Background of the invention

The present invention refers to a method for effecting rinsing of an inverted siphon, which forms part of a sewer, and a device for performing the method.

Sewers and the like, which shall pass under a water course or another similar obstacle are often provided with a so called inverted siphon, i.e. a conduit which mainly in U-shape extends below the inclination line of the sewer. The inverted siphon is continuously filled with water and if the water velocity therethrough is low there _^ is a big risk that it will be gradually silted up. Self-rinsing of inverted siphons is obtained at a certain flow velocity which is named the rinsing velocity and is dependent on the dimensions of the conduit. At the smallest inverted siphons which are generally used a water volume of about 16 l/s is required for reaching the rinsing velo¬ city and this volume corresponds to the sewage volume from 300-400 small houses during the maximum hour.

In cases where the built-up areas are smaller, which is very common, it is thus not possible to reach the cri¬ teria which are necessary for obtaining self-rinsing inver¬ ted siphons,* and- it is thereby used conventional sewage pumping stations for giving the water a sufficient velo¬ city through the inverted siphon to achieve rinsing. Such a pumping station is however comparatively expensive both to build and to run and it furthermore gives rise to pro¬ blems as it at stoppage will spill over and contaminate the receiving body of water which has often a very low discharge.

The purpose and most important features of the invention

The purpose of the present invention is to offer a simple and reliable method of effecting rinsing of the inverted siphon when the head of the discharge is low and at flow volumes unsufficient for without, the use of a sewage pum¬ ping station and without encountering the disadvantages me tioned hereabove and this is according to the invention achieved by arranging upstreams of the inverted siphon a fluid reservoir haying a reservoir volume which at least corresponds to the volume of the required rinsing distance, and by temporarily and shortly, some time per twenty-four hours, giving the fluid content of the reservoir a flow velocity through the inverted siphon, which at least corresponds to the required rinsing velocity for carrying away sludge which has accumulated in the inverted siphon-

The invention also incorporates a device for accomplishing the method and this device is mainly characterized by a fluid reservoir arranged upstream of the inverted siphon, and having a reservoir volume between normal pressure head curve and τhe least inclined pressure head curve required for maintaining the required rinsing velocity and means adapted to cause the content of the fluid reservoir to be emptied through the inverted siphon during a short time and at a velocity at least corresponding to the required rinsing velocity.

Description of the drawings

The invention will hereinafter be further described with reference to the embodiment shown in the accompanying drawings.

Figure 1 shows in a cross-section a schematic device for performing the method according to the invention,

Figure 2 is a schematic detail view of a part of the de¬ vice according to the invention, and

Figure 3 shows a schematic coupling diagram for an em¬ bodiment of the driving and control system of the device.

Description of the preferred embodiment

In figure 1 is shown in cross section a sewer 1 having a pressure head curve 2 and which sewer at passage below a crossing water stream 3 is equipped with an inverted siphon h . The waste water flows through the conduit at a speed and at a pressure head curve, which is determined by the approaching flow and by the inverted siphons ma¬ terial, appearance and dimension.

Upstream of the inverted siphon k there is arranged a fluid reservoir 5, which has such a volume that it corre¬ sponds to a water volume, which is sufficient for giving the fluid during a sufficiently long time, commonly about 1 minute, rinsing velocity i.e. about 1 meter/sec , which for the smallest conduit area corresponds to about .6 l/s. In order to give the fluid in the reservoir 5 a sufficient speed through the inverted siphon h there is in the present case a mammoth pump 6 connected as a part of the inverted siphon. The mammoth pump is driven and controlled by equip¬ ment located in a space 7 _» which is preferably heated and insulated and which as can be further seen from figure 2, i.a. encloses a compressor 8 and a tank 9 for compressed air which is charged by the compressor. In the space ~ there is furthermore arranged not shown electric equip¬ ment, control equipment, valves etc.

The control equipment of the device incorporates a con¬ trol member adapted at proper occasions to start the com¬ pressor 8, which thereby will charge the compressed air tank 9 with compressed air and thereafter again will be

closed down by the control member when a sufficient vo¬ lume of compressed air has been supplied to the tank. The tank 9 is connected to the mammoth pump 6 via a feed con¬ duit 10, which has a controlable valve placed therein, which valve is preferably controlled by the impulses from said control member and which thereby preferably is closed when the compressor 8 is started and which is opened when the compressor is closed down. Between the valve and the mammoth pump there is arranged a reduction valve for maintaining the air pressure to the mammoth pump constant during the entire rinse pumping process.

Vhen the stop valve opens the compressed air in the tank will empty through the jet tube of the mammoth pump, whereby the pressure head curve at the jet tube will drop in correspondance to the head of the discharge of the mammo-fch pump thus that the pressure conditions necessary for the rinse pumping action are obtained. The head of discharge of the mammoth pump is equal to the difference in altitude between pressure head curves 2 and 12.

At the very starting moment a maximum inclined pressure head curve 11 is obtained. The inclination of the pressure head curve will thereafter be gradually reduced as the reservoir is emptied until the least inclined pressure head curve 12 required for maintaining the required rin¬ sing velocity is reached. Vhen this condition has been reached the compressed air in the tank 9 is also used up and the mammoth pump 6 terminates to pump and will in¬ stead act as a part of the inverted siphon. Vhen the rinse pumping process thus has terminated the reservoir 5 will again automatically be filled up by the approaching fluid, whereby it will contain a required fluid volume when the next rinse pumping process is started. Vhen the reservoir 5 has been filled the fluid will flow in the ordinary manner from the sewer 1 upstream of the inverted siphon

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4 through this and further through the sewer la down¬ stream of the inverted siphon. Pressure head curve 2 is then again at hand. In the sewer 1a downstream of the inverted siphon 4 there is arranged an aerating tube 13, which will aerate the tube system.

In figure 3 is shown in a schematic coupling diagram a preferred driving and control equipment for the device according to the embodiment of the invention shown in figures 1 and 2.

As can be seen from the figure the equipment incorporates a time switch 14 which is connected to an electric current source and which forms the main part of the control means and is adapted at certain intervals, e,g_ each twelfth or twent -fourth hour to close a switch 15, whereby a first relay 16 operates and starts a motor 17 _. which runs the compressor 8, which will thereby press air into the com¬ pressed air tank 9. Vhen the switch 15 is closed a second relay 18 is simultaneously acted upon which second relay switches a magnetic valve 19 from a position, in which the feed conduit 10 from the tank 9 to the jet tube of the mammoth pump is held open to an alternative position in which it closes the conduit 10. Vhen the time switches again, opens the switch 15, after a certain time, which corresponds to time required for charging the pressure air tank 9 the relays 16 and 18 will both release, where¬ by the compressor 8 is closed down and the magnetic valve is switched over to allow the air in the tank 9 to pass to the mammoth pump via a reduction valve 20.

Although the invention hereinbefore has been shown and described as a preferred embodiment it is to be under¬ stood that a lot of modifications are possible within the scope of the claims attached to this application.

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The mammoth pump 6 can thus be substituted by other com¬ ponents for giving the fluid such a high speed that the rinsing velocity is reached and exceeded. As an example on such a component can be mentioned pneumatic driving or it is also possible to place the reservoir so high that the fluid therein can reach rinsing velocity by aid of the self-pressure when the conduit is open. The driving power supplied is hereby used for lifting the fluid up to the reservoir. Another detail solution is to drive the fluid by aid of compressed air acting inside the re¬ servoir.

It is furthermore possible to govern the driving means and the valves in other ways then by the time switch, e.g. by sensing pressure, velocity and/or level.

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