Note: Descriptions are shown in the official language in which they were submitted.
VACUUM SEWER ARRANGEMENT
Background of the Invention
The invention relates to a vacuum sewer
arrangement.
In a vacuum sewer arrangement, a toilet bowl
is connected to a sewer by means of a sewer valve,
and a vacuum is maintained in -the sewer. In order
to carry out a flushing operation, the sewer valve
is opened and waste in the toilet bowl is inducted
into the sewer. The flushing operation includes
the following phases:
a) rinse water is introduced to flush the
inside of the toilet bowl and the sewer valve opens,
b) the waste in the bowl is pressed into the
sewer by the pressure difference between the toilet
bowl and -the sewer
a) air enters the sewer behind the waste, and
d) the sewer valve closes.
The waste forms a movable plug in the vacuum
sewer, and the pressure difference across the
plug propels the plug through the sewer to a waste
receiving tank. Tn a conventional vacuum sewer
arrangement, air for transportation of the waste plug
enters the sewer by way of the sewer valve. when the
sewer valve oloses, the plug stops moving almost
immediately.
Two main factors determine how long the sewer
valve remains open. First, the sewer valve must
remain open for long enough to ensure, with a
reasonable degree of certainty, that the waste in the
toilet bowl has entered the sewer. Although normally
the waste is pressed into the sewer almost instan-
taneously, it is usual to allow about two
secands for the waste to enter the sewer. Second,
it is important for proper operation of a vacuum
sewer arrangement that the chance of a waste plug
merging with a preceding or succeeding plug in the
sewer be very small, and therefore it must travel a .
substantial distance along the sewer, for example at
least 10 m, before stopping. In vacuum sewer
arrangements that are currently in use, the waste
plug typically travels at a maximum speed of about
5-10 m/s. Therefore, in a typical vacuum sewer
arrangement, the sewer valve remains open for abaut
four seconds on each flush.
The waste will enter the sewer immediately the
sewer valve opens, followed by a large quantity of
air. This pauses considerable pressure variations
in the toilet bowl, in particular during the opening
and closing phase of the sewer salve when material
(waste or air) is inducted through a relatively small
opening. Due to this, a high noi~~ level is
generated. The noise level is dependent on
the pressure difference beicween the toilet bowl
and the sewer - the greater the difference, the
greater the noise.
The Patent Publication GB-A-2203461 discloses
a vacuum sewer arrangement with a noise reducing air
inlet device connected to the sewer immediately
downstream of the sewer valve.
Summary of the Invention
The object of the invention is to provide a
simplified and more reliable versi~n of tha arrange-
meat disclosed in GB-A-2203461.
A disadvantage of the vacuum sewer arrangement
described with reference to Figure 1 in GB-A-2203461
is that a vacuum accumulator may be required in order
to provide a sufficiently large volume under vacuum
for proper functioning of the sewer valve and the air
inlet valve. Also, since the air inlet valve opens
after the sewer valve, and a single control device
is used to contral both the sewer valve and the air
inlet valve, a throttle is required in order to delay
operation of the air inlet valve relative to the~sewer
valve. Further, the proper location of the outlet
of the air inlet duct depends on several factors,
and i~t is not possible to be certain that these
factors will remain constant or will be 'the same from
installation to installation.
According to the invention a much simpler and
more reliable system is obtained by applying means
for operating the air inlet valve in response to the
pressure in the vacuum sewer close to the sewer
valve, as stated in claim 1.
The air inlet duct can be made sound insulated
and can be provided with a muffler. Then air
flowing through the air inlet duct will not cause a
disturbing level of noise. The noise level of a
vacuum toilet sewer arrangement according to the
invention cars be further reduced by providing as know
.her se, the toilet bowl with a lid forming a substan-
tially airtight and sound--proof closure at the top
of the bowl. In this oa~e, it is favorable that the
lid be of r~lativeiy think sound insulating material.
Various plastic materials, sandwich structures etc.
are well suited for this purpose. If the lid provi-
des a seal, the volume of air contained in the bowl
may be too small for proper discharge of the sec~age
from the bowl, in which case additional air can
be provided -through a separate tube. This tube may
have its inlet end connected to the air a.nlet duet
upstream of the air inlet valve; but it may also b~
a completely separate tube. The lowest noise level
is achieved if the tube is provided with a muffler,
is sound insulated and has its inlet end outside the
toilet compartment. The tube is preferably provided
with a non-return valve in order to prevent escape
of odours from the toilet bowl into the surroundings.
The connection of the air inlet duct to the
sewer is sufficiently close to the sewer valve that
l~
in narmal operation of the vacuum sewer arrangement,
the sewage plug formed when the waste enters -the sewer
through the sewer valve will pass the outlet of the
air inlet duct :Less than one second after the sewer
valve reaches its fully open condition, and preferably
less than 0.5 seconds after the sewer valve reaches
its fully open condition. The air inlet valve opens
less than 2.5 seconds after the sewer valve opens,
and preferably between 1 and 2 seconds after the sewer
valve opens; and most preferably about 1.5 seconds
after the sewer valve opens. However, the time at
which the air inlet valve opens must be Selected
relative to the distance between the sewer valve and
the outlet of the air inlet duct and the expected
speed of travel of the sewage plug so that the air
inlet valve will not open before 'the sewage plug has
passed the air inlet duct, since otherwise proper
-transportation of the plug might not be aetaieved.
