Vacuum sewer system

A vacuum sewer system and a method of operating such system is disclosed. The system includes a sewage holding tank and a lateral flow line and a vacuum valve associated with the holding tank for permitting a quantity of wastewater to be drawn out of the holding tank by a vacuum environment. The wastewater is drawn through the lateral flow line and a main pipeline to a desired collection location. A plurality of air inlet valves are arranged at spaced locations along the main pipeline for facilitating the flow of wastewater through the lateral flow line so that a large volume of the wastewater can flow through the lateral flow line in a given time.

FIELD OF THE INVENTION 
The present invention relates to vacuum sewer systems. More particularly, 
the present invention relates to a vacuum sewer system including a vacuum 
valve which will permit substantially only sewage to flow from a sewage 
holding tank into a vacuum environment wherein the rate of sewage flow is 
enhanced by utilizing a plurality of air inlet valves spaced along the 
main pipeline of the sewer system. 
BACKGROUND OF THE INVENTION 
Several types of wastewater collection systems are utilized in commercial 
and residential environments. These systems include a conventional gravity 
sewer flow system, a pressurized system which utilizes positive pressure 
pumps to facilitate sewage flow and vacuum sewer systems. 
In a conventional gravity sewer system, the gravitational forces are 
utilized to induce sewage flow. The structure of a gravity sewer system 
must be such that the liquid flows from an initial storage tank at a 
relatively high elevation to a sewage collection area at a lower 
elevation. The pipeline in a gravity sewer system must have a sufficiently 
steep slope so that the sewage and water flows therethrough with enough 
velocity to create a self-cleansing affect. Gravity sewer systems are not 
cost effective wherein the topography is such that the pipeline cannot be 
arranged at a sufficiently steep slope to accommodate the required sewage 
flow. 
Positive pressure sewer systems may be used in certain environments wherein 
gravity sewer systems are not cost effective. Positive pressure sewer 
systems require the use of one or more pumps located at various wastewater 
input points so that sewage flow may be maintained by pumping the sewage 
into a network of relatively small diameter pipelines. Positive pressure 
systems can also be used in conjunction with a gravity system wherein at 
least one check valve is arranged at each pump location to serve at the 
interface between the gravity system which may be utilized at an 
individual residence and the pressurized system which may be arranged at a 
remote location, such as under a nearby street. 
The third major type of a wastewater treatment system is a vacuum sewer 
system which may also be referred to as a negative pressure system. In its 
simplest form, it may include a vacuum collection tank and a vacuum pump 
located at a collection or pumping station, an initial sewage holding 
tank, a main pipeline for transporting the sewage from the holding tank to 
the collection station, and a vacuum valve arranged between the sewage 
holding tank and the main pipe line. A lateral pipeline which usually has 
a smaller inner diameter than the main pipeline is arranged between the 
vacuum valve at the sewage holding tank and the main pipeline. 
The vacuum valve may be electrically or pneumatically operated and usually 
serves as an interface between a conventional gravity plumbing system 
which may be used to transport sewage to the sewage holding tank and the 
vacuum portion of the sewer system. Prior art vacuum sewer systems 
required that a predetermined ratio of wastewater, which may contain both 
liquid and solid sewage within a water or chemical-based medium, and air 
be drawn from the sewage holding tank and the outside environment into the 
main vacuum pipeline. The wastewater and the air were then forced 
downstream toward the sewage collection station by the pressure 
differential between the sewage collection tank and the sewage holding 
tank. The pressure differential exists due to the evacuation of air from 
the collection tank by using vacuum pumps, such that the collection 
station end of the main sewage pipeline is at a lower absolute pressure 
than the atmospheric pressure which normally exists in the sewage holding 
tank. In other words, the pressure differential creates a hydraulic energy 
gradient from the sewage holding tank toward the collection station. The 
hydraulic energy differential drives the wastewater through the open 
vacuum valve and the connected lateral line and into the main vacuum 
pipeline towards the collection station. 
Operation of vacuum sewer systems is limited by the total pressure 
differential which may be created between the collection station and the 
atmospheric pressure at the sewage holding tank. The theoretical upper 
limit of the pressure differential is between the existing barometric 
pressure and absolute vacuum. This limit may be quantitatively defined as 
760 mm Hg which is approximately equivalent to the pressure exerted by one 
atmosphere, or 34 feet of water. Practically, this upper limit of the 
pressure differential cannot be obtained as absolute vacuum is an ideal 
state. Typical pressure differentials in conventional vacuum sewer systems 
range between 200-600 mm Hg. 
