AU7147300A

AU7147300A - Vacuum sewer system

Info

Publication number: AU7147300A
Application number: AU71473/00A
Authority: AU
Inventors: Hans Tornqvist
Original assignee: Evac International Oy
Current assignee: Evac Oy
Priority date: 1999-11-30
Filing date: 2000-11-08
Publication date: 2001-05-31
Anticipated expiration: 2020-11-08
Also published as: HK1038602A1; TW415984B; HK1038602B; AU777155B2; CN1196838C; KR20010061991A; CN1303976A; FI106220B; KR100763727B1

Description

P/00/011 Regulation 3.2

AUSTRALIA

Patents Act 1990 COMPLETE

SPECIFICATION

FOR A STANDARD PATENT 9 9 **Goo:

ORIGINAL

0c.

TO BE COMPLETED BY APPLICANT Name of Applicant: EVAC INTERNATIONAL

OY

Actual Inventor: Hans Tomqvist Address for Service: CALLINAN LAWRIE, 711 High Street, Kew, Victoria 3101, Australia Invention Title: VACUUM SEWER SYSTEM The following statement is a full description of this invention, including the best method of performing it known to me:- 08/ 1/00,tdl 1671.cs.doc,l -la- 1670 GB 2000-10-20 VACUUM SEWER SYSTEM The invention relates to a method of operating a vacuum sewer system according to the preamble of claim 1.

In a vacuum sewer system the sewer pipe must be kept under partial vacuum in order to enable sewage transport, typical for a vacuum sewer system, to be ac- S 10 complished. Such vacuum sewer systems are disclosed for example in US 3,629,099, US 4,184,506 and US 4,034,421. The known solutions are, however, relatively complicated and expensive.

It is also known to use ejectors for generating vacuum in a vacuum sewer system. US 4,034,421 shows a system with a liquid driven ejector at the downstream end of the sewer, which ejector generates a partial vacuum necessary for sewage transport. This known arrangement is expensive because a separate circulation pump must be used for driving the ejector. Besides, the efficiency rate of the vacuum generation is low, only about 5 Furthermore, the working medium supplied to the ejector is untreated sewage, which sets special demands, e.g. with regard to cleaning etc., on the circulation pump and on the ejector. The use of another liquid as working medium would be possible, but it would necessitate that a supply of additional liquid be carried aboard the vehicle.

US 4,791,688 shows a similar system to US 4,034,421, in which, in addition, is employed an extra external air supply for ensuring sewage transport.

Further vacuum sewer systems are shown in SE 506 007, US 5,813,061 and US 5,873,135. In these known systems the required partial vacuum in the sewer pipe is generated by means of an air pressure driven ejector arranged as an integrated part of the sewer pipe, which is located relatively close to any unit to be emptied into the vacuum sewer. Such a unit may be a toilet bowl, the outlet of which is, via a normally closed sewer valve, connected to the vacuum sewer. These solutions are simpler and have a smaller number of parts than the systems described above. Nonetheless, these solutions require a large amount of air and also generate a considerable noise level.

The object of the invention is to provide a method of operating a vacuum sewer system, by which the above mentioned drawbacks are avoided and by which an improved vacuum generation, a reduced consumption of air and a lower energy consumption, as well as a lower operational noise level are attained. This object is achieved by a method according to claim 1.

The basic idea of the invention is to ensure a reliable operation of the vacuum 15 sewer system. In a vacuum sewer system generation of partial vacuum is the principal measure, however, malfunctions at the discharge end of the vacuum sewer system also have to be avoided. This is effectively done by ensuring the combined effect of partial vacuum in the system and pneumatic pressure at the *"discharge end of the system, which may be provided by providing pressurized working medium, e.g. pressurized air, for a time period substantially including completion of a flushing cycle. In order to ensure discharge, pressurized air may, if so desired, be supplied until any given time after the sewer valve is closed.

Pressurized air is preferably applied until shortly after the sewer valve is closed in order to sufficiently secure discharge of the sewage.

