GB2452257A

GB2452257A - Collection plant for vacuum-discharge toilet system

Info

Publication number: GB2452257A
Application number: GB0716564A
Authority: GB
Inventors: Martin Lowe
Original assignee: Individual
Current assignee: Individual
Priority date: 2007-08-25
Filing date: 2007-08-25
Publication date: 2009-03-04
Also published as: WO2009027716A9; GB201003008D0; WO2009027716A1; GB2467055A; EP2188458A1; GB0716564D0

Abstract

A collection plant (20) for a sanitary system (10) employing at least one vacuum toilet pan (12) comprises an air pump (28), which serves both to maintain a vacuum at the vacuum toilet pan(s) so as to suck waste from the vacuum toilet pan(s) to the collection plant and, while maintaining the vacuum for the vacuum toilet pan(s), also intermittently to create a super-atmospheric pressure which can be used to discharge the collected waste from the collection plant to a disposal tank (32) or sewage treatment plant. Preferably the plant includes an upper chamber (24) to receive the waste and a lower chamber (26) having a discharge outlet (39) so that the plant is operable in a collect-and transfer-mode or a collect-pressurise-and-discharge mode. Because of the creation of a super-atmospheric discharge pressure, there is no need for the disposal tank or sewage treatment plant to be at a lower level than the collection plant and no need to rely on gravity for discharge. It is to be noted that a single pump is used for both purposes and that it is an air pump, rather than a pump directly acting on the waste, which therefore facilitates and makes more pleasant the maintenance of the pump.

Description

TITLE

Sanitary system with collection plant

DESCRIPTION

This invention relates to sanitary systems and to collection plants for use in such systems.

There are occasions when the rapid deployment of sanitary facilities is required.

Examples are toilet facilities that need to be provided for field hospitals and medical shelters set up in response to natural disasters, civil unrest, and warfare, and for first-aid shelters at remote camps of commercial projects. Existing facilities include: * Modular grouped trailer facilities using conventional flush and gravity drainage. Such trailer facilities need to be located on level prepared sites to allow gravity drainage.

They employ conventional toilets which typically consume up to 2 to 5 gallons (9 to 23 litres) of fresh water per flush. Trailer facilities tend to group the ablutions, and, as a result, toilets cannot be located within tented areas. These facilities do not suit small scale or temporary camp areas due to their size and "hook-up" requirements.

* Chemical porta-potti/porta-loo facilities which again have to be grouped. These facilities require chemicals for the breakdown of ftecal matter and have to be emptied on a regular basis. They can create an unpleasant smell and are unhygienic to use. The contents are difficult to dispose of in remote areas. Portaloos tend to be grouped and are desirably not located in tented areas due to smells and contamination. They are often unsuitable for use by disabled or injured personnel due to location of facilities. Bedpans would have to be used which are difficult to dispose and also spread contamination.

* A hole in the ground or the traditional "thunderbox." This can be extremely unpleasant to use and provides ideal cultures for disease and contamination. The hole in the ground needs to be located well away from living areas and is often unsuitable for use by disabled or injured personnel due to location of facilities and unhygienic conditions.

Faecal matter/arisings need to be incinerated which is an unpleasant task.

A general aim of the present invention, or at least of specific embodiments of it, is to provide a sanitary system, and a collection plant for use in such a system, that overcomes, at least to some extent, the disadvantages of the known facilities described above. As is known per se for sanitary systems used in airliners and ships, the system of the present invention employs a partial vacuum (hereinafter referred to for simplicity as "a vacuum") to collect waste from vacuum toilet pans to a collection plant. This has the advantages that the vacuum toilet pans can be disposed at a higher or lower level than the collection plant, rather than relying on gravity, and that less water is typically required for each flush of the vacuum toilet pans, typically 1.2 litres. Having collected the waste at the collection plant, it is then necessary to discharge it, for example to a portable, removable tank, or to a permanent or temporary sewage treatment plant.

A specific aim of the invention, or at least of specific embodiments of it, is to facilitate the discharge of such waste.

