Monterey Regional Water Pollution Control Agency (MRWPCA)
has installed a new type of pump featuring a unique, self-cleaning impeller to
overcome frequent clogging experienced in recent years at Pacific Grove Station
12. Prior to replacing the station’s two original pumps, the
wetwell’s limited retention and close proximity to Monterey Bay —
60 ft. away — increased the risk of bypasses reaching the beach, recalls
Mark Malanka, program coordinator with the MRWPCA’s Field Maintenance
Division. The City of Pacific Grove, Calif., is one of several municipalities
that contract with MRWPCA to maintain their lift stations.
“Station
12 experienced increased clogging, parts failures and general deterioration
during the years immediately prior to the pump replacement,” Malanka
noted. “Six or more times a year the impellers would become clogged,
setting up emergency situations. In addition, we had to dismantle and clean the
pumps about every six months when they became caked with grease, straws and
other residue in the waste from the many restaurants and bars in the area.
Maintenance was made even more difficult by a lack of replacement parts for the
old pumps.”
The station was designed 20 years ago as a plug flow dry
side/wet side facility with an 8-in. wetwell inlet and 6-in. outlet on the
force main side. The drywell of the 20-ft. deep facility was equipped with two
300-GPM pumps with constant-speed motors.
The coastal
communities in this area of Central California have since undergone tremendous
population growth and development. Under typical summer conditions, the pumps
could still handle the flow and ran approximately six hours per day. However,
during the winter months, the station’s old pumps could not handle the
additional 20 in. of rainfall. A trailer-mounted, 1.1-MGD auxiliary pump was
often staged nearby for additional standby capacity during periods of peak
flow.
Over a period of four years the station’s increasing
structural deterioration, blockages and generally high maintenance and
operating cost set the stage for the recent upgrades. MRWPCA convinced the city
to commit $30,000 to cover labor charges, the state-of-the-art pumps, a new
control panel, and associated upgrades to the emergency generator, level system
and modified bypass system.
Shape, Inc., a distributor for ITT Flygt pumps, assessed the
situation and recommended replacing the old pumps with ITT Flygt Model N-3127
units. The recently developed N-pumps feature a hydraulic design that ensures
efficient pumping over prolonged periods of continuous operation. The innovative design of the
self-cleaning impeller greatly reduces the risk of clogging by its ability to
maintain unobstructed impeller-vane leading edges. Laboratory tests and field experience reveal that most pump
clogging begins with the fouling of the leading edges of pump impellers. During
operation, each leading edge of the rotating “N” impeller passes
across a sharp stationary relief-groove once per rotation, ensuring that rags,
stringy materials and solids are cleaned from the impeller and pumped away.
Retrofit installations utilizing variable speed N-pumps have
not only eliminated chronic pump clogging problems, but also have delivered
energy savings as great as 50%. Increased efficiency translates into lower
overall energy consumption, a significant factor in reducing the whole-life
cost of a pumping station. Shape’s field technicians also recommended
substituting the existing 300-GPM units with 500-GPM N-pumps.
“As it turned out, it only cost us $6,000 to replace
each pump versus the $3,000 apiece to just repair the bowls at the bottom of
the wetwell on two earlier occasions,” Malanka said. “We have not
had a clogging problem or threat of a bypass since the new pumps were
installed,” Malanka said.
“The 500-GPM units run about an hour less per day
during summer months and 25 percent less during peak winter run times than the
previous 300-GPM pumps. We have therefore gained greater reliability and better
overall operating efficiency, Malanka added.”
For additional information phone ITT Flygt at 203-380-4700.
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