However, in view of the consumption of pressurized air, it may be advantageous to interrupt the supply somewhat before the closing of the sewer valve, which in most cases is sufficient.

In a vacuum sewer system, which at the downstream portion of the sewer pipe, within a zone where the function of the ejector causes the partial vacuum, further comprises an internal flexible sleeve member, an external surface of which lies opposite to a surrounding wall of a pipe portion, and at said zone an inlet in the wall of the pipe portion, it is advantageous to supply pressurized air in between the external surface of the flexible sleeve member and the surrounding wall of the pipe portion through the inlet so that pressurized air is supplied within a time period before the sewer valve is opened. This causes a contraction of the vacuum sewer pipe at the end of the zone where partial vacuum is gen- 10 erated, which enhances the generation of partial vacuum and lessens the consumption of air.

e *oo.

Pressurized air is advantageously provided at an overpressure in a range of about 0.0 to 2.0 bar, preferably in a range of about 0.0 to 0.7 bar. The degree 15 of overpressure may be chosen based on the wall thickness of the flexible sleeve member and the desired degree of contraction.

Pressurized air is advantageously supplied at a time of the flushing cycle when contraction is most effective, i.e. when partial vacuum is accumulated, i.e. before the sewer valve is opened.

The invention also relates to a vacuum sewer system according to claim 7, wherein the method according to the invention may be applied.

In the following, the invention will now be described, by way of example only, with reference to the accompanying schematic drawings, in which Fig. 1 shows a general layout of a compressed air system applied to a vehicle unit, Fig. 2 shows a vacuum sewer system, Fig. 3 shows a section of a relief valve for such a system, Fig. 4 shows an axial section of an ejector, Fig. 5 shows a side view of a rubber sleeve member being part of the ejector shown in Fig. 4, Fig. 6 shows an end view of the rubber sleeve member according to Fig. 5, in a contracted position, and Fig. 7 shows a diagram of the related operational sequences of the vacuum sewer system.

The compressed air system according to Fig. 1, in this case applied to a vehicle unit 30, e.g. a railroad car, includes a compressor 31, a compressed air tank 32, S 10 a pipe system 33 for distributing compressed air from the tank to various operating devices in the railroad car, e.g. a brake unit 34 connected to a wheel unit 35, door opening and closing mechanisms, i.e. a door actuator 36, and the like.

The vacuum sewer system, which is described in more detail in the following with reference to Figs. 2-7, may be arranged to be connected to such a compressed air system. Reference numeral 11, used correspondingly also in the following, indicates a working medium supply inlet, in this case a pipe connecting the compressed air system to the vacuum sewer system for supplying compressed air to an ejector that is part of the vacuum sewer system. The invention **does not require extra costs for the compressed air system, the capacity of which usually is very well sufficient for the limited use required by a vacuum sewer system. The compressed air capacity, if it would be necessary, may easily be increased by an additional compressed air tank or by enlarging the existing tank.

If, for some reason, it would be more convenient to use some other fluid than air, e.g. a gas, a gas mixture or liquid, as a working medium in the ejector, this may be realized as well within the scope of the invention.

In Fig. 2 reference numeral 1 indicates a waste receiving unit, e.g. a toilet bowl, the outlet opening 2 of which is normally closed by a sewer valve 3. The sewer valve may be e.g. a disc valve, which may be of the type described in US 4,713,847, a slide valve, a ball valve, a tube valve or the like. The upstream end of a vacuum sewer pipe comprises an upstream portion 4 of the sewer pipe, which is directly connected to the sewer valve 3. To empty the toilet bowl 1, a partial vacuum is generated in the upstream portion 4 of the sewer pipe by a pressurized air ejector 5, which forms an integrated part of said upstream portion. Downstream of the ejector 5 the sewer pipe comprises a downstream portion 7. The downstream portion 7 of the sewer pipe does not form a vacuum sewer, because it is at the pressure side of the ejector 5. The downstream portion 7 of the sewer pipe may lead to any desired location, preferably outside the 10 vacuum system and under atmospheric pressure. To give an example, the downstream portion 7 may lead to a collecting container 6. The collecting conl tainer 6 is outside the vacuum system and under atmospheric pressure through the air vent 6a.

