Technical Field

The invention relates to a method of determining the amount of waste deposited on filter cloths of a drum filter rotatably suspended on a shaft and to a device for carrying out said method in which the drum is rotatably mounted on at least two suspen¬ sion-type supporting members embracing a shaft seated on the stationary frame of the drum filter.

Background of the Invention

Drum filters contain a rotatably mounted drum fitted on its circumference with filter cloths and with two face holes out of which through one, an inlet hole, soiled liquid, as a rule water, is led inside, while through the other, the outlet hole, impurities are let out, for instance by means of an off-take trough. The lower part of the drum filter is immersed in the filtered liquid, and the level of the soiled liquid inside the drum of the drum filter is higher than the level of the filtered liquid outside the drum filter.

In the heretofore known devices, the determining of the waste amount deposited on the filter cloth of a drum filter is carried out by devices recording the level heights inside and outside the drum filter, for instance by means of float-operated switching on and off systems, or by means of electronic, pres¬ sure or optical feelers disadvantageous in that they

are apt easily to take up the waste contained in the soiled liquid with the ensuing deterioration of the functional accuracy. _.

The rotation of the drum of the drum filter results in undulation of the liquid levels which is another cause of incorrect working of the level height feelers. In addition to the limited reliability of the function, other drawbacks of the known devices consist in their complicated design, high production costs, and poor response to the changes in the level height .

Disclosure of the Invention

The above specified drawbacks are removed by a method of determining the amount of waste deposited on filter cloths of the drum of a drum filter rotatab¬ ly suspended on a shaft whose principle consists in that there are recorded the changes in the total mass (weight) of the drum of the drum filter which correspond to the changes in the amount of waste deposited on filter cloths and to the changes in the height of the level of soiled liquid^ inside the drum of the drum filter.

The device for carrying out the method according to the invention comprises a drum rotatably suspended on at least two suspension-type supporting members embracing a shaft seated on the stationary frame of the drum filter, and its principle consists in that at least one force recorder is provided for between the shaft and the stationary frame of the drum filter.

In a preferred embodiment, the force recorder is seated under the shaft at the place where the shaft is embraced by the supporting member.

The shaft can be mounted on a lever swingingly seated on the stationary frame of the drum filter, the force recorder being seated between the free arm of the lever and the stationary frame of the drum filter.

The advantage of the method according to the invention consists in the accuracy of determining the level height difference inside and outside the drum of the drum filter and, in particular, high reliability regardless of the amount of waste deposit¬ ed on the feelers. The advantage of the device accord¬ ing to the invention consists in its simple design due to its location outside the inner space of the drum.

Brief Description of the Drawing

An example of embodiment of a device for carrying out the method according to the invention is schemati¬ cally represented in the accompanying drawing showing the face of the drum of the drum filter.

Modes for Carrying Out the Invention

Drum filters are used for filtering soiled liquids, in particular water. The drum filter comprises a drum J_ consisting in a well-known manner of two faces with horizontal axis interconnected by not shown reinforcing members, with not shown filter cloths mounted along the circumference

of the drum. The filter cloths are mounted in a known manner which is not the subject of this Patent Appli¬ cation .

The lower part of the drum J^ of the drum filter is immersed in the (ready-)filtered liquid. The soiled liquid is in a well-known manner led into the inner space of the drum J^ of the drum filter, and its level height is superior to the level height of the (ready)- filtered liquid. The level height difference provides for the hydrostatic pressure responsible for the filtering process going on.

The drum _1_ of the drum filter is rotatably mounted on suspension-type supporting members 2 _^ em¬ bracing a shaft k_ , in the shown example of embodiment a roller _ mounted on the shaft h_. In the shown exam¬ ple of embodiment, the shaft 4_ is rotatably seated in the body of a single-arm lever 5_ swingingly mounted on a stationary frame j6 of the drum filter. Between the arm end of the single-arm lever _5 and the stationary frame _ is situated a force recorder 7_ at a distance from the fulcrum of the single-arm lever _5 _^ greater than the shaft 4_. In the shown example of embodiment, the suspension-type supporting members 2_ are two in number and they embrace the circumference of the drum J^ of the drum filter. However, the number of the suspension-type supporting members can be more than two. The terminal (outward) suspension- type members 2_ can embrace well-known not represented supporting rings fixed to the faces of the drum 1_ of the drum filter. At least one of the suspension- type supporting members 2_ is coupled with a not shown well-known driving device controlled by a not shown well-known control unit which is by means of a not

shown line connected with the force recorder 7_.

In another embodiment, the single-arm lever 5_ can be replaced by a double-arm lever.

On the stationary frame 6 _^ of the drum filter is rotatably mounted a stabilizing roller 8_ touching the circumference of the drum _1_ of the drum filter and stabilizing its position during the rotation of the drum j^, in particular in its initial and final phases of rotation, i.e., in the start and stop-motion phases in which impacts occur. More than one piece of the stabilizing roller 8 _^ can be used.

The suspension-type supporting members 2_ ^can embrace the shaft 4_ directly, with no rollers 3_ inter¬ posed between them, and the force recorders 7_ may be in other embodiments located between the shaft _ and the stationary frame (^ of the drum filter, at least one force recorder 1_ °f ^an known type being obligatory for each drum 1_. Also, the shaft 4_ can be suspended on the force recorder 7_ at due place.

In the shown example of embodiment, the shaft _ is made as a through shaft throughout the length of the drum j_. However, it can also be made as a divided shaft seated in a well-known way on the stati¬ onary frame b_ of the drum JL_ of the drum filter.

Soiled liquid led into the inner space of the drum _1_ °f t-h _* ³ drum filter passes during the filtering process through the filtering cloths arranged on the circumference of the drum 1_ and on which deposits the waste while the (ready-)filtered liquid is col¬ lected in the space outside the drum l_ and is in

a well-known manner led away from there. The hydrostatic pressure due to the level height difference inside and outside the drum _1_ keeps the filtering process going on. The waste continuously depositing on the filter cloths impairs their permea¬ bility for the liquid, and the level inside the drum J^ rises. When the amount of the waste deposited on the filter cloths is excessive, it is necessary to turn the drum _1_ a bit; at this, a large part of the waste falls into a well-known waste off-take trough which is in a well-known manner located in the upper part of the inner space of the drum 1_ of the drum filter. After the turning movement of the drum, into the filtering process enter the non-deposited filter cloths, and the filtering process goes on with the original or only slightly decreased intensity.

The turning movement is imparted to the drum JL_ by a command given by a well-known not shown control unit to a well-known not shown drive device. The control unit receives signals coming from the force recorder 7_ recording the mass (weight) of the drum _1_ of the drum filter. The changes in the mass of the drum \_ of the drum filter due both to the deposi¬ tion of the filter cloths and to the rising level of the soiled liquid inside the drum _1_ of the drum filter are evaluated by the control unit which gives out a signal for turning the drum J_ when preset values have been reached. In the same manner is watched also the maximum level of soiled liquid in the drum 1_ of the drum filter corresponding to the complete obstruction of filter cloths of the drum 1_ of the drum filter, and at which the control unit sends out a signal for putting the drum filter out of opera¬ tion and for exchanging the filter cloths.

The monitoring of the increase in the total mass of the drum _1_ of the drum filter permits to check the changes in the amount of waste deposited on the filter cloths of the drum 1 _^ and thus to control the action of the drum filter.