The air that was admitted by the vacuum valve into the associated piping 
network was necessary to facilitate the flow of wastewater through the 
system. However, the air took up a certain volume which effectively 
limited the volume of wastewater which could be drawn into the sewage 
pipeline at a given time. 
In certain prior art systems, an air inlet valve was arranged at remote 
locations along the main pipeline to facilitate the wastewater flow 
through problem areas on the pipeline, such as "sags" and "high lift" 
regions. The sags resulted due to the profile of the associated pipeline 
which followed the ground surface contour. A sag may result when the 
pipeline directs the wastewater flow at a downhill angle and then requires 
the wastewater to flow slightly uphill. A sag may be considered the radius 
area between the downhill and the uphill slope of the pipeline. The 
pipeline may retain wastewater in these sags, thus hindering overall 
wastewater flow. The use of an air inlet valve at a sag region in the 
pipeline was found to be efficient to force the wastewater which may 
otherwise be retained in the sag to flow through the pipeline. 
With regard to a high lift application, it was found that the use of an air 
inlet valve at a location along a main pipeline that extended upwardly at 
a relatively steep angle, helped to facilitate the flow of wastewater 
through the pipeline at the high lift region. 
In conventional vacuum sewer systems, where both air and wastewater are 
conveyed through the lateral lines, the flow rate of wastewater through 
the lateral sewage pipeline is typically limited to approximately 15 
gallons per minute (GPM). This flow rate may be inadequate for various 
commercial and residential applications which require handling of large 
amounts of wastewater. The present invention overcomes the problems 
associated with inadequate wastewater flow through lateral and main 
pipelines of a vacuum sewer system. 
SUMMARY AND OBJECTS OF THE INVENTION 
In accordance with a first aspect of the present invention, a method of 
operating a vacuum sewer system for withdrawing wastewater from a sewage 
holding tank through a lateral flow line and into a main pipeline is 
provided. The method preferably comprises the steps of creating a vacuum 
environment in the main pipeline and the lateral flow line. Selectively 
subjecting the wastewater within the sewage holding tank to the vacuum 
environment for a period of time sufficient to force substantially only 
wastewater retained within the sewage holding tank to flow into the 
lateral flow line but insufficient to permit an appreciable amount of air 
to flow therewith. Air may then be selectively admitted directly into the 
main pipeline to increase the volume per unit time of the wastewater 
flowing in the lateral flow line. 
When performing the step of creating a vacuum environment, it is preferable 
to activate at least one vacuum pump that is connected to the main pipe 
line until the predetermined vacuum environment is created within the main 
and lateral lines. Preferably, the vacuum environment created within the 
main and lateral lines is between 200 mm Hg and 600 mm Hg. 
In a preferred embodiment, a programmable logic controller (PLC) is used to 
perform the steps of selectively opening and closing the vacuum valve 
means. This is accomplished by sending control logic signals from the PLC 
at predetermined timed intervals to the vacuum valve means. The PLC may 
also be used to perform the steps of selectively opening and closing the 
plurality of air inlet valve means. In accordance with these steps of the 
present method, control signals may be sent from the PLC at predetermined 
timed intervals to selected ones of the plurality of air inlet valve 
means. 
In another preferred embodiment, level detection means may be used to 
ascertain when the vacuum valve means should be opened or closed to allow 
substantially only wastewater stored within the sewage holding tank to be 
exposed to the vacuum environment. The level detection means may comprise 
a floating-type sensor, a pneumatic device such as a bubbler system, an 
ultrasonic detection device or the like. The level detection means may 
operate in conjunction with a PLC, or may operate independent of the PLC. 
In an embodiment which uses level detection means, a control signal is 
generated to actuate the vacuum valve means to open when the level of 
wastewater within the sewage holding tank reaches a predetermined value. 
In this embodiment, a control signal is also sent to the vacuum valve 
means to effect closing thereof when the level of wastewater within the 
sewage holding tank goes below a predetermined value. 
The method of operating the present vacuum sewer system may also include 
the step of actuating the vacuum valve means to cycle between open and 
closed positions until a desired amount of wastewater initially stored 
within the sewage holding tank has been evacuated therefrom. 
A PLC may be used to automatically activate associated vacuum pumps to 
create a desired vacuum environment when the wastewater within the sewage 
holding tank reaches a predetermined level. This may be the same PLC used 
to selectively open and close the vacuum valve means and the plurality of 
air inlet valve means. 