15 In order to empty the toilet bowl 1, a user may operate a push button 8 or some other suitable device transmitting a signal to a control center 9, which controls all the functions of the system. The start-up system may for example be pneumatic as well. The control center 9 opens a remote-controlled air feed valve connected to the ejector 5, whereby pressurized air from the pipe 11 connected to the compressed air system rushes into the ejector 5. The compressed air operates as a working medium of the ejector and generates in a very short time a considerable partial vacuum in the ejector 5 and in the upstream portion 4 of the sewer pipe. After a desired vacuum level, i.e. a pressure reduction in the range of about 10% to 50%, preferably about 25% to 45% (corresponding to about 0.10 to 0.50 bar and 0.25 to 0.45 bar below atmospheric pressure respectively), has been obtained in the upstream portion 4, the sewer valve 3 is rapidly opened, and the ambient atmospheric pressure present in the interior of the toilet bowl 1 instantaneously causes the contents of the toilet bowl 1 to be pushed into the upstream portion 4 of the sewer pipe. The ejector 5 is then still in operation and maintains partial vacuum downstream of a plug of sewage that advances very rapidly from the toilet bowl 1 through the upstream portion 4 of 6 the sewer pipe. Simultaneously the ejector 5 blows the downstream portion 7 of the sewer pipe clean of any liquid or impurity that might be present there.

The pneumatic pressure created by the ejector 5 in the downstream portion 7 of the sewer pipe assists in transportation of sewage through said downstream portion.

When the ejector 5 is in operation and the sewer valve 3 is opened, the toilet bowl 1 is also supplied with a desired amount of rinse liquid in a manner that cleans the inner surface of the toilet bowl. This function is not described in de- 10 tail, because it is well known in the art and does not itself have any influence on the application of the invention.

.ooo The system may preferably also be provided with some arrangement to protect the system from undesirable pressure surges.

First of all, the upstream portion 4 of the sewer pipe may be provided with a pressure sensor 17 connected to the control center 9. At a rise of pressure in the upstream portion 4, the pressure sensor 17 rapidly closes the air feed valve thereby stopping further air delivery to the ejector 5. Such pressure surges may arise when a temporary stoppage or slowing down occurs in the sewage transport downstream of the ejector. In a situation like this, the operation of the ejector will rapidly increase the pressure in the sewer pipe and this pressure increase may propagate upstream of the ejector to any toilet bowl that is connected during flushing to the sewer pipe and consequently create an undesired pressure surge in the wrong direction (backflow or backflush) in the toilet. This problem is avoided by the simultaneous closing down of the ejector and the reduction of pressure.

An alternative arrangement for corresponding situations may be a relief valve. In Fig. 3 a simple relief valve in the form of a flexible hose 12 is shown. The hose 12 is surrounded by a protective tube 13 and is bent about 90' so that a fold 14 or kink is formed in the hose. The hose remains bent because of the weight of the part of the hose to the right of the fold 14. The interior of the hose 12 is connected via an aperture 15 to the interior of the upstream portion 4 of the sewer pipe. The fold 14 totally closes the hose 12, thus functioning like a nonreturn valve since the outer atmospheric pressure closes the fold, especially when the pressure outside the hose is higher than in the interior of the upstream portion 4. If overpressure occurs in the upstream portion 4, the hose 12 is under the influence of this pressure and is then somewhat straightened to adopt the position 12a shown in dashed lines. In this position 12a an aperture 14a is opened up, thus forming a through-flow duct, at the point where the hose is normally closed by the fold 14. The overpressure can then discharge through the aperture 14a. The protective tube 13 has a continuation 13a that connects it in a suitable manner to the downstream portion 7 of the sewer pipe, as •..*shown in Fig. 2, or directly to the collecting container 6 or other desired location 15 in a manner that allows gravity induced flow.

