The present invention relates to a vacuum sewage system and improvement of such system, including one or more vacuum generator/s with integrated macerator, in particular liquid ring screw pump/s with integrated macerator, and further including beyond the vacuum generator/s one or more tubular collectors or suction pipelines connected to the vacuum generator/s and one or more toilets, urinals, grey water sinks etc. connected to the suction pipeline/s. Vacuum sewage systems of the above-mentioned kind are commonly known and dominating in connection with the use onboard ships, aero planes and trains. However, on land such systems are also increasingly used and the background for such increased use is primarily the reduced use of water and easy handling and treatment of waste water, as well as the flexible system as regards installation of the pipes given by such system.

The applicant of the present application introduced in 1987, cf. EP patent No. 0 287 350, a novel vacuum sewage system where the vacuum in the system is generated by means of a liquid ring screw pump and where the pump is used as well to discharge the sewage from a vacuum tank or the like to which it is connected. EP patent No. 0 454 794, also filed by the applicant, further shows a revolutionary improvement of a vacuum sewage system where the liquid ring pump is provided with a grinder or macerator and is connected directly with the suction pipe of the system, whereby vacuum is generated in the sewage suction pipe and sewage is discharged directly from the system by means of the pump.

The known vacuum sewage solution as shown in the EP patent No. 0 454 794 is provided with a check valve (non-return valve) at the suction side of the pump to close off the suction pipe and thereby maintain the vacuum level in the suction pipe when the vacuum pump comes to a halt after having obtained the required vacuum level.

A disadvantage with the above-mentioned known system is, however, that the check valve easily becomes ineffective, clogged or does not function properly due to build-up of material (paper, excrements, or cloth material etc.) on the valve body or seat from the sewage. A water spray nozzle is therefore usually provided in connection with the valve housing to rinse the check valve, i.e. its seat and valve body. Failure of the check valve results in reduced vacuum or loss of vacuum and increased maintenance.

With the present invention is provided a solution which vastly reduces the above- mentioned disadvantages and problems and thereby reduces maintenance of the vacuum system.

The invention is characterized by the features as defined in the attached independent claim 1. Advantageous embodiments of the invention are further defined in the attached dependent claims 2 - 4.

The invention will be further described in the following by way of examples and with reference to the drawings where: Fig. 1 shows, as an example, a schematic sketch of a vacuum sewage system, partly in large scale and partly in small scale, with a vacuum generator and check valve, or non-return valve according to a known (prior art) solution,

Fig. 2 shows a vacuum sewage system as shown in Fig. 1 , but with a check valve solution according to the present invention.

Fig. 3 shows part of a vacuum sewage system as shown in Fig. 2, but with an alternative solution.

Fig. 1 shows, as stated above, an example of vacuum sewage system 1 including, depicted in larger scale, a vacuum generator in the form of a liquid ring screw pump 2 with an inlet 5 and outlet 6, the pump being driven by a motor 3 via a shaft (not shown) and provided with a macerator 4, the pump further, depicted in small scale, being connected to a sewage pipeline or collectorl O arriving from toilets 7 and urinals 8 etc.. At the inlet end 5 of the pump 2 is provided a check valve 9 which closes off the sewage pipeline 10 to maintain the vacuum in the pipeline when the pump 2 comes to a halt. A vacuum system of this kind briefly works as follows: When flushing a toilet 7 or urinal 8, the vacuum (sub-pressure) in the sewage pipeline will drop and based on signal from a vacuum detector (not further shown) the vacuum pump 2 will immediately start to evacuate fluid, i.e. gas (air) and sewage from the pipeline and thereby create vacuum in the pipeline. The check valve 9 is now open due to the suction by the pump. When the required vacuum level (set in advance) is reached the vacuum detector will cut the signal to the pump and the pump will stop. At the same time the check valve 9 will close to maintain the vacuum in the pipeline until a toilet or urinal is flushed and the operation will be repeated.

The check valve 9 shown in Fig. 1 is of the tilting disc type with a spring loaded disc or flap body 1 1 designed to rest against and open I relation to a valve seat 12. The spring effect on the disc 1 1 keeps the valve closed when not being subjected to fluid flowing through it (the fluid flow opens the valve).

For completeness sake Fig. 1 shows a system where the vacuum pump 2 at the outlet end is provided with an arrangement for liquid priming of the pump in the form of a tank 13 for supply of liquid to the pump to maintain the liquid seal (i.e. priming of the pump) during idle running, cf. the applicants own EP patent No. 1397595.

The disadvantage with this solution is, as formerly stated, that the sewage passing through the valve contains larger particles which may stick to the valve body or seat and which in turn may cause leakage and eventually clogging of the valve. Leakage results in increased pumping capacity requirement and thereby reduced efficiency for the system, and as well increased maintenance.

Fig. 2 shows the same system as shown in Fig. 1 but with a solution according to the invention where a check valve 15 is provided at the outlet end 6 of the pump 2, or more precisely in this case at the outlet end of the liquid tank 13. The check valve in this example is of the ball type comprising a ball 16 provided in a valve housing 17, the ball being designed to rest against a complimentary valve seat 18 by the force of gravity. The major improvement and advantage with this solution is that the sewage passes through the grinder before flowing through the check valve, whereby the large particles following the sewage is ground to very small particles that easily passes through the valve without sticking to the valve body or valve seat. Thereby leakage is avoided, the capacity is maintained and maintenance is reduced. Extensive testing under common use of the inventive solution as defined in the claims has proven that the sticking and clogging is no more occurring.

Providing the check valve in a vacuum sewage system on the outlet end of the pump was initially thought of as a problem since the pump would be subjected to vacuum causing leakage from the outside atmosphere between the pump shaft and shaft sealing (not further shown). With the measures taken to improve the shaft sealing, such problem has not been observed. Fig. 3 shows an embodiment of the system as shown in Figs. 1 and 2, but where the pump 2 is shown without the tank 13 (shown in Figs. 1 and 2) and where instead the priming of the pump is accomplished with the supply of priming water directly to the pump housing through a priming water supply pipe (not shown). The check valve 21 is provided directly in connection with the outlet 6 of the pump 2. Further, in this example, the check valve 21 is a flap valve of the same type as shown in Fig. 1 . As is apparent from this embodiment the vacuum system as described in the present application and defined in the attached claims, may not be restricted to the embodiment as shown in Fig. 2, but may be based on a liquid ring screw pump solution without priming water tank. Besides the check valve may be of any suitable type and be made of any suitable material.