The present method could also be operated with a sewer system which is a 
combination of a gravity plumbing system and a vacuum system. In this 
environment, the method may include the steps of selectively transporting 
wastewater under a gravity flush system from an initial storage tank 
through corresponding gravity lateral lines into the sewage holding tank 
prior to exposure to the vacuum environment which occurs upon actuation of 
the vacuum valve means to an open position. 
In accordance with another aspect of the present invention, a vacuum sewer 
system is provided. The vacuum sewer system preferably comprises a sewage 
holding tank and vacuum valve means which is normally arranged in a closed 
position and is selectively actuated to an open position. The vacuum valve 
means is operatively connected for fluid flow with respect to the sewage 
holding tank to selectively permit substantially only wastewater stored 
within the sewage holding tank to flow therefrom while preventing any 
appreciable amount of air from flowing out of the sewage holding tank. 
Lateral flow line means are provided for transporting wastewater out of 
the sewage holding tank. The vacuum valve means is connected to the 
lateral flow line means and is operatively associated therewith. The 
vacuum valve means may be arranged either upstream or downstream of the 
lateral flow line means. A main pipe line is arranged downstream of the 
lateral flow line means and is adapted to receive wastewater flowing 
therefrom. Vacuum generating means are provided for generating a vacuum 
environment within the main pipeline and the lateral flow line means. A 
plurality of air inlet valve means are arranged at spaced locations along 
the main pipeline and are selectively actuatable from a closed to an 
opened position and vice versa for selectively permitting ambient air to 
be drawn into the main pipeline by the vacuum environment therein, whereby 
the capacity in terms of the volume per unit time for wastewater flowing 
within the lateral flow line means is increased from an initial amount to 
a greater amount. 
The lateral flow line means may comprise a flexible hose which may be 
connected to the sewage holding tank and a fixed lateral flow line, which 
may comprise a substantially rigid structure, and which may be arranged 
adjacent the main flow line. In this preferred embodiment, the vacuum 
valve means may be arranged between the fixed lateral flow line and the 
flexible hose. 
The flexible hose may be removably connected with respect to the sewage 
holding tank. In another preferred embodiment, the flexible hose may also 
be removably connected with respect to a vacuum valve arranged between the 
flexible hose and the fixed lateral flow line which is connected directly 
to the main flow line. 
As used herein, the term ambient air is considered to be atmospheric air 
which is present outside of the main and lateral pipelines. Thus, when the 
air inlet valve means are placed in an open position, atmospheric air is 
drawn from the outside environment into the main pipeline. It should also 
be appreciated that the term wastewater is considered to comprise various 
liquids including industrial wastewater, storm water, industrial process 
liquids as well as sewage wastewater. 
Preferably, the vacuum sewer system comprises a plurality of sewage holding 
tanks and a plurality of lateral flow lines connected to respective ones 
of the plurality of sewage holding tanks. Each of the plurality of lateral 
flow lines is connected to a main pipeline. 
The vacuum sewer system also preferably comprises a collection tank 
arranged downstream of the main pipeline which is adapted to receive the 
wastewater evacuated from the sewage holding tank. The collection tank may 
be operated in conjunction with the vacuum generating means, which may 
comprise at least one vacuum pump, so that the vacuum environment is 
between about 200 mm Hg and 600 mm Hg. 
It is preferable for the vacuum valve means to comprise a solenoid in 
combination with a valve member, such as a pinch valve, check valve, ball 
valve or the like. The solenoid is operatively connected to the valve 
member and is responsible for actuating the valve member to a desired open 
and closed position. Each of the plurality of air inlet valve means may 
comprise a solenoid valve or other electrically, hydraulically or 
pneumatically operated valve member. 
The vacuum sewer system of the present invention preferably includes 
controller means for controlling actuation of the vacuum valve means 
between the open and closed position. The controller means may comprise a 
PLC which is adapted to send control logic signals to the vacuum valve 
means. The controller means may also be used to control actuation of the 
plurality of air inlet valve means between the desired open and closed 
positions. 
It is also preferable for the vacuum sewer system to comprise a plurality 
of initial storage tanks and a plurality of corresponding gravity lateral 
lines wherein each of the gravity lateral lines has a first end connected 
to corresponding ones of the initial storage tanks and a second end 
connected to the sewage holding tank. In this embodiment, the vacuum valve 
means serves as an interface between a gravity system and a vacuum sewer 
system. 
The main pipeline may have an inner diameter of between about three inches 
and twelve inches. The lateral flow line may have an inner diameter of 
between about one inch and four inches. In alternate embodiments, the 
dimensions of the main pipeline and the lateral sewage flow lines may vary 
to accommodate desired amounts of sewage flow. 
