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Low-Pressure
Sewer System
(LPSS)
General
Description The VORTEX Grinder Pump system is designed to function as
a part of a low-pressure sewer system. These systems are designed to operate
where implementation of a conventional system is impractical, uneconomical
or otherwise not feasible. By definition, a low-pressure sewer is a small
diameter pipeline that follows the profile of the ground, buried in a
shallow trench. Each home uses an individual grinder pump to discharge
waste to the force main. The VORTEX Grinder Pump is specially designed
to grind the solids in wastewater to slurry, similar to a garbage disposal.
The positive displacement progressing cavity pump technology of the VORTEX
system is the ideal choice to reduce the waste and then facilitate its
transport across distances of up to a mile and over terrain that can vary
as much as 138 feet. The VORTEX pump is engineered to provide years of
trouble-free, reliable service for this application. In addition, the
LPSS traditionally constructed of PVC and HDPE piping, will provide years
of service collection, free of I&I, and allow the large capital costs
of treatment to be used to treat the waste from houses and not infiltration.
A
low-pressure sewer system (LPSS) is not the economical solution to all
sewer collection problems. If the front footage of the sewer area is 30'
to 60' and an outfall has no grade problems, a gravity sewer is the most
economical way to collect the sewerage and transport it to the treatment
facilities. However there are many situations when LPSS is the best was
to go. Some examples of appropriate design for LPSS are listed below:
| 1.
If an extremely environmentally sensitive area or an area of great
importance lies between an outfall and the sewer area, the units
can be serviced by Vortex pumps, each tying into one main and then
the main directionally drilled under the sensitive area. This in
turn can be connected either to an existing gravity or pressure
sewer. With the high head capacity of each Vortex pump, no additional
pumping station is needed.
2. To sewer an existing area in which the lot fronts are in excess
of 150', the cost advantage of 2"-3" collection pipe ($8 - $12/foot
installed) as compared to 8" gravity ($18 - $100/foot installed)
makes LPSS a cost effective method of design. The cost differential
in piping must overcome the grinder pump installed price of approximately
$5000 per unit.
3.
If there are partial lots in an area requiring sewage systems requiring
a gravity depth in excess of 20' because of the terrain, while the
remaining lots require a sewage system with an 8' depth gravity
line, the design engineer can be cost effective with a design of
8' depth (cost $30/foot installed) and installing several Vortex
grinder pumps to sewer the lots ($5000/unit) in contrast to running
the gravity line at a depth in excess of 20' (cost $100/foot installed).
4.
Often times a grinder unit may correct a particularly troublesome
problem. An example of this was accomplished recently in Florida.
There was 1 unit connected to a MH in an access ramp on I-95. The
MH was 35' deep, having been necked up at the time of road construction,
in the center of the ramp, and the pipe going into the MH collapsed.
A 2" discharge line was run in the existing sewer and drilled through
the collapsed pipe into the MH and a grinder pump then serviced
the unit, eliminating an extremely costly repair to the existing
sewer. |
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| 5.
Extremely flat or rugged terrain can make the LPSS cost effective.
Both types of terrain can cause the necessity of multiple pump
stations. Besides the cost of acquisition of real estate for
pumping stations and the cost of construction ($100,000 - $300,000)
and the cost of deep gravity sewers at (20' + $100/ft installed),
often times the small diameter force mains ($9 - $12/ft installed)
+ the cost of each individual grinder ($5,000/unit) is the most
cost effective and should be investigated by the design engineer.
Not all sites are designed for the LPSS, but cost savings and
land usage dictates the Design Engineer to investigate this
option. |
| 6.
All sewer authorities have run into an area where they dread an
installation because the conventional methods of construction,
causing all the disturbance inherit in this type of construction,
make the installation a nightmare. Directionally drilled 2" force
mains eliminate 90% of this disturbance and just simply make everyone's
life better. Installing Vortex pumps is an answer to their prayer.
Another cost savings to developers is the ability to defer the
on-lot pump costs until the site is built. This is especially
advantageous in areas of slow build up.
7.
All authorities have run into situations where they just run out
of cover for gravity lines and are forced to install a terminal
MH before the last few lots receive sewage systems. A small LPSS
system can be the appropriate design, cost effective system than
the costly pump station.
8.
Many low lots have remained on septic systems in the past, simply
because the house lot was too low to be sewered. A single Vortex
pump lifting the sewage to the existing gravity lines is the answer.
In other situations the unit sewered was just too far away from
the main to allow a 1/4"/foot fall service line to be used from
the unit to the sewer main. Again, a single Vortex pump is the
answer.
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