The air inlet valve stays open for about 5 seconds
ox less. This introduces s:Lightly more transport air
into the sewer than what is usual in conventional
vacuum sewer systems. The increased amount of air
provides a longer travel dlistance for the sewage
plug.
Conventionally, the sewer valve of a vacuum
sewer arrangement is operated by using the vacuum
present in the vacuum sewer. Zn an ax°rangement
according to the. invention the same vacuum can be used
also for operating the air inlet valve. This gives
a simple and reliable structure.
A check valve should be arranged between the
sewer valve control device and the sewer, so that a
pressure rise in the sewer is unable to have any
influence on the pressure in the valve control device.
Zn this specification and in the claims the
following terminology is used. The team "vacuum" means
"partial vacuum" of a magnitude suitable far use in
a vacuum sewer system. Conventionally, the vacuum
in such a system is about ~ atmosphere, or about 38
~~~c~'8~
cm Hg. The term "atmospheric pressure" means the
pressure in areas where people may stay. Thus, in
an aircraft at high altitude "atmospheric pressure"
means the cabin pressure, which may be considerably
lower than the normal air pressure at ground level.
Brief Description of the Drawings
The invention will now be described in greater
detail with reference to the accompanying drawing,
in which
FIG. 1 schematically shows, partly at an
enlarged scale, one embodiment of the invention, and
FIG. 2 schematically shows an arrangement
according to the invention having multiple toilet
bowls.
Detailed Description
FIG. 1 illustrates a toilet bowl 1 and a
sewer pipe 2 connected to the toilet bowl by a sewer
valve assembly 3. The interior space of the sewer
2 is maintained under vacuum, which is provided, as
known per se, by a vacuum purnp (not shown). This pump
is usually connected to the downstream end of the
sewer 2, or may be eonnecte~d to a sewage collecting
tank (not shown). The sewer valve assembly 3 includes
a sewer valve proper and a sewer valve operating
device which opens the sewer valve by using
vacuum. Various valve assemblies of this type
are described in U. S. Patents Nos. 3,482,267,
3;807,431, 3,984,080 and 4,376,444. Since suitable
vacuum operated valves are known, the structure of
the sewer valve assembly will not be explained here.
An air inlet duct 4 opens into the sewer 2
through an outlet 36. An air inlet valve assembly
6 is connected to the air inlet duct 4. A control
device 7, which contrals the valve assemby 3, is
activated by a function impulse 8. Such an impulse
may originate from a push button operated by the user
of 'the toilet and may be transmitted, for instance
mechanically, in the form of a pressure impulse, or
electrically, to the control device 7. The
function impulse 8 may be dependent on, for
instance the closing of a lid 17 of the tailet bowl
ar on other factors which are relevant to
controlling the flushing of the toilet. Since
these factors also are well known in the art,
neither the creating of a function impulse nor the
manner of operation of the control device 7 will be
explained here.
A general principle in a vacuum sewer arrange-
ment is that the sewer valve should apen only when
there is sufficient vacuum in the sewer for
effective transport of sewage. In order to achieve
this, the vacuum required to open the sewer valve
is taken from the sewer 2 or from another point of
the vacuum system. If the available vacuum is too
weak for effective transport of sewage, the sewer
valve will not open. In the embodiment of FIU. 1
the vacuum required for the operation of the sewer
valve is communicated from 'the sewer 2 to the control
device 7 through a tube 9 and a check valve lp.
Upon receiving a function impulse 8; the control
device 7 transmits vacuum x~eceived from the sewer 2
through a tube 13 to the sewer valve operating device,
which then opens the sewer valve. At the same time
the control device 7 transmits vacuum through a tube
34 towards the air inlet valve assembly 6.
The distance of the outlet 36 of the air inlet
duct from the sewer valve assembly 3 and the delay
between opening of the sewer valve and opening of
the air inlet valve are selected so that, in normal
operation, the air inlet duct 4 supplies air to the
sewer soan after the sewage plug from the toilet
bowl has passed the outlet 36. Since air for
transporting the plug is then provided through the
air inlet duct, the sewer valve need not be held
open any longer than is necessary to ensure that
7
the plug has passed the outlet 3S. When the sewer
valve closes, air is no longer inducted through the
toilet bowl and the noise level is reduced. More
over, when both the sewer valve and the air inlet
valve are open, air is inducted through the sewer
valve at a lower rate and the noise level is
reduced.
The basic structure of an arrangement
according to the invention requires that air is led
through the air inlet duct 4 to the vacuum sewer 2
when the sewage providing unit 1 is to be emptied.
