Aug 06, 2003

Smooth Operators

Duck Creek Wastewater Treatment Plant notices improvements due to use of electric actuators

When the Garland, Texas-based Duck Creek Wastewater
Treatment Plant experienced a problem with erratic pressure control in their
aeration blower system, they relied upon modulating electric operators to
smooth out the process excursions.

Because the Duck Creek Wastewater Treatment Plant is a trickling
filter/solids contact facility, it is permitted to treat 30 million gallons per
day. Consequently, it is essential that the plant operators maintain a high
level of plant performance--a critical parameter.

Lonnie White, instrument specialist at the Duck Creek
facility, contacted The Eads Company when it came time to upgrade the
automation of a number of existing 10-in., high-performance butterfly valves.

After reviewing products eligible for the upgrade, White
elected to use the Bettis EM800 quarter-turn, 110-volt AC electric actuator
manufactured by Emerson Process Management of St. Louis, Mo.

Flat liners

In years past, other operators at the Duck Creek facility
had struggled to get consistent control of their waste activated sludge system.
It is well known within the industry that maintaining a "flat line"
flow control is dependent on both accurate pressure control at the inlet air
blowers, as well as precision at the flow control valves to the basins.

As the Garland plant personnel struggled with sensitive
"smart" pneumatic positioners on their vane-style actuators--due to
moisture problems in the air system and on the local keypad--the Bettis
electric actuators with integral electronic positioned were installed and
hooked up to the existing 4-20 mA DC control signal. These packages included an
integral mechanical brake that ensures the valves stay in their demand position
when the signal is unchanging.

Since their installation, the performance of the actuators
has allowed for maintenance-free operation for over three years.

Based on this past performance, the plant recently purchased
three identical electrical actuator packages to replace cumbersome 480 V.A.C.
electric actuators that are currently on their 8-in. and 10-in. flow control
butterfly valves.

Prior to the decision to upgrade, operators had been running
this particular system in the manual mode because the old actuators have poor
control characteristics and high downtime due to undependable motor starters,
which are relied upon to start, stop and reverse the 480 V.A.C. actuator

This problem may be eliminated as the new actuators' 100%
duty cycle motors allow the customer to feed a constantly changing control
signal without fear of overheated motors, circuits and starters. The integral
on-board heater and thermostat help ensure no moisture is accumulated within
the housing, prolonging actuator life.

It is no coincidence that the Duck Creek Treatment Plant has
received EPA recognition for "Excellence in Operations and Maintenance."

By incorporating innovative solutions, the Duck Creek
Wastewater Treatment Plant is able to operate effectively, efficiently and

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For further information, phone Emerson Process Management at 314/553-2000.