Naturally, a combination of the arrangements described above may also be used to increase operational reliability.

As explained more in detail with reference to Fig. 7, the ejector 5 may advantageously be closed shortly before or shortly after the closing of the sewer valve 3. In this time the sewage reaches and passes the ejector 5. Because the sewage is driven forwards by the ambient atmospheric pressure, it is important, that the sewer valve 3 is kept open a sufficient length of time so that a sufficiently large amount of air flows, via the outlet opening 2 of the toilet bowl 1, into the upstream portion 4 of the sewer pipe. When the sewer valve 3, upon emptying of the toilet bowl 1, is again closed, the control center 9 keeps it closed preferably for a given time to ensure that all the sewage is discharged from the downstream portion 7 of the sewer pipe, for example into a collecting container 6, before a following flushing cycle is initiated.

8 Fig. 4 shows a preferred embodiment of an ejector 5 according to the invention.

The upstream portion 4 of the sewer pipe forms an angle of 1350 relative to the downstream portion 7 of the sewer pipe. In the embodiment shown the upstream portion 4 is mainly horizontal and the downstream portion 7 is inclined downwards in the flow direction. It is also feasible for the upstream and downstream portions 4 and 7 of the sewer pipe to be substantially parallel, but at different levels and/or in different vertical planes, whereby the upstream portion 4 of the sewer pipe just upstream of the ejector 5 is bent about 450 for its connection to the ejector. However, the embodiment shown in Fig. 4 has proved to i~ o 10 be advantageous with respect to operational reliability.

The ejector may,however, be devised in different manners according to the following principles. If the suction pipe joins the discharge pipe at an angle, it is :suitable that the upstream portion of the sewer pipe connected to the ejector 15 and the downstream portion of the sewer pipe at the downstream side of the ejector form an angle of at least 1200, preferably at least 1350 (as above). At l smaller angles there is a greater risk for disturbances in the flow of sewage l through the sewer pipe. If the sewer pipe runs substantially linearly through the ejector and the working medium of the ejector is supplied either through nozzles arranged circumferentially in the sewer pipe or through a nozzle that from the exterior of the sewer pipe extends through the pipe wall into the interior of the sewer pipe, it is important that the nozzle member is provided with such diverting surfaces that the risk for sewage matter getting caught by the nozzle member or by its attachment members is practically eliminated.

The working medium of the ejector 5 is compressed air, which is introduced into the ejector through the pipe 11 at a dynamic pressure in a range of about 3 to bar, preferably in a range of about 4 to 6 bar. It is introduced through an aperture with a diameter of only some millimeters, e.g. less than 5 mm, at the end of the pipe 11 into the ejector 5 and flows mainly in the longitudinal direction of the downstream portion 7 of the sewer pipe. Immediately downstream of the pipe 11 the ejector function generates the partial vacuum including a zone, comprising a pipe portion 16, of a length of some tens of centimeters. About in the middle, in the longitudinal direction, of this zone there is a flexible rubber sleeve member 18, an external surface of which lies opposite the surrounding wall of the pipe portion 16.

In the area of this zone, comprising the sleeve member 18, the pipe portion 16 is provided with an inlet 19, which is connected to a pipe section 11 a providing pressurized air. This pipe section 11a is diverted from pipe 11, connecting the S 10 compressed air system to the vacuum sewer system, upstream of the air feed valve 9 In order to form the sleeve member 18 by contraction a space 26 (indicated by dashed lines in Fig. i.e. a pressure chamber, may be formed between the external surface of the flexible sleeve member 18 and the surrounding wall of the pipe portion 16 by the pressurized air obtained through the inlet 19 from the Spipe section 11 a. The pipe section 11 a is preferably provided with a pressure 9 regulator 24 and a three-way shut-off valve 23. The shut-off valve 23 is provided with means for ventilation, into the atmosphere, of the pipe section 16 in its closed position. The pressurized air is applied to the outer side of the flexible sleeve member 18 and to said space 26 to more efficiently form, i.e. cause contraction of the flexible sleeve member than would be the case solely by the underpressure or vacuum inside the flexible sleeve member. The shut-off valve 23 is in connection with the control center 9 and thus the pressure can be applied at a time of the flushing cycle when a contraction of the flexible sleeve is most advantageous, i.e. when generation of partial vacuum is started and until the sewer valve 3 is opened. The pressure regulator 24, which is coupled in series with the shut-off valve 23, is used to regulate the pressure around the flexible sleeve member 18. The pressure is advantageously regulated at an overpressure in a range of about 0 bar to about 2 bar, preferably in a range of about 0 bar to about 0.7 bar, depending on the general dimensioning and layout of the vacuum sewer system.

