Mechanics of the Grand Coulee Dam
incorporated six Vanton sump pumps to
ensure reliability and operation of
three 805 megawatt turbines.
Grand Coulee Dam Uses
Six Cantilever Pumps to
Ensure the Reliability of
Three 805 Megawatt
Power, Energy and Utility
Grand Coulee Dam
SUMP-GARD Thermoplastic Vertical Pump
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Reprinted from WATER & WASTES DIGEST
G. Michael Stromback, Senior Mechanical Engineer
With an installed capacity of 6,809 megawatts, the Grand Coulee Dam
located on the Columbia River in the state of Washington is the largest
hydro project in North America.
For a short time following its completion, it was known as the largest
hydro project in the world. Measuring more than a mile long (1.6
kilometers) and 550 ft tall (167.6 meters), it is the biggest concrete
structure ever built, containing nearly 12 million cubic yards (339,847
cubic meters) of concrete.
Lake Roosevelt, which stretches out behind the dam, is approximately
150 miles (241 kilometers) long as it extends up the Columbia River to
the Canadian border and to the Spokane River within 37 miles (60
kilometers) of the city of Spokane. As such, Lake Roosevelt contains
more than five million acre-feet (6,167,409,188 cubic meters) of active
The Grand Coulee Dam releases, on average, 110,000 cubic feet
(3,114.85 cubic meters) of water per second, primarily for generating
electricity. Controlling high volumes of water requires giant-sized
equipment, which can sometimes face giant-sized problems when
Three of the 24 turbines are rated at 805 megawatts and are some of the
largest turbines ever built. Making sure they consistently function in a
reliable manner can present significant hurdles for maintenance
engineers and mechanics.
Spotlight on the problem
Mentioned above, three of the turbines, Units G-22, G-23, and G-24,
each are rated at 805 megawatts. Their main turbine shaft is
approximately eight feet in diameter with shaft seals that consist of a set
of braided packing rings, held in place by a gland within the stuffing
box. Water supplies cooling and lubrication for the packing through a
standard lantern ring located in the middle of the packing set. Leakage
during operation is to be expected.
Further, the amount of leakage increases as the packing wears and ages.
This leakage collects in the turbine pit and has to be pumped out
periodically; otherwise it could damage the turbine.
The original design for turbine pit drainage provided for two 200-gpm
pumps, one designated as the lead pump and the other as backup.
These pumps were controlled by a multi-step float switch system. If the
leakage became severe, exceeding the ability of the pumps to keep up,
the generator would have to be shut off.
Because it is highly undesirable to shut off the generator, maintenance
personnel placed additional, small, submersible pumps to remove water
from the turbine pit. The discharge from the pumps was sent to gravity
drains or to adjacent units with less leakage.
The amount of packing leakage varies, depending on the unit load as
well as other variables. Thus, the additional pumps are not needed all
the time. When the water level eventually falls below the pump
impeller, the seal in the suction cavity is broken. All cooling and
lubrication provided by the water stops and the pumps overheat and
burn up. The problem can be exacerbated by the fact that the added
submersible pumps are not always visible to operations personnel.
To make matters worse, the water that comes out of the packing area
mixes with water leaking out of wicket gates and other mechanical
seals. As a result, the water often contains grease, rags and oil that
sometimes clog up the added pumps.
One of the mechanics based at the Grand Coulee Dam suggested
replacing one of the small pumps with a bearingless Vanton
cantilever-shaft pump, which was specifically designed to operate under
extended dry-run conditions. Because it incorporated a vortex pump
head configuration to handle foreign objects without clogging, it was
put to the test.
The original intent was to use it as a backup pump, which operators
could simply start and leave running when one of the turbine units
experienced severe leakage. To the surprise of the Grand Coulee Dam
operators, the 600-gpm Vanton Sump-Gard® SGK polypropylene pump
quickly drained the entire pit and handled the contaminated water
without any problems and without the risk of damage associated with
dry running conditions.
Because of the positive results, the Grand Coulee Dam retrofitted all
three 805 MW turbines to use the cantilever pumps. There are two
Vanton SGK pumps in each of the turbine pits, connected to a
multi-stage float system that alternates running time. Although each
pump is able to completely drain the pit, they are instrumented with
level controls so the idle pump will kick in should the volume of the
water in the pit get too high. These are the specifications for the
installed pumps that have been providing uninterrupted, dependable
service for the past two years.
To address the problem faced by the water leakage at the Grand Coulee
Dam, various design specifications were indicated. For example,
engineers required a rugged, thermoplastic vertical pump with
cantilevered shaft and dry running capability that had no bearings
immersed in the pump fluid.
The pump required a large diameter alloy steel shaft isolated from the
fluid by a thick-sectioned thermoplastic sleeve and heavy-duty external
hall bearings above cover plate, housed in epoxy-coated cast iron
motor bracket to accommodate NEMA, IEC and European standard
motors. All immersed pump parts and hardware were made of
homogeneous thermoplastics so that no metal or thermoset
composites are in fluid contact.
Finally, it was required the pump have a dynamically balanced
semi-open impeller with embedded, molded-in stainless steel
reinforcing insert and a vortex pump head to handle foreign objects
Close-up of one of the six Thermoplastic
Cantilever SGK sump pumps with dry-run
Sump-Gard® SGKThermoplastic Cantilever
Bearingless Vertical Pump
In the 1950, Vanton developed a revolutionary all-plastic pump for use in conjunction with the first heart-lung device. The design limited fluid contact to only two non-metallic parts: a plastic body block and a flexible liner. This was the birth of our Flex-I-Liner rotary pump. Its self-priming sealless design made it an industry standard for the handling of corrosive, abrasive and viscous fluids as well as those that must be transferred without contaminating the product. Vanton now offers the most comprehensive line of thermoplastic pumps in the industry.
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Unit 4, Royle Park
Congleton CW12 1JJ