In accordance with a first aspect of the present invention, there is provided a collection plant for a sanitary system employing at least one vacuum toilet pan, the collection plant employing an air pump, the pump serving both to maintain a vacuum at the vacuum toilet pan(s) so as to suck waste from the vacuum toilet pan(s) to the collection plant and, while maintaining the vacuum for the vacuum toilet pan(s), also intermittently to create a super-atmospheric pressure which is used to discharge the collected waste from the collection plant for subsequent treatment or disposal. During normal operation, a single air pump therefore acts to maintain the vacuum for the vacuum toilet pan(s) so that the vacuum toilet pan(s) can be operated at any time, but also acts to create a discharge pressure for discharging the waste for example to a disposal tank or a sewage treatment plant. Because of the creation of a super-atmospheric discharge pressure, there is no need for the disposal tank or sewage treatment plant to be at a lower level than the collection plant and no need to rely on gravity for discharge. It is to be noted that a single pump is used for both purposes and that it is an air pump, rather than a pump directly acting on the waste, which therefore facilitates and makes more pleasant the maintenance of the pump.

In a preferred embodiment of the invention, the collection plant includes an upper chamber for connection to receive waste from the vacuum toilet pan(s), a lower chamber generally below the upper chamber and having a discharge outlet, and a plurality of valves and pipes interconnecting the chambers and the pump so that the plant is operable in: (i) a collect-and-transfer mode in which the pump maintains a vacuum in both chambers, so that waste can be collected from the vacuum toilet pan(s) to the upper chamber, and waste can transfer from the upper chamber to the lower chamber; and (ii) a collect-pressurise-and-discharge mode in which the pump maintains a vacuum in the upper chamber so that waste can be collected from the vacuum toilet pan(s) to the upper chamber, waste in the upper chamber is isolated from the lower chamber, the pump pressurises the lower chamber, and waste can be discharged from the lower chamber through the discharge outlet utilising the pressure built up in the lower chamber.

The collection plant could be manually changed between modes, but preferably at least some of the valves (and more preferably all of the relevant valves) are motorised valves, and the plant further includes a plurality of sensors and control means for controlling the motorised valves in dependence upon the sensors to change the plant from at least one of the modes to the other mode automatically. The collection plant can therefore operate partly-or fully-automatically.

The motorised valves are preferably controlled to perform at least one (and more preferably all) of the following functions: (i) to connect the upper chamber to the lower chamber when in the collect-and-transfer mode, but not when in the collect-pressurise-and- discharge mode; (ii) to prevent discharge of waste from the lower chamber when in the collect-and-transfer mode; (iii) to connect the lower chamber to the inlet side of the pump when in the collect-and-transfer mode; (iv) to vent the outlet side of the pump to atmosphere when in the collect-and-transfer mode; and (v) to connect the outlet side of the pump to the lower chamber at least part of the time when in the collect-pressurise-and-discharge mode. When the outlet side of the pump is connected to the lower chamber, air sucked by the pump from the vacuum toilet pan(s) to the upper chamber is used to pressurise the lower chamber.

The control means is preferably arranged to respond to the sensors in at least one (and more preferably both) of the following ways: (i) when in the collect-and-transfer mode to change the plant to the collect-pressurise-and-discharge mode when the level of waste in the lower chamber is sensed to have risen to a particular level; (ii) when in the collect-pressurise-and-discharge mode to change the plant directly or indirectly to the collect-and-transfer mode when the level of waste in the lower chamber is sensed to have fallen to a particular level.

Preferably, the collect-pressurise-and-discharge mode includes: (i) a collect-and-pressurise sub-mode in which the pump maintains a vacuum in the upper chamber so that waste can be collected from the vacuum toilet pan(s) to the upper chamber, waste in the upper chamber is isolated from the lower chamber, and the pump pressurises the lower chamber; and (ii) a collect-and-discharge sub-mode in which the pump maintains a vacuum in the upper chamber so that waste can be collected from the vacuum toilet pan(s) to the upper chamber, waste in the upper chamber is isolated from the lower chamber, and waste can be discharged from the lower chamber through the discharge outlet utilising the pressure built up in the lower chamber during the collect-and-pressurise sub-mode. In this case, the motorised valves are preferably controlled to perform at least one (and more preferably both) of the following functions: (i) to connect the outlet side of the pump to the lower chamber when in the collect-and-pressurise sub-mode; and (ii) to prevent discharge of waste from the lower chamber when in the collect-and-pressurise mode, but permit such discharge when in the collect-and-discharge mode. Also, the control means is preferably arranged to respond to the sensors in at least one (and more preferably both) of the following ways: (i) when in the collect-and-pressurise sub-mode to change the plant to the collect-and-discharge sub-mode when the pressure in the lower chamber is sensed to have risen to a particular level; and (ii) when in the collect-and-discharge sub-mode to change the plant to the collect-and-pressurise sub-mode when the pressure in the lower chamber is sensed to have fallen to a particular level.