The pressurized air, as described above, is applied around the flexible sleeve member 18 from the pipe section 11 a and through the inlet 19 in the wall of the surrounding pipe portion 16 and is induced at the same time when the air feed valve 10 opens to the pipe 11. The pressure is maintained on the flexible sleeve member 18 until the sewer valve 3 is opened, whereby the shut-off valve 23 is .closed resulting in ventilation of the inside of the pipe 16 (cf. Fig. 7 where the 10 pressurized air surrounding the flexible sleeve member 18 is shown by the horizontal column 23a). The pressure is preferably maintained through the air feed valve 10 from the pipe 11 until shortly before or shortly after the sewer valve 3 has been closed.

°o00 The pressure around the flexible sleeve member 18 is normally adjustable in a time-controlled manner, but may also be controlled from the control center 9 by means of a security device in the form of a vacuum guard 25 provided at the upstream portion 4 of the sewer pipe and shown beside the pressure sensor 17 described above. The vacuum guard 25 senses the vacuum level at which the o 20 pressure is to be closed off and the pipe portion 16 is to be ventilated into the atmosphere.

Because the sleeve member 18 is bent over or doublebent at its downstream end, as shown in Figs. 4 and 5, it has a relatively large freedom of motion. The vacuum generated by the ejector 5 in cooperation with the pressure created by the pressurized air, which through the inlet 19 influences the sleeve member 18, causes the sleeve member to contract by forming folds, as shown in Fig. 6, and thereby produces a pressure induced reduction in the cross-sectional area of the discharge pipe of the ejector. The contracting function of the sleeve member has a very advantageous influence on the effectivity of the ejector 5 and contributes to reducing the air consumption of the ejector. When sewage passes 11 through the sleeve 18, the folded sleeve member expands so that larger solid ingredients are also able to pass without difficulty through it. The pressure induced forming, i.e. contraction of the sleeve member 18, gives an improved degree of control of the contraction and enhances the vacuum generation of the ejector, thereby lessening the consumption of air. The controlled function of the flexible sleeve member 18 decreases the vibrations of the same leading to a diminished noise level.

.As is apparent from Fig. 5, the sleeve member 18 includes, at its inlet end, a 10 stiffener comprising a cylindrical portion 21 from which four circumferentially spaced-apart, axial portions 22 extend to almost the longitudinal middle portion of the sleeve member in its double-bent position. The stiffener is an integral part of the sleeve member 18 and is formed by locally increasing the thickness of *the same. The axial portions 22 of the stiffener guide contraction of the sleeve member 18, so that regular folds and a free opening 20 according to Fig. 6, where the sleeve member 18 is seen from its downstream end, are obtained. In the embodiment according to Fig. 4, the downstream portion 7 of the sewer pipe is about 40 larger in diameter than the upstream portion 4 of the sewer pipe. This reduces the risk of flow stoppage or too slow flow in the sewer pipe.

Such a flexible sleeve member, or hose, essentially improves the effect of the ejector, and the amount of pressurized air used may then be reduced, in many cases with up to 2/3. The flexible sleeve member 18 is preferably mounted immediately downstream of the section where the suction pipe of the ejector joins the discharge pipe of the ejector. For obtaining the best action of the flexible sleeve member, the upstream portion of the flexible sleeve member includes said axially orientated stiffener portions which provide the guiding effect on the contraction motion of the flexible sleeve member, especially in its starting phase.

