We’re all familiar with the children’s relay race that
involves a bucket of water. Teams of four or five kids start
with a full bucket of water and take turns carrying it to the
next person in line before handing it off. The catch is that,
invariably, some of the water will slosh out. The winning
team is the one whose bucket has the most water remaining
in it when it reaches the last person, since it is virtually
impossible for the bucket not to lose at least a little water.
The shipping and transfer of liquid commodities around
the world follows a similar “relay race” type of pattern.
While there is generally no spillage, not all of a specific
shipment makes its way to the final destination. Profitable
and responsible transfer relies on both speed and the
complete transfer of product. For example, let’s take a look
at petroleum products.
Crude oil is shipped by barge to a refinery “feedstock”
storage tank. After the oil is refined into its various
marketable forms, those products are shipped to “finished
goods” storage tanks. From there, they are taken by barge,
railcar or tank truck to intermediate bulk-storage facilities.
When needed, they are transferred into railcars or tanker
trucks for shipment to the end-user.
With each transfer, it’s common for a small amount of
a specific shipment to miss its final destination. This is because a “heel” is often left in the barge, railcar or tanker.
The heel is the amount of product that can’t be lifted
out of the delivery vessel by the pumping system that is
used at the business end of each link in the supply chain.
While it is next to impossible to get every last drop out
of the delivery vessel, there are pumping
technologies available that can guarantee
that as much of the shipment as humanly
possible is removed during delivery.
This white paper will focus on the
technologies that have been designed to
leave delivery vessels and storage tanks as
“dry” as possible after the transfer of a wide
array of liquid commodities.
Bang For The Buck
In any transaction, whether it’s buying a
pack of gum or a new home, you want to
get what you pay for. The same principle
holds true in the purchase of bulk petroleum
products. If a gasoline-station operator buys
6,000 gallons of premium unleaded, he
wants 6,000 gallons of premium unleaded
delivered into the underground storage tanks
at his site.
The supplier wants to deliver the full 6,000
gallons because he doesn’t want to be known
as someone who doesn’t deliver what is
promised. He also wants to empty his tanker
as completely as possible because he might
use it to ship a variety of products. If so, any
remaining fuel in his truck or piping could
potentially contaminate the next shipment it
is scheduled to handle.
Another concern with product transfer is
the discharge hoses and piping that are
used as the middlemen when the product
is being moved from a storage tank to a
delivery vehicle, or vice versa. Operators
need a pumping system that is capable of
clearing those discharge lines at the end of
the transfer process, not only to ensure that
all of the product is delivered, but also to
prevent spills, increase safety and ensure that no product
cross-contamination can take place. Additionally, no driver
wants to have to “walk down “ the delivery hoses to ensure
all of the product has been cleared from the lines.
When most people think of liquid-storage terminals, the
enduring image is one of the giant 500,000-gallon holding
tanks that dot the landscape at a petroleum refinery. In
reality, refinery storage is just the tip of
the iceberg in the liquid-storage terminal
universe. Tank farms serve as an essential link
in the distribution of a wide variety of other
products, including mainstream and niche
chemicals (solvents, fertilizers, pesticides,
acids, etc.); alternative fuels (ethanol and
biodiesel); vegetable oils for food products;
animal fats and oils for cosmetics; molasses;
LPG; and LNG.
In short, any liquid that can be transported
in bulk, whether by barge, railcar or
tank truck, at some point in its life is
transferred into and out of a storage tank
and delivery vehicle, often at numerous
points along the supply chain. There is also
growing popularity in a process known
as “transloading.” When a product is
transloaded, it is directly transferred from
one mode of transportation to another,
for example, from a railcar to a tank truck,
which eliminates the intermediate stage of
transferring the product into a storage tank.
The same principles apply in transloading as
they do in the transfer of product from barge
to storage terminal: remove as much of the
heel as possible, suck the lines dry and avoid
spillage or cross-contamination.
The pumping technology used in liquidterminal
petroleum production as an example—is
put under the most stress at the head of the
supply chain, where the barge or ship loaded
with crude oil arrives at the refinery. The first
very large crude carrier (VLCC) was built in
1966. Since then, more than 1,000 of these
behemoths—which can carry more than 2
million barrels of oil at one time—have been
built to traverse the world’s oceans as they
ship crude oil to refinery locations around the globe. These
types of supertankers were designed to be an economical
way to deliver large shipments of oil throughout the world.
