while the FE Petro
pressure of just over 30 psi in the flow
variable speed pump delivered 25.6 gpm
range from 0 to 30 gpm. But the Red
per watt.
two 2 hp variable speed
pumps in tandem. Two tan-
dem 2 hp pumps are typically
configured in a slave and mas-
ter configuration so that only
one pump runs until the
demand becomes so large that
it cannot maintain the set
pressure. Then the second
pump is activated and main-
tains the pressure until the
maximum for the tandem
configuration is reached. The
two pumps can be used in a
single tank or in two separate
tanks.
The 4 hp variable speed
pump, on the other hand, is
configured much like the 2 hp
pump but with a larger motor.
While you might expect per-
formance to be similar for
these two alternatives, actual-
ly either of the two tandem
Flow and electrical efficiency configurations provide a substantially
higher flow rate. The reason is that near-
Providing high volume fuel delivery ly all gasoline tanks have a four-inch
diameter opening into which the pump is
S
ometimes 2 hp motors are not suffi- inserted. Designing the pump within a
cient to provide consistent fuel four-inch diameter packaging constraint
delivery performance for some very creates a constriction where the product
high volume stations. At a flow of 60 comes up the inlet and passes between
gpm with either 2 hp variable or fixed the motor and outer shell of the pump.
speed pumps, pressure drops below 30 This constriction point means that dou-
psi, which means that customers will see bling the motor’s power produces consid-
substantially slower fuel flow. Customers erably less than twice the flow rate.
are usually unhappy when they see the
meter running slowly because it means Let’s look at the test results. The figure
they have to spend more time at the below shows the pressure delivered by
pump. Station owners and managers also the FE Petro 4 hp variable speed pump
prefer high throughput because it means and the Red Jacket tandem configuration.
higher revenues. Note that the tandem configuration
maintains operating pressure at a consid-
The three options to provide fast fuel erably higher flow rate than the single 4
delivery to more than 10 dispensers are hp pump. The Red Jacket tandem config-
1) using a 4 horsepower variable speed uration produced a flow of 141 gpm at 25
pump or 2) combining two 2 hp fixed psi compared to the FE Petro flow of 93
speed pumps in tandem or 3) combining gpm at 25 psi. When both pumps were
Pressure curves for 4 hp pump vs. 2 hp tandem
compared at a flow rate of 90 gpm, the age flow rates decreased from 9 gpm to 7
Red Jacket tandem configuration also gpm, reducing flow by over 20% and
used less power than the FE Petro 4 hp increasing filling time for the average
pump. The tandem configuration also customer by 22%. During rush hours,
offers the advantage that if a maintenance when the station was typically grid-
problem stops one pump from operating, locked, revenues were lowered by about
the other is automatically programmed to 15%. The stations also saw 5% greater
take over and run by itself. The tandem energy costs. Needless to say, the station
configuration costs about $1000 more, owner was anxious to return to the tan-
however, this extra cost is miniscule con- dem pumping configuration. These
sidering the ability of the pump to handle improvements demonstrate how paying
7 additional customers simultaneously close attention to pump performance can
means that it can easily pay back its extra increase retail fueling profitability.
cost.
The fuel delivery and power consump-
tion improvements provided by tandem
variable speed pumps relative to 4 horse-
power pumps were demonstrated recent-
ly at two high-volume stations in which
each pump delivers in the neighborhood
of 300,000 gallons per month. When the
Red Jacket tandem 2 hp variable speed
pumps were temporarily replaced with
single 4 hp variable speed pumps, aver-