To give an example, the contraction of a suitably devised flexible rubber sleeve member 18 with a wall thickness of about 1 mm, stiffener portions 21,22 with a wall thickness of about 2 mm and a length of about 110 mm, and mounted in a sewer pipe with a bore diameter of 54 mm, may result in that the free opening 20 in the center has a diameter of only about 10 mm. A sleeve member 18 with a wall thickness of only about 1 mm may be easily formed, but on the other hand, it is very vulnerable to wear and tear as well as to e.g. sharp objects which may be flushed down with the sewage. Therefore, it may be advantageous to increase the thickness of the flexible sleeve member 18, even up to 12 10 mm, preferably in a range of 0.5 to 12 mm. The pressure applied to the sleeve member 18, in order to cause its contraction, has consequently to be increased.

°oooo This may effectively done as described above. A further advantage with a sleeve member having an increased wall thickness is its stability, i.e. lessened *vibration, which considerably reduces the noise level of the vacuum sewer system.

Fig. 7 shows the operational sequences of the flushing cycle of a toilet bowl 1 in a system according to Fig. 2. The time values given in the following are only "r given as examples in order to illustrate a general time scope of the flushing cycle.

The flushing cycle is started by operating the push button 8 for a short period of time, a fraction of a second, as shown by column 8a. This activates the ejector which operates for about 5 to 6 seconds, as indicated by columns 5b and respectively. At the same time pressurized air is also applied around the flexible sleeve member 18, as indicated by column 23a, through pipe section 11 a and inlet 19 in order to achieve a controlled contraction of the sleeve member 18 and thus to make the vacuum generation of the ejector 5 more effective and stable. About 2.5 seconds after the ejector 5 has been activated, the sewer valve 3 is opened and is kept open for about 3 seconds as indicated by section 3a. When the sewer valve 3 is opened the supply (23a) of pressurized air on the sleeve member 18 is closed down and the space 26 formed during contraction is ventilated to the atmosphere through the three-way shut-off valve 23. The function of the ejector reduces the pressure in the upstream portion 4 of the sewer pipe by about 40 kPa as shown by the curve 4a before the sewer valve 3 opens. When the sewer valve 3 opens, the pressure in the upstream portion 4 starts to increase, and, within the time the sewer valve 3 is kept open, reaches its original value. After the sewer valve 3 has been closed, the pressure may decrease slightly within a time period of about 0.5 seconds due to the pressure induced by the ejector 5, provided it is kept in operation (column 5c) until 10 (shortly after) the sewer valve 3 is closed. The longer operational period (column 5c) of the ejector 5 may be advantageous to ensure that all waste has been appropriately discharged from the sewer pipe. Alternatively the ejector 5 may be kept in operation a shorter period (column 5b), closing (shortly, e.g. about seconds) before the sewer valve 3 is closed. Thereafter, the system may be e• 15 locked for a given time T, for example about 5 seconds, in order to avoid very closely repeated flushes, which could cause operational disturbances in the system.

"The ejector 5 may also be operated for any length of time (column 5a) after the 20 sewer valve 3 is closed, if this would be advantageous for discharge purposes.

However, this would of course influence air and energy consumption, which will be discussed more in detail below.

The rate of supply of air to the ejector may be of a magnitude in the range of about 500 to 1500 liters/minute, wherein the volume of air is calculated at standard temperature and pressure (01C, standard atmosphere). It is of course of advantage to reduce the amount of air fed to the ejector as much as possible, without thereby taking any risks with respects to the secure functioning of the system, since the smaller the consumption of air, the smaller is the energy consumption.

The energy consumption of an emptying cycle is also influenced by the volume of the space that is to be placed under partial vacuum. The smaller this volume is, the smaller the energy consumption. The portion of the sewer pipe, which is placed under partial vacuum, must not, however, be too short, since the vacuum volume will then be too small for obtaining effective emptying of a toilet bowl.