The plant may be operable in the collect-and-discharge sub-mode such that the pump does not pump air to the lower chamber, or alternatively so that it does pump air to the lower chamber so as to assist the discharge. In the latter case, the plant is preferably further operable in a collect-and-depressurise mode in which the pump maintains a vacuum in the upper chamber so that waste can be collected from the vacuum toilet pan(s) to the upper chamber, waste in the upper chamber is isolated from the lower chamber, and waste can be discharged from the lower chamber through the discharge outlet utilising the pressure remaining in the lower chamber from the collect-and-discharge sub-mode. This enables the lower chamber to depressurise after the pump has stopped pumping air to it, before the plant reverts to the collect-and-transfer mode.

In accordance with a second aspect of the invention, there is provided a sanitary system comprising at least one vacuum toilet pan and a collection plant according to the first aspect of the invention for connection to the vacuum toilet pan(s).

The sanitary system preferably further includes: at least one flexible pipe for connecting the vacuum toilet pan(s) to the collection plant; a flushing system for flushing the vacuum toilet pan(s); andlor a tank for receiving waste discharged by the collection plant.

A container is preferably provided for containing the sanitary system for transportation.

A specific embodiment of the present invention will now be described, purely by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic block diagram of a sanitary system of the embodiment of the invention; Figure 2 is a front elevation of a collection plant of the system of Figure 1; -5.

Figure 3 is a side elevation of the collection plant; Figure 4 is plan view of the collection plant; Figure 5 is a state diagram to illustrate the principle operations of the collection plant; Figure 6 is a schematic block diagram of the collection plant, emphasising a collect-and-transfer' state of the unit; Figure 7 is similar to Figure 6, but emphasising a collect-and-pressurise' state of the unit; Figure 8 is similar to Figure 6, but emphasising a collect-and-discharge' state of the system; Figure 9 is a schematic isometric view of the sanitary system packed away in a container, the container being shown in dashed lines; and Figure 10 is another state diagram to illustrate modified operation of the collection plant.

Referring to Figure 1, a mobile sanitary system 10 includes a number of conventional vacuum-operated toilet pans 12, which can receive flushing water from a water tank 14. The water tank 14 receives water through a supply pipe 16 and is pressurised with air by a pump 18 so that in operation the water tank does not need to be at a higher level than the vacuum toilet pans 12. The system 10 also includes a collection plant 20 delineated by dot-dash lines in Figure 1 and also shown in Figures 2 to 4. The collection plant 20 comprises a tank assembly 22 having an upper chamber 24 and a lower chamber 26, a pump 28, a control unit 30, and a number of motorised valves, float switches and pressure switches which will be described in further detail below. The pump 18 for the water tank 14 may be provided as part of the collection plant 20, or may be mounted elsewhere. The pumps 18,28 may be electrically powered, for example by a high-voltage supply from the mains or a generator, or by a low-voltage supply from one or more batteries. The system 10 furthermore includes a pillow tank 32 having a vent pipe 34. The waste outlets 36 of the vacuum toilet pans are branched into a flexible suction pipe 38 which is connected to the top of the upper chamber 24. The pillow tank 32 is connected to a discharge port 39 at the bottom of the lower chamber 26 via a motorised valve 40 and a flexible discharge pipe 42. The pillow tank 32 is such that, after it has been filled, it can be disconnected from the discharge pipe 42 and vent pipe 34, sealed, and transported away for subsequent processing of the contents. As an alternative to the use of the pillow tank 32, the discharge pipe 42 may be connected to a permanent or temporary sewage treatment plant.

The upper chamber 24 is connected at its bottom to the lower chamber 26 via a transfer pipe 44 and motorised valve 46. The pump 28 is of a type that can act both as a suction or vacuum pump to decrease the pressure at its inlet substantially below atmospheric pressure and as a compressor to increase the pressure at its outlet substantially above atmospheric pressure.