The main pipeline of the present vacuum sewer system is preferably arranged 
in a saw-tooth pattern. Further, at least a portion of the main sewage 
flow line may be arranged below ground and preferably slopes from the 
sewage holding tank to a collection station except for vertical portions 
of the saw-tooth pattern. 
The period of time that the vacuum valve means is arranged in an open 
position may vary depending upon the amount of wastewater within an 
associated sewage holding tank and the type of vacuum sewer system used. 
In accordance with one embodiment, such as a particular vacuum sewer 
system that may be used in connection with emptying sewage holding tanks 
from railcars, an operator may manually determine the amount of wastewater 
left within a sewage holding tank. In this embodiment, the operator 
manually determines how much wastewater remains to be emptied from an 
associated sewage holding tank and then effects opening and/or closing of 
an associated vacuum valve. 
In another preferred embodiment, the period of time that the vacuum valve 
is open may be automatically calculated by a PLC. In another preferred 
embodiment, the period of time that a vacuum valve remains open or closed 
may be automatically determined by a level detection device, which may 
work in conjunction with a PLC or independent of a PLC, which causes 
opening of an associated vacuum valve when wastewater within a holding 
tank reaches a predetermined high level and automatically causes closing 
of the associated vacuum valve when the wastewater in the holding tank 
reaches a predetermined low level. 
Accordingly, it is an object of the present invention to provide a vacuum 
sewer system which includes vacuum valve means arranged between a sewage 
holding tank and a main pipeline which may be opened for a period of time 
so that substantially only wastewater is permitted to flow from the 
holding tank into the main pipeline. 
It is another object of the present invention to provide a vacuum sewer 
system which includes a plurality of air inlet valve means arranged at 
spaced locations along a main pipeline so that ambient air may be 
selectively drawn therein to increase the volume of wastewater flow in a 
given time period within one or more associated lateral flow lines. 
It is another object of the present invention to provide a novel method of 
operating a vacuum sewer system which will permit a substantially greater 
volume of sewage to flow through associated lateral flow lines in a given 
time period than has heretofore been achieved. 
These objects and other objects and features of the present vacuum sewer 
system and method of operating a vacuum sewer system will be more apparent 
after considering the following detailed description of the preferred 
embodiments in conjunction with the drawings which form part of the 
disclosed invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A vacuum sewer system in accordance with the present invention is 
schematically shown in FIG. 1 in combination with a gravity-fed sewer 
system which may be used in commercial or residential environments. FIG. 1 
particularly illustrates the present vacuum sewer system as it may be used 
to empty rail cars. However, it should be appreciated that the present 
vacuum sewer system may be used in various applications for removing 
sewage from restaurants, factories, office buildings, schools, residential 
homes, etc. 
A plurality of rail cars are identified by reference numerals 10A-D in FIG. 
1. Each of the rail cars 10A-D include a conventional gravity sewage 
system including a toilet 12A-D, a gravity-fed lateral flow line 14A-D and 
a storage tank 16A-D. The gravity-fed lateral flow lines are connected 
between the toilets 12A-D and the storage tank 16A-D. These gravity sewer 
system components are well known in the art. 
The present invention includes at least one vacuum interface valve 18A-D, 
which serves as an interface between a conventional gravity-fed system, 
and a novel vacuum sewer system. The vacuum interface valves 18A-D are 
associated with each of the storage tanks 16A-D. The vacuum interface 
valves 18A-D may be selectively actuated between an open and closed 
position by a corresponding solenoid 19A-D. In a preferred embodiment, the 
vacuum interface valves 18A-D may be pinch valves and the overall valve 
assembly includes a combination of the pinch valves and the corresponding 
solenoids 19A-D. It should be appreciated that in alternate embodiments a 
single unit solenoid valve or other valve assemblies may be used in place 
of the composite pinch valve and solenoid arrangement. 
Manual valves 15A-D are arranged on the holding tanks 16A-D along with 
quick disconnect couplings (not shown) for connecting associated lateral 
flow lines to the holding tanks 16A-D. In a preferred embodiment, such as 
an embodiment used to remove wastewater from sewage holding tanks on 
railcars, the lateral flow lines may comprise multiple components such as 
selectively removable flexible hose portions 17A-D and fixed substantially 
rigid components 24A-D which are directly connected to the main sewer 
pipeline 30. The flexible hoses 17A-D have a first end which may be 
connected to quick disconnect couplings at the manual valves 15A-D of the 
holding tanks 16A-D. A second end of the flexible hoses 17A-D is arranged 
downstream of the first end and may be connected to the upstream end 20A-D 
of the vacuum interface valves 18A-D as shown in FIG. 1. A downstream end 
22A-D of the vacuum interface valves 18A-D is spaced from the upstream end 
20A-D. It should be appreciated that the distance between the upstream and 
downstream ends of the vacuum interface valves may be a very small 
distance. The distinction between the upstream and downstream end has been 
made to more particularly define the portions of the vacuum interface 
valve 18A-D that are closest to the sewage holding tank 18A-D and the 
associated fixed lateral flow lines. 