In the embodiment shown, in order to provide an example, and in the case a collecting container 6 is used, the distance L between the sewer valve 3 and 10 the ejector 5 may e.g. be about 1 to 10 m, preferably in the range of about 2 m. The downstream portion 7 of the sewer pipe may then be even several meters so that the ejector 5 is positioned between the ends of, and not at the other end of, the sewer pipe extending from the sewer valve 3 to the collecting container 6 and formed of the upstream and downstream portions 4 and 7 of the sewer pipe.

However, it is of advantage to position the ejector relatively close to the discharge end of the sewer pipe, i.e. for example as close as possible to the col- **lecting container, since this would ensure appropriate and effective discharge of S 20 the waste. Also, by designing the downstream portion 7 of the sewer pipe as short as possible, the consumption of air may be minimized. The ejector could even be placed in the collecting container, whereby the length of said downstream portion would practically be close to 0 m. On the other hand, for service and/or repair of the ejector, it may be preferable that the ejector be positioned relatively close to the toilet bowl or any other waste receiving unit that is to be emptied into the vacuum sewer.

The above mentioned related values are only given as examples, and are dependent on the dimensioning and layout of the vacuum sewer system.

For instance, the time values discussed above with reference to Fig. 7 are, amongst other things, directly dependent on the respective lengths of the sewer pipe portions. To illustrate this the following example may be given.

The length of the upstream portion 4 of the sewer pipe being e.g. 2 m, the length of the downstream portion 7 of the sewer pipe being e.g. close to 0 m the ejector 5 forming the end of the sewer pipe or the ejector 5 being placed in the collecting container the operation time of the ejector could be 4 seconds and the opening time 3a of the sewer valve 2 seconds. The ejector could then be closed down at the same time as the sewer valve 3 is closed, 10 since there would be no further transport distance for the sewage.

some o o The longer the upstream portion 4 is, the greater the relative volume of the space that has to be put under partial vacuum, which means a longer opera- 0*0S tional time for the ejector. The same applies for the downstream portion, if ef- 15 fective discharge has to be ensured at all times. This of course also influences the operational time of the sewer valve. The configuration, i.e. angles, bends, 5 straight portions, etc., of the vacuum sewer also have a bearing on the operational time periods.

More than one toilet bowl, or other waste receiving unit, may be included in a vacuum sewer system according to the invention. Thus, the upstream portion of the sewer pipe may be branched and multiple branches connected to respective toilet bowls, although the number of toilet bowls should not be too great or the consumption of compressed air will be excessive. Typically, therefore, a pair of toilet bowls will be connected to an ejector via an upstream portion having two branches. Preferably, the control center prevents the two toilet bowls from being emptied at the same time. Also, the invention may be applied to various types of vehicles, including marine units, as indicated above, and also to stationary installations.

The invention is not limited to the embodiments disclosed, but several modifications thereof are feasible within the scope of the attached claims.

Where the terms "comprise", "comprises", "comprised" or "comprising" are used in this specification, they are to be interpreted as specifying the presence of the stated features, integers, steps or components referred to, but not to preclude the presence or addition of one or more other feature, integer, step, component or group thereof.

.e e 8/11/00,td11671. com2.doc,15

Claims

1. A method of operating a vacuum sewer system that comprises a waste receiving unit to be emptied from time to time through an outlet opening thereof, a sewer valve for controlling the flow of sewage from the waste receiving unit through said outlet opening a sewer pipe having an upstream portion connected to the sewer valve and a downstream portion providing a discharge end of the sewer pipe, and an ejector having a working medium supply inlet (11) and being integrated into the sewer pipe so that the upstream portion of the sewer pipe provides a suction pipe of the ejector and the downstream portion of the sewer pipe a °ego 15 discharge pipe of the ejector, in which method working medium is supplied to the ejector through the working "medium supply inlet (11) creating a partial vacuum in the upstream portion (4) 00000 of the sewer pipe, o* 20 the sewer valve is opened, whereby ambient atmospheric pressure pushes sewage in the waste receiving unit into and through the upstream portion of the sewer pipe, sewage is further transported through the downstream portion of the sewer pipe assisted by pneumatic pressure created by the ejector in the downstream portion of the sewer pipe, and in which method the sewer valve is closed upon emptying of the waste receiving unit characterised in that working medium is supplied to the ejector for a time period substantially including a time period (3a) the sewer valve is open maintaining 17 pneumatic pressure in the downstream portion of the sewer pipe for said time period.