This substantially reduces the noise level, but
nevertheless, the noise level might be unpleasantly
high. Eience, letting in air by way of an air inlet
duct is not always sufficient to reduce the noise
level to an acceptable value. Additional measures
might be necessary for improving the technical
effect of the basic embodiment of the invention. A
suitable additional measure is to provide the
toilet bowl or the corresponding sewage providing
unit with an airtight lid 17. Such a lid should be
made relatively soundaproof. Opening of the sewer
valve can, as known .~>e-r se, easily be made depen-
dent on the olosing of the lid 17, so 'that the
valve og~ens only when the lid is closed.
Using an airtight lid in a vacuum toilet may
result in the amount of air present in the toilet
bowl 1 being too small for efficient flushing.
This can be cured by connecting an air tube 18 to
the bowl 1. Air is led into the bowl through the
tube 18 without any substantial noise. The air
supply for the tube 18 can be taken from any place,
fox instance, from outside the toilet compartment.
In the embodiment shown in FIG, 1, the air
inlet valve 6 comprises a diaphragm 30, for instance
a rubber pad, that is deflectable towards and away
from the upper end of the duct 4, depending on the
difference in pressure between the duct 4 and a
control chamber 32, which is connected by a narrow-
bore tube 34 to the tube 13. The control chamber is
bounded partially by the diaphragm 30 and partially
by a rigid wall 38, to which the diaphragm 30 is
connected through a flexible rubber skirt 42 and a
flange 44. The flexible rubber skirt 42 biases the
diaphragm 30 towards duct 4.
~lormally, the pressure in tube 13 is atmo-
spherie, while there is a lower pressure in the duct
4 because it is directly connected to the sewer 2,
which is under vacuum. As a result, the diaphragm
30 is held in firm sealing contact with the upper end
of the duct 4. On receiving a function impu7~se 8,
the cantrol unit 7 communicates vacuum from the
sewer 2 to the -tube 13. This opens the sewer valve
3, and waste in the toilet bowl is drawn rapidly
into the sewer 2.
The vacuum in tube 13 is communicated through
'the tube 34 to the control chamber 32 and
the pressures on the two sides of the diaphragm are
then equal. Hawever, owing to the bias provided by
the resilient skirt 42, arnd the difference between
the area of the diaphragm exposed to pressure in
duct 4 and the area of the diaphragm and skirt
effectively exposed to pressure in chamber 32, the
diaphragm remains in contact with -the duct 4 and
therefore the air inlet valve remains closed. When
the waste passes the outlet 36 0~ the duct 4, and
is followed by air from the toilet bowl 1, the
pressure in the duct 4 rises, but the check valve
prevents a corresponding rise in pressure in the
tube 34. Consequently, the diaphragm 30 is
unseated from the upper end of the duet 4, and air
enters the sewer 2 through the duct 4. At about
the same time as the air inlet valve opens, the
control unit 7 communicates atmospheric pressure to
the tube 13, causing the sewer valve 3 to close.
Atmospheric pressure is also communicated to the
control chamber 32, with a slight delay due to the
length of the tube 34, and the air inlet valve
closes.
The toilet lid 17 is in sealing relationship
with the rim of the toilet bowl 1, and the function
impulse 8 can only be generated when the lid 17 is
closed. When -the sewer valve opens and waste is
drawn into the sewer, air for transporting the
waste is induced into the toilet bowl through the
tube 18 and the check valve 19 and the pressure in
the sewer behind the waste remains close to
atmospheric.
The outlet 36 of duct 4 is sufficiently close
to the sewer valve that the operation of the sewer
valve directly induces operation of the air inlet
valve. Thus, when the sewer valve opens, it is the
rise in pressure in the sewer when the waste from
the toilet bowl passes outlet 36 that causes the air
inlet valve to open, and when the sewer valve closes
in response to control unit 7, the fall in pressure
(increased vacuum) in the sewer causes the air inlet
valve to close. Since the air inlet valve cannot
open until the waste has passed outlet 36, there is
no possibility of the air inlet valve opening too
soon arid interfering with reliable transportation of
waste from the toilet bowl into the sewer.
Since the tube 34 is narrow, it has a small
volume and therefore a sufficient degree of vacuum
can be communicated from tube 13 to chamber 32 to
ensure that the air inlet valve 6 opens when the
pressure in duct 4 rises without need for a vacuum
accumulator.
F2G. 2 illustrates schema~ieally an arrange~-
ment in which the sewer 2 has several branches 48
connected to respective toilet bowls 1 through
respective sewer valves 3. An air inlet valve 50
and a control unit 7 are associated with each
toilet bowl 1 and sewer valve 3. The arrangement
of the toilet bowl, sewer valve, control unit and
air inlet valve may be as shown in FIG. 1.
The air inlet valves operate independently of
f~
one another, so that, for example, application of
a function impulse to the control unit associated
with one of the air inlet valves has no effect on
the other air inlet valves.
Tt will be appreciated that the invention is
not restricted to the particular embodiments that
have been described, grad that variations may be
made therein without departing from the scope of
the invention as defined in the appended claims and
equivalents thereof.
