The present invention relates to a self-operated drum filter, comprising a pressure-proof body with its inlet, outlet and drain pipe as well as a rotating drum which is journalled inside the body and provided with a filter surface.

The invention relates further to a water filtration method, wherein water supplied from the inlet pipe is passed through the filter surface inside the drum and further to the outlet pipe.

In water-operated processes, it is often necessary to filter the water one way or another. One quite common filter is a circular drum with debris remaining on its periphery and being removed from time to time by rotat¬ ing the drum by means of a separate driving gear while the flushing is effected with a water stream created by a pump or pressure difference. This type of filter is usually expensive and quite complicated because of its driving gear.

An object of the invention is to eliminate the above problems and in order to accomplish this a filter of the invention is characterized in that the filter is fitted with a drain valve controlled by a pressure- difference switch, drum rotation retaining means, said drum being provided with a flange which, together with the gable of the body, builds an annular space which, by way of a slice in a connecting pipe, is in communic¬ ation with a space surrounding the drum.

A water filtration method of the invention is charac-

terized in that the cleaning of a filter is adapted to be self-operated in a manner that the pressure of intake water prevails in the annular space, whereby a pressure difference created as a result of a pressure loss occurring in the filter between the opposite sides of the flange together with a spring means causes the drum to push itself against retaining rings so as to prevent rotation of the drum until, as the pressure difference increases to a predetermined value, the drain valve opens by the action of the pressure- difference switch whereby, as some of the water passes into the drain pipe through said slice, pressure drops in the annular space and the direction of pressure dif¬ ference reverses with a result that the drum separates itself from the retaining rings, the drum beginning its rotation due to a turbine effect created on the vanes to effect the cleaning-of a filter surface.

The invention will now be described with reference made to the accompanying drawings, in which:

fig. 1 shows a longitudinal section of a drum filter of the invention, and

fig. 2 shows the drum filter of fig. 1 along section II-II.

As shown in figs. 1 - 2, the drum filter comprises a pressure-proof body 16 provided with an inlet pipe 1, an outlet pipe 2 and a drain pipe 11. Inside said body 16 is journalled a rotating drum 4 provided with a filter surface 3. The drum 4 is further provided with preferably inclined vanes 15 for providing a ro¬ tating motion and back-up vanes 5 as well as with a flange 14 which together with a gable 17 of body 16

builds an annular space 6. The annular space 6 is in communication with a space surrounding the drum by way of a slice 12 in a connecting pipe 13. The filter is further provided with means for retaining the rotating motion of drum 4 , comprising preferably a retaining ring 8 and 9 as well as a spring means 7. In addition, the filter is fitted with a drain valve 10, controlled by a pressure-difference switch and .whereby water can- discharge into a drain pipe 11 during the cleaning operation.

The drum filter operates so that the water coming in from inlet pipe 1 is passed through filter surface 3 inside drum 4 and further into outlet pipe 2. The pressure of intake water prevails by way of slice 12 of pipe 13 in annular space 6 whereby, as a result of a pressure loss occurring in the filter, a pressure difference develops between the opposite sides of flange 14 which together with spring means 7 causes ' drum 4 to push itself against retaining rings 8 , 9 to prevent rotation of the drum. As drum 4 is not rotat¬ ing, the circulation adopted by water is linearized by the action of back-up vanes 5 to provide a more uni¬ form flow into outlet pipe 2. As the filter surface becomes soiled, a pressure difference increases between the opposite sides of flange 14 until, when the press¬ ure difference reaches a predetermined value, a press¬ ure-difference switch causes the opening of drain valve 10, some of the water passing into drain pipe 11 through slice 12 and pressure of the water in annular space 6 decreasing and the direction of pressure difference re¬ versing with a result that drum 4 detaches itself from retaining rings 8, 9. Thus, drum 4 is set in rotation due to a turbine effect created on inclined vanes 15. The rotating motion is further intensified by a turbine

effect generated on back-up vanes 5 by the water flow¬ ing into outlet pipe 2. The cleaning of filter surf¬ ace 3 is based on a vigorous suction prevailing in slice 12 as well as on a centrifugal force created by rotating motion. As the pressure loss caused by filter surface 3 again decreases after a flushing operation, said drain valve 10 closes and, thus, the pressure in annular space 6- increases to be equal to the inlet pressure and the direction of pressure difference across flange 14 reverses and drum 4, assisted by spring means 7, sets against retaining rings 8 and 9 and is locked in its position again. Following this, the filter operates stationary until a pressure loss caused by soiling reaches again a preset value and the above-described flushing operation is repeated.

A drum filter of the invention can be installed in various water pipings in various sizes and provided with various pressures and various filter surfaces. A separate braking gear can also be used, especially in major units and when compressed air is available.

The above description only deals with one preferred embodiment which is by no means intended to limit the scope of protection as _. defined by the annexed claims.