2. A method according to claim 1, characterised in that working medium is supplied to the ejector until shortly before (5b) the sewer valve is closed.

3. A method according to claim 1, characterised in that working medium is supplied to the ejector until shortly after (5c) the sewer valve is 10 closed. .°oooo

4. A method according to claim 1, wherein the vacuum sewer system at the downstream portion of the sewer pipe, within a zone where the function of the ejector causes the partial vacuum, further comprises an internal 15 flexible sleeve member an external surface of which lies opposite to a surrounding wall of a pipe portion and at said zone an inlet (19) in the wall of the pipe portion characterised in that pressurized air is supplied in between the external surface of the flexible sleeve member (18) and the surrounding wall of the pipe portion (16) through the inlet (19) and in that pressurized air is supplied within a time period (23a) before the sewer valve is opened. A method according to claim 4, characterised in that pressurized air is sup- plied at an overpressure in a range of about 0.0 to 2.0 bar, preferably in a range of about 0.0 to 0.7 bar.

6. A method according to claim 5, characterised in that pressurized air is sup- plied within a period (23a) starting at the same time as the period (5a-5c) for supplying working medium starts and ending at the time of the opening of the sewer valve and in that the supplied pressurized air is ventilated to the atmosphere at the end of the supply period (23a).

7. A vacuum sewer system comprising a waste receiving unit to be emptied from time to time through an outlet opening thereof, a sewer valve for controlling the flow of sewage from the waste receiving unit through said outlet opening a sewer pipe having an upstream portion connected to the sewer valve and a downstream portion providing a discharge end of the sewer pipe, and an ejector having a working medium supply inlet (11) and being integrated into the sewer pipe so that the upstream portion of the sewer pipe provides a suction pipe of the ejector and the down- 10 stream portion of the sewer pipe a discharge pipe of the ejector, charac- terised in that the downstream portion of the sewer pipe, within a zone where the function of the ejector causes a partial vacuum, comprises an S internal flexible sleeve member an external surface of which lies oppo- site to a surrounding wall of a pipe portion and in that at said zone an 15 inlet (19) for pressurized air is arranged in the wall of the pipe portion (16) °for supplying pressurized air in between the external surface of the flexible sleeve member (18) and the surrounding wall of the pipe portion (16). o *SSS**

8. A system according to claim 7, characterised in that the flexible sleeve 00 20 member (18) has a wall thickness in a range of about 0.5 to 12 mm.

9. A system according to claim 7, characterised in that an air feed valve (10) is provided between the working medium supply inlet (11) and the ejector the inlet (19) in the wall of the pipe portion (16) is connected to a pipe sec- tion (1 la) which is connected to the working medium supply inlet and in that the pipe section (11 a) is diverted from the working medium inlet (11) upstream of the air feed valve A system according to claim 9, characterised in that the pipe section (11 a) is provided with a pressure regulator (24) and a three-way shut-off valve (23). 19

11. A system according to claim 10, characterised in that the shut-off valve (23) is in connection with a control center of the vacuum sewer system, which control center also is in connection with the air feed valve

12. A system according to claim 11, characterised in that the upstream portion of the sewer pipe is provided with a security device (25) con- nected to the control center and to the shuf-off valve and in that S 10 the security device is a vacuum guard

13. A system according to claim 7, characterised in that the system com- prises a sewage collecting container connected to the downstream por- tion of the sewer pipe. p Dated this 8 th day of November, 2000. S EVAC INTERNATIONAL OY By their Patent Attorneys: CALLINAN LAWRIE