Although various types of vacuum interface valves may be used in accordance 
with the present invention, an air-operated pinch valve has proven 
reliability in vacuum service. This valve may have a straight-through full 
bore which is ideal for undiluted toilet waste service. When coupled with 
the solenoids 19A-D, the vacuum interface valves 18A-D function as an 
electrically operated vacuum valve which is reliable and simple to 
maintain. 
As shown in FIG. 1, fixed lateral flow lines 24A-D are provided and have an 
upstream end 26A-D connected to the downstream end 22A-D of corresponding 
vacuum interface valves 18A-D. The fixed lateral flow lines 24A-D also 
have a downstream end 28A-D which is secured to a main pipeline 30. It is 
preferable for the lateral flow lines 24A-D to be made of a substantially 
rigid material, such as schedule 40 PVC (polyvinylchloride) PVC pipe. 
The particular dimensions, including the length and inner diameter of the 
fixed lateral flow lines 24A-D, may vary in alternate embodiments. In a 
preferred embodiment, the fixed lateral flow lines 24A-D may have an inner 
diameter of between about two inches and four inches. However, in 
alternate embodiments, larger or small diameter flow lines may be used. 
Similarly, the flexible lateral flow lines 17A-D preferably have an inner 
diameter of between about two inches and four inches, but may have a 
larger or smaller diameters depending upon the particular application for 
which they are used. 
Couplings (not shown) may be used to connect an upstream end of the fixed 
lateral flow lines 24A-D between the vacuum interface valves 18A-D and the 
main sewer pipeline 30. The couplings should have a structure which is 
sufficient to operate in a vacuum environment of between about 200 mm Hg 
and 600 mm Hg. 
It is preferable for the lateral flow lines 17A-D to be made of a 
substantially flexible hose-like material so that emptying of the sewage 
holding tanks 16A-D of the railcars 10A-D may be performed when the 
railcars 10A-D are in various positions with respect to the coupling areas 
of the vacuum interface valves 18A-D and the fixed lateral flow lines 
24A-D. 
As illustrated in FIG. 1, the main sewer pipeline 30 may have a saw-tooth 
profile. This is a hydraulically efficient profile as it enhances the flow 
rate of wastewater through the main pipeline 30 and it permits the main 
pipeline 30 to remain shallow beneath the ground surface. It is preferable 
for the main pipeline 30 to have an overall slope toward a central vacuum 
collection station. This slope may vary depending upon the environment. 
However, it has been found that an overall slope of at least two feet per 
1000 feet of pipeline is preferable. 
The main pipeline 30 may be constructed of various corrosion-resistant 
materials. In a preferred embodiment, the main pipeline 30 is a PVC pipe 
which has an inner diameter of between about four inches and twelve 
inches. It should be understood that the inner diameter of the PVC pipe 
may vary in particular applications and thus may be smaller or larger than 
the aforementioned dimensions. 
A plurality of air inlet valves 32A-H are connected at spaced distances 
along the main sewer pipeline 30. Each of the air inlet valves 32A-H may 
be a solenoid operated valve member that can be selectively moved between 
the open and closed positions. The distance between the air inlet valves 
is preferably no more than about 1000 linear feet and may be less than 
about 200 linear feet. However, in alternate embodiments, the distance 
between the closest ones of the air inlet valves 32A-H may be greater than 
1000 linear feet or substantially less than 200 linear feet. 
The main sewer pipeline 30 is connected to a collection tank 38 which may 
be arranged at a vacuum station. A vacuum pump 40 is operatively 
associated with the collection tank 38 and the main pipeline 30. The 
vacuum pump may be an oil-cooled continuous-run rotary vane type pump 
which has been proven to be reliable in vacuum sewer applications. 
Alternatively, various other types of vacuum pumps may be used within the 
scope of the present invention. The vacuum pump 40 should be sufficient to 
create a vacuum environment of at least between about 200 mm Hg and 600 mm 
Hg with the main pipeline 30 and the associated lateral lines 24A-D. 
