The present invention relates to a liquid ring screw pump, including a housing with a suction inlet part and a pressure outlet part and within the housing rotatably provided Archimedes screw driven by a motor via a shaft.

Pumps of the above-mentioned kind are now commonly used in vacuum sewage systems onboard ships, aero planes and trains. However, such systems are also increasingly being used on land due to reduced water requirement and easy handling and treatment of waste water, as well as its flexibility as regards installation of piping and layout given by such systems.

The applicant of the present application introduced in 1987, cf. EP patent No. 0 287 350, for the first time the novel vacuum sewage system where the vacuum in the system was generated by means of a liquid ring screw pump of this kind 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 screw 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 present invention may, or may not include such grinder provided at the inlet end of the Archimedes screw rotor.

The suction inlet of the liquid ring screw pump according to the present invention includes a suction chamber with a particle trap where any un-wanted solid particles such as coins or other metal devices are trapped and thereby prevented form entering and damaging the grinder or screw. The suction chamber is provided with a lid or removable cover enabling access to the trap to remove trapped particles and inspection of the inlet and rotating components, i.e. the grinder and screw.

As the lid is commonly fastened to the suction chamber by means of a flange connection with screws and nuts the lid is cumbersome to remove and takes time open.

With the present invention is provided a solution which vastly reduces the time to connect and disconnect the lid and thereby reduces the time to perform maintenance, i. e. removal of trapped particles and doing inspections of the inlet and grinder etc. and which is much cheaper than the known flange type connection.

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 a liquid ring screw pump with a suction chamber front lid or cover according to the known (prior art) solution, Fig. 2 shows a liquid ring screw pump with a suction chamber front lid or cover according to the invention.

Fig. 3 shows an expanded view of the same liquid ring screw pump as is shown in Fig. 2.

Fig. 4 shows in larger scale a cross sectional view of the suction chamber with the lid or cover shown in Figs. 2 and 3.

Fig. 1 shows, as stated above, an example of a known liquid ring screw pump 1 including a housing 2 with a suction inlet part 4 (chamber) and a pressure outlet part 3 and within the housing rotatably provided Archimedes screw (not shown) driven by a motor 6 via a shaft (neither not shown). The inlet part 4 further includes a suction chamber which is provided with a front cover or lid 5. In the known solution as shown in Fig. 1 the cover is fastened to the suction chamber by means of a flange connection where the cover 5 is attached to a flange 7 on the suction chamber with a plurality of screw and nuts 14 in through-going holes. This known solution is secure, but quite cumbersome and time consuming to detach. The solution is as well expensive to manufacture due to the many holes to drill and number of screws and nuts being used.

Fig. 2 shows as well a liquid ring screw pump 1 , but with a front cover or lid 5 according to the invention. Figs. 3and 4, depicting respectively an expanded view and cross section, shows in more detail the simple and inventive cover solution according to the invention. As can be seen, the cover 5 is attached to the suction chamber 4 of the pump 1 by means of a locking ring 8 and with a sealing element in the form of an O-ring 9 provided between the cover 5 and chamber 4. The locking ring may be any ring capable of attaching the cover to the chamber, but preferably as shown in Fig. 3, some kind of twist locking arrangement where the ring is provided with outwardly protruding knobs or threads 10 corresponding to complementary inwardly protruding recesses or threads 1 1 on the chamber 4 and which by twisting of the ring 8 presses the outer edge of the cover 5 with the sealing element 9 towards a corresponding seat 12 on the chamber.

In the present case as shown in Fig. 3, the cover or lid 5 is transparent and made of a thermoplastic polymer such as Poly (methyl methacrylate) (PMMA), Polycarbonate marketed under the trade names Plexiglas ® and Lexan™ respectively, or Poly Vinyl Chloride (PVC). However, the cover 5 and the locking ring 8 may be made of any suitable material such as metal or suitable composite polymer.

In the present case as shown in the figures, the locking ring 8 is provided with transversal wing or holding element 13 that makes it easier to obtain a grip with the hand when twisting the ring on or off the cover (when mounting or de-mounting the cover). Such transversal wing or element merely represents an option and is not a requirement.

As the inlet part of the chamber 4 includes a rotating grinder, the locking ring 8 may preferably also be provided with a safety arrangement (not further shown) to avoid unintentional opening of the locking ring 8 and further avoiding injury to hand/fingers (caused by the grinder).