The inlet of the pump 28 is connected via a check-valve 48 to a port 50 at the top of the upper chamber 24 and also via the check-valve 48 and a motorised valve 52 to a port 54 at the top of the lower chamber 26. The outlet of the pump 28 is connected via a motorised valve 56 to a vent pipe 58 and also via a further motorised valve 60 and a check-valve 62 to the port 54 at the top of the lower chamber 26.

The lower chamber 26 is fitted with a pair of float switches 64,66 to detect when the lower chamber 26 is substantially full and substantially empty, respectively. Other float switches may be fitted to detect when there is a problem with the system 10, such as float switch 68 to detect if the upper chamber 24 becomes substantially full. The lower chamber 26 is also fitted with a pressure switch 70 to detect when the pressure in the lower chamber 26 rises to a predetermined pressure, for example +0.9 bar (gauge), and a pressure switch 72 to detect when the pressure in the lower chamber 26 falls to a predetermined pressure, for example +0.3 bar (gauge). The upper chamber 24 is also fitted with a pressure switch 74 to detect when the pressure in the upper chamber 24 falls below a predetermined pressure, for example -0.6 bar (gauge). The pressure switch 74 may have hysteresis over the range -0.6 to -0.35 bar (gauge).

The various motorised valves 40,46,52,56,60, float switches 64,66,68, pressure switches 70,72,74 and pumps 18,28 are connected to the control unit 30. The system may be fitted as appropriate with visually-readable pressure gauges and pressure-relief, or safety, valves. As shown in Figures 2 to 4, the collection plant 20 is mounted on a skid assembly 76. In an embodiment of the invention, the capacities of the upper chamber 24, lower chamber 26 and pillow tank 32 are about 360, 370 and 2,000 litres, respectively.

The operation of the collection plant 20, under control of the control unit 30, will now be described with reference to Figures 5 to 8. In the state diagram of Figure 5, the various states of the system are shown by the boxes, and the condition that needs to be met to change from one state to another is marked on the arrowed line between those two states. In Figures 6 to 8: pipes in which there is no significant flow are shown in dashed lines; in pipes where there is or can be significant flow, the direction of flow is shown by arrows; and the motorised valves which are closed are shown shaded black, whereas motorised valves which are open are shown unshaded.

As shown in the state diagram of Figure 5, the collection plant 20 has three principal states: a collect-and-transfer state 78; a collect-and-pressurise state 80; and a collect-and-discharge state 82.

In the collect-and-transfer state 78, which is also shown in Figure 6, the motorised valves are set so that the valves 46,52,56 are open, whereas the valves 40,60 are closed.

Accordingly, the pump 28 creates a vacuum in the upper and lower chambers 24,26 and exhausts air to the atmosphere via the vent pipe 58. The control unit 30 switches the pump 28 on and off in dependence upon the pressure switch 74 to maintain the pressure in the upper and lower chambers 24,26 between about -0.35 and -0.6 bar (gauge). The vacuum in the upper chamber 24 applies suction to the waste outlets 36 of the vacuum toilet pans 12 via the pipe 38.

Therefore, when any of the vacuum toilet pans 12 is actuated in the conventional way, the waste is sucked through the pipe 38 into the upper chamber 24. Because the valve 46 is open and the upper and lower chambers 24,26 are at substantially the same pressure, waste in the upper chamber 24 drains via the transfer pipe 44 and valve 46 to the lower chamber 26. The collection.

plant 20 remains in the collect-and-transfer state 78, with the lower chamber 26 filling with waste as the vacuum toilet pans 12 are operated, until the control unit 30 detects from the float switch 64 that the lower chamber 26 is substantially full, whereupon the control unit 30 changes the collection plant 20 to the collect-and-pressurise state 80.

Upon changing to the collect-and-pressurise state 80, which is also shown in Figure 7, the motorised valves are set so that the valve 60 is open and the valves 40,46,52,56 are closed.

Accordingly, waste can no longer drain from the upper chamber 24 to the lower chamber 26.

