The invention relates to a filter, especially to self-cleaning filters.

US 2015174513 discloses for example a self-cleaning filter. This filter has a permeable cylindrical wall, wherein a fluid is fed to the inside of the cylindrical wall and wherein filtrate permeates through the wall and exits the filter.

The residue remains at the inner wall of the cylindrical wall. To remove this residue a scraper or cleaning disc is provided, which can be moved along the length of the cylindrical wall and scrapes off the residue and conveys it to one end of the cylindrical wall, where the residue is discharged into a purge chamber.

When the purge chamber is full with residue, a closable purge port is opened, such that a part of the fluid, which is fed to the filter, can flow through the purge chamber and can flow out through the purge port. This flow of fluid through the purge chamber takes along the residue and the purge chamber is emptied.

A self-cleaning filter is designed to handle a specified flow rate. If a higher flow rate is required, it is possible to arrange a number of filters in parallel.

However, not in all situations sufficient installation space is available to arrange separate filters and arrange the required piping for parallel feeding of the filters.

GB 229270 discloses a filter in which a number of filter elements are arranged in one housing to reduce space. A single scraper is arranged on the outside of all the filter elements. In order to operate the scraper, one needs to open the filter housing and manually move the scraper up and down and manually remove the residue. Due to the arrangement of the scraper on the outside, the pressure of the fluid is build up between the housing wall and the filter and thus not in the filter itself. Especially, when the filter is not cleaned sufficiently by the scraper this could lead to an increase of the pressure in the housing.

So, clearly the filter according to GB 229270 is not suited for continuous filter operation.

Accordingly, it is an object to provide a filter, in which the above mentioned disadvantages are reduced or even removed. This object is achieved according to the invention with a filter comprising:

- a housing with a first divider wall and a second divider wall spaced apart from the first divider wall, the housing wall and the first divider wall forming an inlet chamber, the housing wall, the first and second divider wall forming an outlet chamber and the housing wall and the second divider wall forming a purge chamber;

- an inlet port connected to the inlet chamber;

- an outlet port connected to the outlet chamber;

- a closable purge port connected to the purge chamber;

- at least two longitudinal filter elements extending from the first to the second divider wall, each filter element having a permeable circumferential wall enveloping the longitudinal axis and having a scraper arranged on the inside of and in contact with the permeable circumferential wall, wherein the scraper is movable along the longitudinal axis between a first end and a second end of the filter element, wherein the first end debouches in the inlet chamber and wherein the second end debouches in the purge chamber;

- at least one baffle plate arranged in the purge chamber between the second ends of the at least two filter elements, wherein the at least one baffle plate extends in longitudinal direction of the filter elements for separating at least partially the flow from each second end to the purge port.

By arranging at least two filter elements in one housing reduces the required installation space and only single piping is required to connect the filter via the inlet port and outlet port.

Furthermore, a purge chamber is provided such that the filter can be used continuously and the permeable circumferential wall can be cleaned with the scraper when desired even during the cleaning phase.

The use of a single purge chamber however requires baffle plates to avoid that when one filter element is cleaned by its scraper, the residue flows directly in one of the other filter elements. The baffle plates ensure, that the second ends of the filter elements are separated from each other and a flow of residue from one filter element via the second end into another filter element is avoided.

In order to empty the purge chamber, the purge port is opened such that fluid flows from the first end of each filter element to the second filter element into the purge chamber and is discharged via the purge port taking the residue along.

In a preferred embodiment of the filter according to the invention, the at least one baffle plate extends from the second divider wall to the inner surface of the housing forming separate purge chambers for each filter element and wherein the purge port debouches in each of the separate purge chambers.

By having the at least one baffle plate extending over the full width of the purge chamber, separate purge chambers are created for each filter element, which separate purge chambers are only connected to each other via the purge port. This minimizes the chance of any residue flowing from one filter element into another filter element.

In a further embodiment of the filter according to the invention, each filter element comprises a guide rod arranged on the longitudinal axis of the filter element, wherein the scraper is guided over the guide rod.

Preferably, a magnetic piston is slidably arranged in the guide rod and the scrapper is magnetically coupled to the piston.

The magnetic piston allows for the movement of the piston and therefore of the coupled scraper by use of air pressure or fluid pressure. Simply by supplying on one side of the piston air pressure, the piston can be moved inside of the guide rod, which will also move the scraper being magnetically coupled to the piston.

In yet another embodiment of the filter according to the invention the housing comprises a lid for accessing the inlet chamber. The lid allows for opening the housing to provide large maintenance, such as exchange of filter elements.

These and other features of the invention will be elucidated in conjunction with the accompanying drawings.

Figure 1 shows a cross-sectional view of an embodiment of a filter according to the invention.

Figure 2 shows a cross-sectional view of the purge chamber of the embodiment of figure 1.

Figure 1 shows an embodiment of a filter 1 according to the invention. The filter 1 has a housing 2 with a lid 3 for accessing the housing 2.

A first divider wall 4 and a parallel second divider wall 5 are arranged inside of the housing 2. As a result an inlet chamber 6, an outlet chamber 7 and a purge chamber 8 are formed. The inlet port 9 is arranged to the housing 2, such that the inlet port 9 is in direct contact with the inlet chamber 6, while the outlet port 10 is arranged to be in direct contact with the outlet chamber 7. A purge port 11 with a valve 12 is connected to the purge chamber 8.

filter elements with a permeable cylindrical wall 13, 14 extend between the first divider wall 4 and the second divider wall 5. A fluid F, which is fed via the inlet port 9 into the inflow chamber 6 flows via the first ends of the filter elements into the space enveloped by the cylindrical walls 13, 14. The fluid F flows through the permeable cylindrical wall 13, 14 leaving residue behind, whereafter the filtered fluid Ff can flow out of the filter 1 via the outlet port 10.

Each filter element has furthermore a guide rod 15, 16 along which a scraper 17, 18 can be moved. With the scrapers 17, 18 the residue present on the inside of the cylindrical wall 13, 14 can be scraped via the second end of the filters elements into the purge chamber 8.

Figure 2 shows a cross-sectional view of the purge chamber 8. As can be seen in figure 2, four second ends of filter elements 13, 14, 19, 20 debouch into the purge chamber 8.

Each second end of the filter elements 13, 14, 19, 20 is separated by a baffle plates 21, 22 dividing the purge chamber 8 in separate purge chambers 23, 24, 25, 26, such that any residue being scraped into the purge chamber 8 does not directly flow into one of the filter elements 13, 14, 19, 20.

The purge port 11 has overlap with each of the separate purge chambers 23, 24, 25, 26 such that when the valve 12 of the purge port is opened, the fluid F can flow through the filter elements 13, 14, 19, 20 through the separate purge chambers 23, 24, 25, 26 taking the residue along and discharging it via the purge port 11.