Note: Descriptions are shown in the official language in which they were submitted.
CA 02209661 2005-12-22
TITLE
Waste Tank for Vacuum Sewage System
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Background of the invention
This invention relates to a waste tank for a
vacuum sewage system used in conjunction with aircraft
vacuum toilet systems.
As disclosed in U.S. Patent No. 5,026,407, anyone
who has ever made a relatively long flight aboard a
commercial passenger jet is probably familiar with their
toilets. Flushing these devices results in toilet fluids
and solid wastes being drawn from a toilet bowl down a
waste line. Unlike conventional toilets, where waste
exits the toilet bowl via a circular water flow that
carries the waste through a bottom outlet, the toilets in
the most recent passenger jet models are vacuum toilets
that rely upon suction for removing waste. This creates
the familiar sucking sound that accompanies flushing this
particular toilet. A common attribute of such systems is
that a flushing airflow is created by venting toilets
externally of the aircraft. This is accomplished by
opening a valve, which creates an airflow path from a
given toilet bowl to the outside or ambient atmosphere via
a waste line and tank system. The pressure differential
between the toilet cabin and the outside is what actually
generates the airflow. At certain low elevations,'where
the pressure differential is not great, a vacuum blower is
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employed to assist or augment the natural pressure
differential between inside and outside the aircraft.
Of course, the solid and liquid waste in the
toilet is not simply dumped outside the aircraft.
Instead, it is separated from the airflow, and deposited
in a waste tank prior to venting the air overboard.
Typically, the airflow and entrained waste travel
from the toilet to the waste tank via conventional pipes
or lines. The conventional waste tank has one or more
waste inlets configured to direct the flow
circumferentially in a clockwise direction around the
tank's interior, but at a level that is above and parallel
to the level of waste already in the tank. As a result, a
combination of centrifugal forces and gravity cause
separation of much of the entrained matter from the
airflow, and it simply drops downwardly into the tank.
Some entrained matter remains with the airflow and is
removed via a separator as it exits the tank. This device
is normally positioned inside the top portion of the tank.
However, when the tank reaches a level approaching
the full liquid level of the tank, the kinetic energy of
the sewage entering the tank causes splashing and creates
waves which interact with the airflow causing more liquid
to be entrained in the airflow than can be handled
efficiently by the separator. In this case liquid is
exhausted to the atmosphere and forms ice on the aircraft
exterior which then could break off and cause serious
problems when it strikes the ground.
The waste tank system described above has sensors
for detecting the level of waste inside the tank. These
sensors have faces that are positioned at a certain
vertical height along the tank's inner wall, and provide
an electrical signal indicating a full tank in response to
contact with the waste as its level rises. In the full 35 tank condition, the
level sensors remove power from all
toilets connected to the tank.
The above-described tank inlet arrangement, which
a circular flow motion inside the tank, also creates a
problem in that it tends to coat the waste level sensor
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faces with solid and liquid waste. This has been known to
cause the sensors to emit signals falsely indicating a
full tank, resulting in unnecessary shutdown of the
toilet. This naturally results in a serious inconvenience
for the passengers.
The typical waste tank system also has one or more
rinse nozzles that protrude into the tank. These are
connectable to an external source of clean water for
periodically rinsing and/or cleaning the tank during
aircraft maintenance intervals. They also tend to be
coated by incoming waste from tank inlets which can clog
them.
Summary of the Invention
A waste tank for a vacuum sewage system according
to this invention is defined by a tank having a continuous
sidewall, a top, a bottom, an inlet for admitting air and
sewage tangentially into the tank, and an outlet for
exhausting air separated from liquid from the top of the
tank. The inlet and outlet are above the maximum liquid
filling level in the tank, and a shelf is attached to and
extends from the interior surface of the sidewall of the
tank and is located above said filling level and below
said inlet whereby interaction between air being admitted
through said inlet and the liquid in the tank is reduced.
The shelf extends partially around the sidewall of
the tank and is directed upwardly from said inlet.
The waste tank includes a rotary spray nozzle
centrally mounted to said top of said tank through which
spray liquid is forced and which rotates by the reactive
force of the liquid spray ejected from the nozzle, the
nozzle being directed toward said sidewalls.
The tank is formed of a filament wound graphite
- ribbed structure impregnated with epoxy resin and has an
abrasion resistant fluorocarbon polymer coating on its
inside surfaces.