A sewage pump 42 is connected to the collection tank 38 for pumping sewage 
from the collection tank 38 to a transport truck or a sewage treatment 
plant. Various types of sewage pumps may be used in accordance with the 
present invention. One conventional sewage pump which has been 
successfully used is a centrifugal pump which is typically used in 
submersible sewage lift stations and dry-pit applications and has net 
positive suction head characteristics suitable for vacuum sewer systems. 
As schematically illustrated in FIG. 1, a PLC 36 may be connected to 
various components of the present vacuum sewer system to obtain control 
over the system. The PLC must be capable of controlling repetitive on-off 
sequencing operations. One commercially available PLC which is suitable 
for use with the present vacuum sewer system is the Allen Bradley 5/25 
PLC. 
As illustrated in FIG. 1, the PLC is coupled to the solenoids 19A-D for 
controlling the vacuum interface valves 18A-D, the air inlet solenoid 
valves 32A-H, the vacuum pump 40 and the sewage pump 42. In alternate 
embodiments, separate PLC's may be used to control various features of the 
present vacuum sewer system. However, in the preferred embodiment shown in 
FIG. 1, a single PLC controls the wastewater level in the system, the rate 
of sewage flow through the lateral flow lines 17A-D and 24A-D and the main 
flow line 30, and removal of wastewater from the collection tank 38. 
Level detection devices 13A-D may be operatively associated with the sewage 
holding tanks 16A-D to detect high and low wastewater levels and to 
generate signals in response to such levels so that the associated vacuum 
interface valves 18A-D can open and close based on the level of wastewater 
within the sewage holding tanks 16A-D. The level detection devices 13A-D 
may operate on a float principal, a pneumatic principal such as a bubbler 
system, an ultrasonic principal or other level detection principles which 
are generally known in the art. The level detection devices 13A-D may 
operate in conjunction with the PLC 36 or may operate independent of the 
PLC 36. 
In an embodiment where a PLC is not required, the level detection devices 
13A-D may operate independent of a timer for effecting opening and closing 
of associated vacuum interface valves 18A-D. In such a vacuum sewer 
system, wastewater may flow substantially continuously from the holding 
tanks 16A-D provided that the level of wastewater which flows into the 
holding tanks 16A-D does not drop below a predetermined level. Such a 
vacuum sewer system may require handling of large amounts of wastewater. 
In another embodiment, such as the emptying of railcars, it may desirable 
to limit the sewage flow with the vacuum sewer system. In this type of 
environment, it would be desirable to use a PLC to control the opening and 
closing of the vacuum interface valves 18A-D at timed intervals so that 
the vacuum interface valves would be considered throttled. For instance, 
it may be desirable to limit wastewater flow to 100 GPM. Throttling of the 
vacuum interface valves 18A-D may be preprogrammed in the associated PLC 
36 so that the wastewater flow rate will never be permitted to exceed 
about 100 GPM. 
One important aspect of the present invention pertains to actuation of the 
vacuum interface valves 18A-D which are designed to cycle in accordance 
with control logic signals sent by the PLC so that substantially only 
wastewater is drawn out of the storage tanks 16A-D. This is different from 
prior art vacuum interface valves which were generally designed to operate 
by allowing liquid sewage to be admitted from a storage tank to a lateral 
flow line for a predetermined period of time and then permitting a supply 
of air to be drawn into the associated flow lines. Various air to liquid 
ratios were required when using prior art vacuum interface valves. The 
prior art systems which used these two-phase vacuum interface valves were 
not as efficient as the present vacuum sewer system because the air 
admitted into the associated lateral lines displaced a certain amount of 
wastewater, thus limiting the amount of wastewater that could flow through 
the lateral lines at a given time. Such prior art systems usually obtained 
overall flow rates of less than about 15 gallons per minute (GPM) of 
liquid sewage for each vacuum valve used in conjunction with the lateral 
lines. Although the prior art systems perform satisfactorily in 
environments where relatively low flow applications are needed, they are 
not fully capable of meeting the demand of high flow environments unless a 
large number of vacuum valves are utilized. 
By using vacuum interface valves 18A-D, which do not permit any appreciable 
amount of air to flow into the associated lateral lines 24A-D, in 
conjunction with the air inlet valves 32A-H, the flow rate of wastewater 
through the lateral lines 24A-D can be increased to well over 100 GPM and 
may reach in excess of 200 GPM. This advantageous aspect of the present 
invention will be discussed further below in connection with the operation 
of the present vacuum sewer system. 
