Understanding Vacuum Sewer Technology
An alternative collection system
Public works directors take a long view when they make infrastructure
decisions. The true cost of a project or technology is determined
by many factors over a period of years, often decades. Installation
costs, manufacturer support, operations, maintenance and service
are all part of the value equation.
For centuries, gravity has been the usual choice for wastewater conveyance. It
is a known system that’s relatively easy to understand. Newer technologies, like
vacuum sewers, are something of an unknown.
Public works officials who have first-hand knowledge of vacuum sewer technology
will tell you that installing and maintaining a vacuum sewer system is easy and
the service life is measured in decades. The first vacuum sewer was installed
in the United States in 1972, and 30-year-old vacuum systems are still functioning
well with minimal maintenance.
Vacuum sewers have proven to be an affordable, efficient, reliable technology.
Knowing how they function and are maintained will shed light on why many municipalities
are turning to vacuum sewers as their preferred conveyance system.
How it Works
Some may think that vacuum sewer systems are complex and fragile. In fact, the
opposite is true. Vacuum systems operate on simple principals of physics and
have proven to be extremely reliable over many years of service.
Homeowners usually don’t notice the difference between vacuum sewers and other
systems because gravity is used to transport wastewater from homes and businesses
to the first collection point, the vacuum valve pit. The valve pit is usually
buried near the street and consists of a small collection sump and a pneumatic
vacuum valve mechanism located in a chamber above the sump. Two homes are typically
connected to a single valve pit.
When the wastewater in the valve pit sump reaches a predetermined level — usually
corresponding to about 38 L (10 gal) — it triggers the pneumatic valve that releases
the wastewater into the vacuum main. In the vacuum main, negative pressure propels
the wastewater at speeds up to 5.5 m/s (18 ft/s) toward the vacuum station. The
speed of the wastewater within the vacuum main helps scour the line and break
The PVC vacuum main is laid in a sawtooth profile to ensure adequate vacuum levels
at every point along the line. Burial depths typically range from 1.2 to 1.8
m (4 to 6 ft), shallower than most gravity sewers mains. When the wastewater
reaches the vacuum station, it is collected into a tank and then pumped into
a sewer main that transports the wastewater to the treatment facility.
Vacuum stations often are designed to look like other structures in the neighborhood.
Each station contains two or more vacuum pumps, two discharge pumps and a collection
tank. A single vacuum pumping station can collect wastewater from houses located
as far as 3 km (2 mi) away. Because vacuum sewers are closed systems, there
is no odor at the station or anywhere along the vacuum main.
The technical characteristics of vacuum sewers have made them a popular option
for areas with flat terrain and high groundwater, such as coastal communities.
Many inland areas also have installed vacuum sewers for a variety of reasons,
including environmental concerns. Because vacuum sewers are a closed system
under pressure, groundwater can’t enter into the system and wastewater can’t
leak into the environment. If a leak occurs within the collection system,
monitors at the vacuum station alert system operators.
Vacuum sewers are a good option for established neighborhoods, too. Vacuum mains
require relatively shallow trenches, so there is typically less traffic disruption,
less excavation, and less dewatering. Vacuum lines also can be rerouted easily
around underground obstacles, usually without change orders. Communities transitioning
from septic tanks to a central sewer system have found vacuum technology appealing
because vacuum system installation creates less neighborhood disruption. Municipalities
with gravity sewers can add vacuum sewers to their collection system with little
or no problem.
Depending on geographic conditions, vacuum sewer design and
installation can be different than gravity sewer installation.
Vacuum pressure in the collection lines moves wastewater without
the benefit of gravity. Therefore, slope is a less significant
factor in vacuum sewer design. The shallow depth of the vacuum
main helps reduce installation cost and disruption during installation.
It’s also easy to make last-minute changes during pipe installation.
If an unexpected underground obstacle is encountered, the vacuum
main is simply re-routed around it; change orders are usually
“AIRVAC developed most of the specifications used in our vacuum system design,
so it was good to have their expertise at the job site. They have worked with
us to create a system that works very well and requires minimal maintenance,”
said Don Eckler, P.E., president of Eckler Engineering, whose firm helped design
a vacuum sewer system in the Florida Keys. Airvac is a vacuum sewer manufacturer
based in Rochester, Ind.