However, a vacuum is maintained in the upper chamber 24 so that the vacuum toilet pans 12 will still function. Furthermore, the lower chamber 26, instead of being connected to the suction side of the pump 28 is connected to the outlet of the pump 28, and the pump 28 no longer vents to the atmosphere. Therefore, as the vacuum toilets pans 12 are used, or if there are leaks in the suction side of the system 10, the pump 28 will pump the air that has entered the system into the lower chamber 26 to increase the pressure in the lower chamber 26. The collection plant 20 remains in the collect-and-pressurise state 80, with the upper chamber 24 filling with waste as the vacuum toilet pans 12 are operated, and with the pressure in the lower chamber 26 increasing, until the control unit 30 detects from pressure switch 70 that the pressure in the lower chamber 26 has reached +0.9 bar (gauge), whereupon the control unit 30 changes the collection plant 20 to the collect-and-discharge state 82.

Upon changing to the collect-and-discharge state 82, which is also shown in Figure 8, the motorised valves are set so that the valves 40,60 are open and the valves are 46,52,56 are closed. Accordingly, a vacuum is maintained in the upper chamber 24 so that the vacuum toilet pans 12 will still function. Furthermore, the pressure that was built up in the lower chamber during state 80, is used to force waste through the valve 40 and the discharge pipe 42 to the pillow tank 32, and the pump 28 continues to pump more air into the lower chamber 26.

Depending on the relative heights of the lower chamber 26 and the pillow tank 32 and other factors, the lower chamber 26 may or may not substantially empty itself in one operation.

Substantial emptying of the lower chamber 26 is detected by the float switch 66, and in response to this the control unit 30 changes the collection plant 20 back to state 78. However, if the pressure in the lower chamber 26 falls to +0.1 bar (gauge) as detected by the pressure switch without substantial emptying of the lower chamber 26 being detected by the float switch 66, the control unit 30 instead changes the collection plant 20 back to the collect-and-pressurise state 80. As a result, the lower chamber 26 is re-pressurised during the collect-and-pressurise state 80 before changing again to the collect-and-discharge state 82 to discharge waste from the lower chamber 26 to the pillow tank 32. After one or more attempts in the collect-and-discharge state 82 to empty the lower chamber 26, it will eventually be detected from the float switch 66 as substantially empty, whereupon the control unit 30 changes the collection plant 20 back to the collect-and-transfer state 78.

In addition to the principle states 78,80,82 described above, the collection plant 20 may also have one or more auxiliary states. For example, as shown in Figure 5, if in any of the principle states 78,80,82, the control unit 30 detects from the float switch 68 that the upper chamber 24 is substantially full, for example due to a blockage in the transfer pipe 44, the control unit 30 changes the collection plant 20 to a problem state 84 in which the pump 28 is switched off. An alarm warning may also be given.

It will be appreciated from the above that, by using a single pump 28, it is possible during normal operation to maintain a vacuum at the vacuum toilet pans 12 while periodically being able to discharge waste under pressure from the tank assembly 22 to the pillow tank 32.

Figure 9 shows how the sanitary system 10 may be packed away in a container 88 for storage and transportation. The container 88 is cuboidal and divided into four compartments 90A-D each having its own door 92A-D. Some of the compartments 90A-D are fitted with shelves (not shown). A first one of the compartments 90A contains the collection plant 20. A second one of the compartments 90B contains the vacuum toilet pans 12. A third one of the compartments 90C contains one or more lengths of flexible pipe 38, the pillow tank 32, a bedpan sluice interface valve, etc. The fourth compartment 90D contains the water tank assembly 14. Other items may also be included in the container 88, such as a generator, fuel and tools. In an embodiment of the invention, the container 88 has a footprint of about 2.3 m x 2.6 m and a height of about 2.2 m. The container is adapted so that it can be lifted by a fork-lift truck or using strops beneath a crane or helicopter.

Various modifications and developments may be made to the embodiment of the invention described above.

For example, as shown in Figure 10, the collection plant 20 may be provided with an additional collect-and-depressurise state 86 between the collect-and-discharge state 82 and the collect-and-transfer state 78, in which the valves 40,56 are open and the valves 46,52,60 are closed. Therefore, once the level of the waste in the lower chamber 26 has fallen to the lower float switch 66 (but the pressure in the lower chamber 26 has not necessarily fallen to +0.1 bar (gauge)), no more air is pumped into the lower chamber 26, but the discharge valve 40 stays open to allow any remaining waste in the lower chamber 26 to continue to flow to the pillow tank 32. Once the pressure in the lower chamber 26 falls to below, for example, +0.1 bar (gauge), as detected by a further pressure switch, the control unit 30 then changes the collection plant 20 to the next state, e.g. the collect-and-transfer state 78, or a collect-and-evacuate state 87 that will now be described.