The waste tank also includes a frame and means for
externally supporting said tank from said frame and
sensing the weight of said tank.
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Brief Descrigtion of the Drawinc7s
Fig. 1 is a perspective view of the waste tank of
this invention.
Fig. 2 is a side elevation view partially in cross
section of a waste tank showing the tank connected to a
toilet bowl.
Fig. 3 is a transverse cross section of the tank
of Fig. 2 taken along lines 3-3.
Detailed Descritotion of the Preferred Embodiment
The embodiment chosen for purposes of illustration
as shown in the drawings includes a waste tank generally
designated 10 with inlets 142 and 1412, a separator 12, and
a weight sensing system 16 supporting waste tank 10 on a
frame 18.
The tank 10 is a filament wound, graphite epoxy,
autoclaved cured structure. The curing method creates a
low void structure allowing the tank wall to be the
containment barrier preventing liquid penetration through
the tank wall.
There is a coating on the inside of the tank of an
abrasion resistant impregnated fluorocarbon resin
material. The abrasion resistant material prevents damage
to the tank wall when various solid materials enter the
tank with waste. The fluorocarbon resin aids in cleaning
when the inside of the tank is flushed with clean water.
This also reduces the tendency of debris to stick to the
walls of the tank.
The tank has integrally wound ribs 11. Since the
system works on vacuum, the ribs increase the buckling
resistance of the tank at a minimum weight penalty. Also
the graphite epoxy structure is designed to work at a very
low stress level yielding excellent fatigue life.
As best shown in Figs. 2 and 3, the vacuum waste
system includes a toilet 20 connected to the tangential
inlet 14.a of tank 10 by a waste line 22. The toilet is
flushed by opening valve 19 at the bottom of the toilet
bowl which creates an air flow passage from the toilet 20
to a vent outlet 24. Solid and liquid waste inside the
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toilet is drawn through the waste line 22 into tank 10 by
the pressure differential between the aircraft cabin and
the pressure outside the aircraft. The system may be
provided with a blower (not shown) that assists the
creation of an airflow at lower elevations where there is
not much difference between cabin pressure and pressure
outside the aircraft.
A separator device 12 is shown mounted to the top
of tank 10 above the full liquid level of the tank. The
separator includes dual filters 12a and 12b and
incorporates through passages from air intake inlet 13 of
the separator to outlet or vent 24. A skirt 12c isolates
inlet 13 from the drain area 15 of the separator which
reduces the possibility of any separated drainage liquid
being picked up by the inlet air and being recycled
through the separator.
A rotary spray cleaning nozzle 26 is centrally
mounted to the top of the tank and is connected to
pressurized liquid source through passage 28 through which
spray liquid is forced from a source not shown. The spray
nozzle is rotated by the reactive force of the liquid
spray ejected from nozzle which allows the interior of the
tank 10 to be cleaned because the interior surface of the
tank is subject to the liquid spray.
A pair of shelves, shelf 30 and 31, are attached to
the interior of sidewall 32 of tank 10 and extend into the
tank from the sidewall. The shelves are located above the
maximum filling level of the tank and below the tangential
inlets 14a and 1412 of the tank. Inlet 14a interacts with
shelf 30 and inlet 1412 interacts with shelf 31. Each
shelf extends partially around the sidewall and is
directed upwardly at an angle A from a horizontal line 33.
Angle A is preferably 5 degrees.
In operation, as shown in Fig. 2, the air and
sewage enters through tangential inlet 14.a into tank 10
and falls to shelf 30 which provides the initial
separation of liquid and solids from the air, i.e. the
liquid and solids flow off the shelf into the tank and the
air with some entrained moisture is directed upwardly to
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the separator inlet 13 of separator 12 and does not
interact with the liquid in the tank. Inlet 1412 interacts
with shelf 31 in a similar manner.
The weight sensing system incorporates three 5,000
pound load cells 16 (Sensotec model 31) supporting waste
tank 10 from frame 18. Thus the sensing system is located
externally to the tank.
The output of the load cells after conditioning
goes through a microprocessor 17 to a readout. The
microprocessor not only integrates and averages the
weight, it tares out any acceleration effect from the
system accelometer. The system will read the percentage
full at remote locations and at the emptying station.
This will allow a check before use. The design will tare
the system weight so any weight build up in the tank will
be shown on the readout of the microprocessor.
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