Ensuring Pump Performance –
Even Under Water
Baltimore County has dozens of sewerage lift sta- tions in low lying areas throughout the county. They vary in size but are fairly consistent in design, resembling small one-story brick houses with pumps, motors and valves located in the basement. Electric controls are
upstairs on the ground floor level. Although this is a nice, compact design, it was susceptible to being knocked offline during
flood events when water would short circuit the pump motors.
About a decade ago, city officials began a county-wide
program to upgrade every lift station to make it resistant to
flood damage. The rehab consisted of replacing every conventional pump with a dry/wet submersible pump and motor.
Now, even if there is a flood and the basement fills with water,
the pumps continue operating without missing a beat. Some
of these basements are several stories underground but the
pumps operate reliably even at depths approaching 100 feet.
It became apparent, however, that the control system that
monitors pump operation was a weak link. Every pump had
a pressure switch on the discharge to monitor output pres-
sure. If a rag or other foreign object became tangled in the
impeller, the pressure switch would signal an alarm condition.
But during flood events these controls would short out and
shut the station down, leaving the submersible pumps literally
dead in the water. Another problem with the pressure switch-
es were the diaphragm seals. They were supposed to protect
the switch from the raw sewage, but they would become im-
pacted with solids, causing the switch and gauge to seize.
A two-step response provided the solution for both of these
problems. The first step was to replace the conventional diaphragm seals with Onyx Isolator Rings, which drop between
flanges like a wafer-style valve. The inner surface is a rubber
cylinder that matches the ID of the adjacent pipe. It provides
a smooth, unobstructed path for the sewage, making it absolutely impervious to clogging. Behind the rubber cylinder is
an inner tube filled with silicone instrument oil that transmits
pressure to the gauge and switch.
The second step was to replace the pressure switches with
submersible level transmitters. Upstairs in the electrical control room, each pump has a receiver
with a digital read out and alarm relay. Now, instead of just getting an
alarm signal, plant operators can actually see the exact discharge pressure of each pump, enabling them
to monitor pump performance on a
In the years since the upgrade,
these lift stations have repeatedly withstood flooding. The pumps
and pressure controls have operated
perfectly, without interruption, even
while under water for weeks at a
Onyx Valve Company is a manufacturer of pinch
valves, check valves, and pressure sensor rings.
Backed by 20 years of experience in the flow control industry, the company prides itself on the durability and longevity of its products, which are
manufactured and assembled in the U.S. For more
information, visit www.onyxvalve.com.
Circle No. 252 on Reader Service Card
Four-inch Isolator ring with gauge and submersible pressure transmitter monitor pump performance
several stories beneath the streets of Baltimore County, Md.