When operating the present vacuum sewer system in accordance with the 
present invention, an operator may be required to manually connect a first 
end of a flexible lateral flow line, such as lateral lines 17A-D, to the 
quick disconnect coupling (not shown) at the manual valves 15A-D of the 
sewage holding tanks 16A-D. A second end of the flexible lateral lines 
17A-D would be connected to the upstream end 20A-D of the vacuum interface 
valves 18A-D. The downstream end 22A-D of the vacuum interface valves 
18A-D is arranged adjacent the upstream end 26A-D of the fixed lateral 
flow lines 24A-D, which is fixed at the downstream end 28A-D to the main 
line 30. 
A flow chart depicting operation of the vacuum sewer system in accordance 
with the present method is shown in FIG. 3. It should be appreciated that 
the step of connecting the flexible lateral flow lines 17A-D between the 
sewage holding tanks 16A-D and the vacuum interface valves 18A-D may not 
be necessary in environments where the lateral flow lines 24A-D and the 
vacuum interface valves 18A-D are already connected between associated 
sewage holding tanks 16A-D and the main flow line 30, such as in 
environments wherein the sewage holding tanks 16A-D are not mobile. 
Prior to connection of the flexible lateral flow lines 17A-D in assembled 
position, an operator may be required to push an initial activation button 
(not shown) which has the effect of activating the PLC 36 to operate the 
timing for all of the sewer interface valves 18A-D and the air inlet 
valves 32A-H. To this end, the PLC 36 sends control signals to the 
associated solenoids 19A-D of the vacuum interface valves 18A-D and the 
air inlet solenoid valves 32A-H. The PLC 36 may also simultaneously send a 
signal to the vacuum pump 40 which will activate the vacuum pump to create 
a predetermined vacuum environment within the main flow line 30 and the 
associated lateral flow lines 24A-D. As indicated above, this vacuum 
environment is preferably between about 200 mm Hg and 600 mm Hg. 
For simplification purposes, the vacuum pump 40 is described as comprising 
a single vacuum pump. However, in actual operation, the vacuum pump 40 may 
comprise a lead vacuum pump and one or more secondary vacuum pumps. It may 
take several or more minutes for the vacuum pump 40 to obtain the desired 
vacuum environment within the main pipeline 30 and the lateral flow lines 
24A-D. Once the desired vacuum environment has been obtained, and after 
the flexible lateral flow lines 17A-D have been connected into assembled 
position, cycling of the vacuum valves 18A-D and the air inlet valves 
32A-H will commence. 
A simplified view of the relationship between an air inlet solenoid valve 
32A and the main sewer pipeline 30 is shown in FIG. 2. Although FIG. 1 
depicts eight inlet air valves 32A-H spaced along the main sewer pipeline 
30, it should be appreciated that the quantity of air inlet valves may 
vary depending upon the desired volume per unit time flow rate of 
wastewater within the lateral flow lines 24A-D. Since the vacuum interface 
valves 18A-D do not allow any appreciable amount of air to flow into the 
lateral flow lines 24A-D, the air inlet valves 32A-H are used to draw 
ambient air from the outside environment directly into the main sewer 
pipeline 30 while substantially only sewage is drawn into the main 
pipeline 30 through lateral flow lines 17A-D and 24 A-D. Each of the air 
inlet solenoid valves 32A-H are independently operated and controlled by 
the PLC. It has been found that it is advantageous to draw air into the 
main pipeline 30, as opposed to the lateral flow lines 24A-D because the 
main pipeline 30 has a larger inner diameter and thus, the ambient air 
drawn therein does not displace wastewater in the same way that it would 
within the lateral flow lines 24A-D. 
The manual valves 15A-D are normally arranged in a closed position. These 
valves may be opened after the flexible lateral flow lines 17A-D are 
connected between the sewage holding tanks 16A-D and the upstream end 
20A-D of the vacuum interface valves 18A-D. The gravity system components 
including the toilets 12A-D, the gravity lateral flow lines 14A-D and the 
sewage holding tanks 16A-D are thus isolated from the vacuum sewer system 
components including the lateral flow lines 24A-D, the main pipeline 30, 
the collection tank 38 and the vacuum pump 40. The frequency and the 
duration of time that the vacuum interface valves 18A-D are placed in an 
open position may vary depending on the physical location of the valves 
within the system. Thus, the open frequency and duration of the vacuum 
interface valves 18A-D are preferably individually adjustable between 0.1 
seconds and about 10 minutes. Of course, the vacuum interface valves 18A-D 
can remain open for substantially longer periods of time in particularly 
high flow environments where continuous flow applications are required. 
The frequency parameters can be programmed into the PLC 36. An initial 
cycling period for the vacuum interface valves 18A-D may be 30 seconds 
open followed by 5 seconds closed for a total cycle period of 35 seconds. 