When they do arrive at port, however, they need to be
unloaded. Again, the same unloading parameters apply:
the heel must be minimized, the threat of spillage must be
eliminated and cross-contamination must not occur.
Over the years, many pump technologies have been utilized
in the effort to optimize liquid transfer from ship, barge,
railcar or tank truck into storage terminals. The one pump
technology that has repeatedly been proven the most
effective in this application—for all of the many different
products that are handled in this fashion—is the positive
displacement sliding vane pump.
Sliding vane technology was invented in 1899 by Robert
Blackmer as an alternative to the inefficient gear-type
pumps that dominated the market at the time. Just by their
operation, the flow rate and efficiency of a gear pump will
erode over time as the pump’s gear teeth wear. On the
other hand, sliding vane pumps feature vanes that slide out
of the pump rotor as they wear, meaning there is no drop
in flow rate and volumetric efficiency as the pump ages.
Realizing that he had found the solution to the liquidhandling
needs of a wide variety of industries, Blackmer
incorporated his company in 1903. Today, Blackmer® is
headquartered in Grand Rapids, MI, USA, and remains the
world leader in sliding vane pumps used in the transfer
Blackmer is the standard-setter in sliding vane pump
technology. These pumps contain a series of vanes that
freely slide into or out of slots in the pump rotor. The
pump’s rotation draws liquid in behind each vane, through
the inlet port and into the pumping chamber. As the rotor
turns, the liquid is transferred between the vanes to the
outlet where it is discharged. Each vane provides a positive
mechanical and hydraulic displacement of the liquid.
The vanes are actuated by three forces: centrifugal force
from the rotor’s rotation; push rods that move between
opposing pairs of vanes; and the liquid pressure that enters
through the vane slots and acts on the bottom of the vanes.
Therefore, each revolution of a sliding vane pump displaces
a constant volume of fluid with variances in pressure
having a minimal effect. This minimizes energy-wasting
turbulence and slippage, while the pump’s high volumetric
efficiency is maintained.
Further, since the vanes constantly adjust to accommodate
for wear, the pumps maintain near-original and consistent
volumetric performance over time. A key consideration for
the liquid-terminal storage industry is that sliding vane
pumps are able to create a tremendous amount of dry
suction. This suction capability results in a pump that can
most effectively strip pipes and hoses while removing as
much of the heel as possible from barges, railcars and tank
trucks. Also, the ability of a vane pump to move air allows it to “blow down” the discharge lines. The operational
ability of sliding vane pumps also makes them the ideal
solution for transferring highly viscous liquids.
Realizing the growth in “green” operations and the
increased concern for the environment, Blackmer designs
its pumps and compressors to be the among the most
energy-efficient in the industry. This Smart Energy™
Flow Solutions program is designed to enable pump users
to gain a competitive business advantage through the
deployment of energy-saving positive displacement sliding
vane pump technology. At its most basic, Smart Energy
means controlling energy expenses, increasing operational
reliability, reducing vulnerability to energy-price volatility
and driving productivity improvements.
The liquid-terminal industry is one of the most crucial in
the world. Every day, millions of gallons of raw materials
and finished products in a wide array of industries are
transferred into and out of liquid terminals around the
globe via a variety of delivery vessels. The terminal operator
has a large number of challenges: make sure the product is
loaded and unloaded safely, for both terminal personnel
and the environment; enable the product to be transferred
in the most energy and time-efficient manner possible;
remove as much of the heel from the barge, railcar or truck
as possible; guarantee that no product cross-contamination
occurs; and do it in an environmentally-friendly manner.
For more than 100 years, positive displacement sliding
vane pump technology from Blackmer has set the standard
in meeting these parameters. That is why more and more
savvy terminal operators are turning to the sliding vane
pumps offered by Blackmer as the solution to the producttransfer
needs at their liquid-storage terminals.
Blackmer® remains the world leader in sliding
vane technology for the transfer of liquids within
storage terminal applications.
Ted Ratcliff is the Senior Product Specialist in Energy for Grand
Rapids, MI, USA-based Blackmer, an operating company within
Dover Corporation’s Pump Solutions Group (PSG™). He can be
reached at (817) 460-1369 or firstname.lastname@example.org. Downers
Grove, IL, USA-based PSG is comprised of six leading pump
companies—Wilden®, Blackmer®, Griswold™, Neptune™,
Almatec® and Mouvex®. You can find more information about
Blackmer at www.blackmer.com and PSG at www.pumpsg.com.