The collect-and-evacuate state 87 may be provided between the collect-and-discharge state 82 (Figure 5) or the collect-and-depressurise state 86 (Figure 10) and the collect-and-transfer state 78, so that, immediately after the state 82 or 86, the transfer valve 46 remains closed until the pressure in the lower chamber 26 has been reduced to substantially the same pressure as in the upper chamber 24, as sensed by the pressure switch 72. This additional collect-and-evacuate state prevents a sudden rush of air from the lower chamber 26 to the upper chamber 24 at the end of the collect-and-discharge state 82 or collect-and-depressurise state 86.

Furthermore, although, in the collect-and-discharge state 82, the lower chamber 26 has been described above as being connected to the outlet of the pump 28 by the valve 60 being open and the valve 56 being closed, alternatively, in the collect-and-discharge state 82, the outlet of the pump 28 may be vented to atmosphere through the valve 56 and the lower chamber 26 may be isolated from the pump 28 by the valves 52,60.

Although two separate valves 56,60 have been described above for connecting the outlet of the pump 28 either to the vent pipe 58 or to the lower chamber 26, a single motorised diverter valve may instead be employed. Alternately, although two separate valves 52,60 have been described above for connecting the port 54 of the lower chamber 26 to the inlet or the outlet of the pump 28, a single motorised diverter valve may instead be employed. Moreover, the three valves 52,56,60 may alternatively be replaced by a single complex motorised valve which, in one state, connects the outlet of the pump 28 to the vent pipe 58 and connects the inlet of the pump 28 to the port 54 of the lower chamber 26 and, in its other state, connects the outlet of the pump 28 to the port 54 of the lower chamber 26.

Instead of employing different pressure switches 70,72 for detecting different pressures in the lower chamber 26, a single pressure transducer may be employed which sends to the control unit 30 a signal that varies progressively with varying pressure in the lower chamber 26.

Similarly, instead of employing different bistable float switches 64,66 for detecting different levels of waste in the lower chamber 26, a single level transducer may be employed which sends to the control unit 30 a signal that varies progressively with varying waste level in the lower chamber 26.

In this specification, the term "toilet-pan" is intended to cover, in addition to conventional vacuum toilet-pans, other devices such as sluice sinks used for the disposal of the contents of bed-pans.

It should be noted that the embodiment of the invention has been described above purely by way of example and that many other modifications and developments may be made thereto within the scope of the present invention. -Il-