Field service technicians serve as a liaison between the contractor, engineer,
and owner. Their experience and knowledge of vacuum sewer technology ensures
maximum system efficiency, secure connections and more importantly, they provide
experienced advice if installation problems arise. This type of service helps
reduce installation time and cost, and above all, ensures the system is installed
Vacuum sewer technology is easy to understand once you see
it in operation.
Ernie Wilson, general manager for the Fripp Island, South Carolina, Public Service
District, was skeptical of vacuum sewers until he saw the technology first hand
and received instruction on the operation and maintenance of the system.
“We went to the manufacturer’s headquarters in Indiana and we visited some cities
with vacuum sewer installations. “The training we received was outstanding,”
he said. “They taught our staff how to install valves and all other aspects of
Once the system is installed, system owners can choose their level of service
from the manufacturer. A field service technician is available for as long as
necessary, even permanently, to help train public works staff on how to maintain
the system or to provide everyday system maintenance.
JEA, the electric, water and sewer utility for Jacksonville, Fla., chose to have
their staff trained on-site by a field service representative. According to Chuck
Martin, JEA’s maintenance coordinator, it was the right decision for his utility.
“The training we got from the manufacturer was excellent,” said Martin. “They
were very thorough. They taught us how to perform routine maintenance on the
vacuum pumps about once a week. I can’t recall a single instance where we’ve
had to repair any part of the vacuum sewer infrastructure.”
Other municipalities and sewer districts have chosen to contract
with system manufacturers to provide temporary and/or ongoing
system maintenance. The Tri-Lakes Regional Sewer District in
Columbia City, Indiana, has approximately 1800 customers, making
it one of the 10 largest vacuum sewer systems in the United
A contract maintenance agreement was a perfect solution for Tri-Lakes, said
Nel Mann, Tri-Lake’s district administrator
“The field service technician did a great job of managing our system for an extended
period, making some necessary system adjustments, and training our on-site personnel,”
she said. “We are extremely comfortable knowing that they are always just a phone
After more than a decade of contracting the operation and
maintenance services to a local maintenance company, Tri-Lakes
decided to operate and maintain their system themselves. They
signed a 6-month contract with AIRVAC to take over daily operations
and maintenance responsibilities and to train their new employees
so they could eventually provide operations and maintenance
“A well-qualified AIRVAC service technician was assigned to us for a 6-month
period,” explained Nel Mann, Tri-Lake’s district administrator. “During this
time, he not only responded to service calls, he also trained our new employees
on the technology and fine-tuned our system. At the end of his 6 months, our
vacuum sewer system was running better than ever and our employees were well
trained to keep it that way.”
Even communities that prefer servicing their own vacuum sewers
have found the process to be easy, efficient and safe. Because
vacuum sewers are closed systems, workmen rarely come in contact
with wastewater. Vacuum stations are clean and odor free; and
daily system checks take only a few minutes. If a vacuum line
is accidently cut or damaged, the leak is easy to locate and
can be repaired within a few hours with minimal digging or
“One thing that struck me from the beginning was the simplicity
of the vacuum system,” said Robert Holland, utilities superintendent
for the City of Groveland, Florida. “I expected a lot of technical
issues, but we were trained on the system in a matter of a
few days. It is really a very simple system, which was a pleasant
Holland said it takes a maintenance staffer 15 minutes a day
to check the gauges at the vacuum station. If a vacuum valve
ever becomes stuck in the open position, it can be fixed in
less than five minutes. He noted that the vacuum valve pits,
which operate pneumatically and require no electricity, are
easily accessible and simple to understand.
PARTS AND SERVICE
As part of a routine maintenance plan, utilities choose to have their vacuum
system vendors provide an annual or bi-annual system evaluation. Technicians
visit to monitor and analyze your system’s performance and make necessary recommendations.
This can help prolong the life of vacuum components and ensure uninterrupted
service to customers.
This article appeared in the May 2011 issue of WE&T. If you
would like to read the entire story as it appeared in the magazine, you
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to Special Themed Articles page.