This will allow "slugs" of wastewater (a combination of liquid and solid 
sewage with water or other chemical-based liquid used to facilitate 
removal of the sewage) to flow from the holding tanks 16A-B through the 
flexible lateral lines 17A-D and the vacuum interface valves 18A-D and 
into the fixed lateral vacuum flow lines 24A-D. FIG. 4 illustrates a block 
diagram depicting the wastewater flow from the gravity system plumbing 
components through the vacuum interface valves 18A-D and into the vacuum 
system components. 
When the vacuum interface valves 18A-D are activated by the PLC controlled 
solenoids 19A-D to an open position, the vacuum environment, which is the 
difference between the barometric pressure and the vacuum pressure created 
by the vacuum pump 40, draws wastewater from the storage tanks 16A-D into 
the lateral flow lines 17A-D and 24A-D. A sewage slug is then formed and 
is drawn into the main pipeline 30 where it passes the air inlet valves 
32A-H. Cycling of the air inlet valves 32A-H has been commenced by the 
control signals sent by the PLC 36. The air inlet valves 32A-H are 
normally arranged in a closed position so that the vacuum environment 
created by the vacuum pump 40 within the main pipe line 30 is isolated 
from the outside environment. The open frequency and duration of the air 
inlet valves 32A-H is preferably individually adjustable between about 0.1 
seconds and 60 seconds. If desired, the air inlet valves 32A-H can remain 
open for shorter or longer periods of time. This frequency time period can 
be programmed into the PLC 36 to allow for adjustments in the frequency 
and duration of the open position. A typical cycle of the air inlet valves 
32A-H may be 5 seconds open followed by 25 seconds closed for a total 
cycle period of 30 seconds. Air is drawn in from the outside environment 
during the period of time that the air inlet valves 32A-H are in an open 
position to increase the volume per unit time of wastewater flowing within 
the lateral flow lines 24A-D. 
The vacuum pump 40 evacuates air from the collection tank 38, the main 
pipeline 30 and the vacuum lateral lines 24A-D so that a pressure 
differential exists and the internal vacuum pressure is at a lower 
absolute pressure than the atmospheric pressure which exists in the 
ambient environment. This pressure differential creates a hydraulic energy 
gradient from the storage tanks 16A-D towards the collection tank 38 upon 
opening of the manual valves 15A-D and the vacuum interface valves 18A-D. 
This drives the wastewater which is drawn into the flexible and fixed 
lateral flow lines 17A-D and 24A-D toward the collection tank 38. The air 
which is drawn in from the ambient environment through the air inlet 
valves 32A-H greatly increases the volume per unit time of wastewater 
flowing through the lateral lines 24A-D. To this end, wastewater admitted 
into the lateral flow lines 24A-D can be forced to flow at rates 
substantially greater than 100 GPM. This is a remarkable increase over 
prior art systems which obtain flow rates of up to about 15 GPM when a 
similar number of vacuum interface valves are used. 
As the wastewater is continuously drawn towards the collection tank 38, it 
may be completely evacuated from the storage tanks 16A-D. When the level 
of wastewater drawn into the collection tank 38 exceeds a predetermined 
level, the PLC 36 or associated level detection devices 13A-D will actuate 
the associated sewer pump 42 so the sewage within the collection tank 38 
will be pumped into a sewage truck for transportation to a treatment 
plant, or may be transported into an associated pipeline for direct 
pumping to a sewage treatment plant. 
After completing the method for removing the wastewater from storage tanks 
16A-D, the operator can either manually shut off the power to the 
associated vacuum sewer system or the PLC may be programmed to detect 
completion of the sewage transport operations so that power to the system 
is automatically shut off. In the rail car embodiment shown in FIG. 1, the 
operator should then disconnect the flexible lateral lines 17A-D from the 
quick disconnect coupling at the sewage holding tanks 15A-D, the vacuum 
valves 18A-D, or both. 
The foregoing description and figures of the present invention are directed 
toward a preferred embodiment of the present vacuum sewer system and a 
method of operating the same. It should be appreciated that various 
modifications can be made to each of the components of the present vacuum 
sewer system and the steps of operating the system. Indeed, such 
modifications are encouraged to be made in the materials, dimensions, 
structure of the disclosed embodiments of the present invention, as well 
as modifications in the particular order and nature of the steps of the 
method, without departing from the spirit and scope thereof. Thus, the 
foregoing description of the preferred embodiments and methods should be 
taken by way of illustration rather than by way of limitation.