Claims

(The reference nwnerals in the claims are not intended to limit the scope of the claims.) 1. A collection plant (20) for a sanitary system (10) employing at least one vacuum toilet pan (12), the collection plant employing an air pump (28), the pump serving both to maintain a vacuum at the vacuum toilet pan(s) so as to suck waste from the vacuum toilet pan(s) to the collection plant and, while maintaining the vacuum for the vacuum toilet pan(s), also intermittently to create a super-atmospheric pressure which is used to discharge the collected waste from the collection plant for subsequent treatment or disposal.
2. A collection plant as claimed in claim 1, wherein the plant includes an upper chamber (24) for connection to receive waste from the vacuum toilet pan(s), a lower chamber (26) generally below the upper chamber and having a discharge outlet (39), and a plurality of valves (40,46,52,56,60) and pipes interconnecting the chambers and the pump so that the plant is operable in: (i) a collect-and-transfer mode (78) in which the pump maintains a vacuum in both chambers, so that waste can be collected from the vacuum toilet pan(s) to the upper chamber, and waste can transfer from the upper chamber to the lower chamber; (ii) a collect-pressurise-and-discharge mode (80,82) in which the pump maintains a vacuum in the upper chamber so that waste can be collected from the vacuum toilet pan(s) to the upper chamber, waste in the upper chamber is isolated from the lower chamber, the pump pressurises the lower chamber, and waste can be discharged from the lower chamber through the discharge outlet utilising the pressure built up in the lower chamber.
3. A collection plant as claimed in claim 2, wherein at least some of the valves are motorised valves (40,46,52,56,60); and the plant further includes a plurality of sensors (64,66,70,72) and control means for controlling the motorised valves in dependence upon the sensors to change the plant from at least one of the modes to another of the modes automatically.
4. A collection plant as claimed in claim 3, wherein the motorised valves are controlled to perform at least one of the following functions: (i) to connect the upper chamber to the lower chamber when in the collect-and-transfer mode, but not when in the collect-pressurise-and discharge mode; (ii) to prevent discharge of waste from the lower chamber when in the collect-and-transfer mode; (iii) to connect the lower chamber to the inlet side of the pump when in the collect-and-transfer mode; (iv) to vent the outlet side of the pump to atmosphere when in the collect-and-transfer mode and (v) to connect the outlet side of the pump to the lower chamber at least part of the time when in the collect-pressurise-and-discharge mode.
5. A collection plant as claimed in claim 3 or 4, wherein the control means is arranged to respond to the sensors in at least one of the following ways: (i) when in the collect-and-transfer mode to change the plant to the collect-pressurise-and-discharge mode when the level of waste in the lower chamber is sensed to have risen to a particular level; and (ii) when in the collect-pressurise-and-discharge mode to change the plant directly or indirectly to the collect-and-transfer mode when the level of waste in the lower chamber is sensed to have fallen to a particular level.
6. A collection plant as claimed in any of claims 2 to 5, wherein the collect-pressurise-and-discharge mode includes: (1) a collect-and-pressurise sub-mode (80) in which the pump maintains a vacuum in the upper chamber so that waste can be collected from the vacuum toilet pan(s) to the upper chamber, waste in the upper chamber is isolated from the lower chamber, and the pump pressurises the lower chamber; and (ii) a collect-and-discharge sub-mode (82) in which the pump maintains a vacuum in the upper chamber so that waste can be collected from the vacuum toilet pan(s) to the upper chamber, waste in the upper chamber is isolated from the lower chamber, and waste can be discharged from the lower chamber through the discharge outlet utilising the pressure built up in the lower chamber during the collect-and-pressurise sub-mode.
7. A collection plant as claimed in claim 6 when directly or indirectly dependent on claim 3, wherein the motorised valves are controlled to perform at least one of the following functions: (i) to connect the outlet side of the pump to the lower chamber when in the collect-and-pressurise sub-mode; and (ii) to prevent discharge of waste from the lower chamber when in the collect-and-pressurise mode, but permit such discharge when in the collect-and-discharge mode.
8. A collection plant as claimed in claim 6 or 7 when directly or indirectly dependent on claim 3, wherein the control means is arranged to respond to the sensors in at least one of the following ways: (i) when in the collect-and-pressurise sub-mode to change the plant to the collect-and-discharge sub-mode when the pressure in the lower chamber is sensed to have risen to a particular level; and (ii) when in the collect-and-discharge sub-mode to change the plant to the collect-and-pressurise sub-mode when the pressure in the lower chamber is sensed to have fallen to a particular level.
9. A collection plant as claimed in any of claims 6 to 8, wherein the plant is operable in the collect-and-discharge sub-mode such that the pump does not pump air to the lower chamber.
10. A collection plant as claimed in any of claims 6 to 8, wherein the plant is operable in the collect-and-discharge sub-mode such that the pump does pump air to the lower chamber.
11. A collection plant as claimed in claim 10, wherein the plant is further operable in a collect-and-depressurise mode (86) in which the pump maintains a vacuum in the upper chamber so that waste can be collected from the vacuum toilet pan(s) to the upper chamber, waste in the upper chamber is isolated from the lower chamber, and waste can be discharged from the lower chamber through the discharge outlet utilising the pressure remaining in the lower chamber from the collect-and- discharge sub-mode.
12. A collection plant substantially as described with reference to the drawings.
13. A sanitary system (10) comprising at least one vacuum toilet pan (12) and a collection plant as claimed in any preceding claim for connection to the vacuum toilet pan(s).
14. A sanitary system as claimed in claim 13, further including at least one flexible pipe (38) for connecting the vacuum toilet pan(s) to the collection plant.
15. A sanitary system as claimed in claim 13 or 14, further including a flushing system (14,16,18) for flushing the vacuum toilet pan(s).
16. A sanitary system as claimed in any of claims 13 to 15, further including a tank (32) for receiving waste discharged by the collection plant.
17. A sanitary system as claimed in any of claims 13 to 16, in combination with a container for containing the sanitary system for transportation.
18. A sanitary system substantially as described with reference to the drawings.