Continuous automatic filters, in which filtering and flushing stages alternate, are used, for example in diesel motors for filtering fuel or lubricant. Filtering is used to remove the principally solid impurities wearing the motor.

Filtering apparatuses applicable for the above-mentioned purpose are known, in which the filtering is conducted alternately in two or several parallel filtering cham- bers, controlled by a rotating spindle acting as a valve. The cleaning of the filtering chambers is performed by backflushing between the filtering stages. An apparatus of this type is disclosed in the patent publication US 4 256 583.

As filtering is again adopted after the flushing stage in the filtering room, it is ad- vantageous to fill the filtering room slowly and controllably with liquid before initi- ating the filtering. The intention is to get air removed from the filtering room as completely as possible, as its mixing with the filtered fuel or lubricating oil would be detrimental.

An automatic filter is available at the markets, in which the filtering room is pre- filled with clean filtered liquid led into the room from an opening arranged in the spindle controlling the parallel filtering rooms. The upper end of the filtering room in the same filter is provided with a float, which closes the exit route for air, as the room has been filled with liquid. Filtering is then initiated in the said filtering room from the inlet assembly in the spindle through the jacket of the filtering element as a flow-through into the outlet assembly in the spindle.

A drawback in the said known solution is that the filling assembly in the spindle is always open in the direction of the filtering room, which prevents the opening of the room for changing the filtering elements or for other servicing measures. Opening the filtering room would result in the discharge of the liquid under pressure out of

the room. It would be difficult to arrange the filling assembly as closing, and it would require that the structure of the spindle be changed.

The object of the present invention is to provide a solution for the said problem so that the filling assembly for prefilling the filtering room with liquid does not pre- vent the opening of the filtering room for servicing measures. It is characteristic of the filtering apparatus of the invention that the filling assembly is formed by a fill- ing channel led through the casing of the filtering room, the channel being provided with a valve for closing the channel upon opening the filtering room.

The filling channel arranged according to the invention for prefilling the filtering room is advantageous especially in the filtering apparatus in accordance with the applicant's previous patent application FI 982113, of the three filtering units of which controlled with a common valve organ, two are meant to operate alternately in the actual filtering process, at the same time as the third unit forms a reserve unit, into which the flow to be filtered is led during the service of the two units men- tioned first. The performance of such an apparatus requires that the unit may be opened, for example, for changing the filtering elements without separate measures as soon as the filtering flow has been transferred to the reserve unit.

According to an advantageous embodiment of the invention, the filtering room is restricted by a stationary casing, which is provided with an opening cover, and the valve is provided with a spring, which is arranged to achieve the closing of the valve as the cover is opened. In other words, as the cover of the filtering room is opened, the valve will automatically close the filling channel.

The said co-operation of the cover and valve may be achieved, for example, with a bar affecting the compression spring in the valve, the bar moving from its place pushed by the spring as the cover is opened so that the spring simultaneously closes the valve. At the same time, the bar may advantageously be arranged as a support for the filtering element or elements in the filtering room.

It has to be possible for the air remaining in the room after the flushing stage to leave the room during the prefilling of the filtering room through the filling channel, for which purpose the room may be provided with an air vent beginning from its upper end. Closing the channel after the filtering room has been filled with liquid may be achieved, for example, with the help of a float raised by the liquid. An axle formed from a tube may advantageously be used as the air vent, the axle working simultaneously as a support for the filtering elements arranged around it.

Alternatively, air may be arranged to be discharged from the filtering room into a separate air container, into which air is compressed, pushed by the liquid filling the room. The air container may be separated from the centre of the filtering room and formed as part of an axial element, which from its lower end affects the compres- sion spring of the valve in the filling channel so that the element makes the valve to close as it moves from its place.

The invention is next described in more detail with the help of examples, referring to the enclosed drawings, in which Figure 1 is an elevation view of a filtering apparatus of the invention ; and Figure 2 is a similar view of a second filtering apparatus of the invention.

The filtering apparatus according to Fig. 1, which is suitable, for example, for an automatic filter of a fuel or lubricant system in a diesel motor, comprises according to the figure a base 1 and two parallel filtering units 2, on the alternating use of which the operation of the apparatus is principally based. The filtering units 2 are controlled with a spindle 3 so that, as the filtering is running in the one unit, the second unit is being cleaned by backflushing with pressurised air, whereafter the operations are switched between the units. The apparatus further includes a third fil- tering unit controlled by the same spindle 3, which is left behind the spindle in the figure, and which operates as a reserve unit during the service of the units 2 seen in the figure. Of these parts, the structure and operation of the apparatus corresponds to those disclosed in the patent application FI 982113 or the international applica- tion PCT/FI99/00798, these applications being with this reference incorporated as part of this specification.

In Fig. 1, the leftmost of the two filtering units 2 is in the filtering stage, in which the travel of the flow to be filtered through the unit is indicated with arrows. The spindle 3 guides the flow to be filtered from the inlet channel (not shown) common for the units 2 through the inlet assembly 4 into the filtering room 5, which com- prises eight cylindrical, candle-shaped filtering elements 6 arranged as a ring around the central axle 7 formed from the tube of the filtering room so that the axle oper- ates as a support for the filtering elements. During filtering, the filtering unit 5 is en- tirely filled with the liquid to be filtered. The liquid to be filtered is infiltrated into the elements through the jackets manufactured of filtering material, such as metal or plastic net of the filtering elements 6 in the filtering room 5, and is discharged as cleaned through the open lower ends of the elements into the outlet assembly 8 of

the spindle 3, from which the flow is directed into the discharge channel (not shown) common for the filtering units 2.

In the left filtering unit 2 in Fig. 1, the inlet channel 9 for flushing air is closed by the valve 10 during the filtering stage. Upon transferring to the flushing stage fol- lowing the filtering stage, the valve 10 is opened so that pressurised air flowing along the air channel 9 from the base 1 pushes the liquid in the filtering room 5 ahead into the reject channel (not shown), controlled by the reject spindle common for the units 2, whereafter the air flow continues along the same route so that the fil- tering elements 6 in the room are backflushed with air. As the flushing stage ends, the valve 10 closes the air channel 9.

After the flushing stage, before the filtering is initiated, prefilling of the room with clean liquid is performed in the filtering room. In Fig. 1, the right filtering unit 2 is shown in this prefilling stage. The liquid is filtered, clean liquid from the flow outlet assembly 8; the filling channel 11 feeding the liquid into the filtering room travels part of the way in the spindle 3 and part of the way in drillings formed into the sta- tionary casing 12 of the filtering unit. Only the last mentioned are completely shown in Figure 1. The valve 13 with the compression spring 14 and with the verti- cally movable closing organ 15 on top of it is formed into the filling channel 11 in- side the casing 12. The filtering unit 2 is provided with the opening cover 16 of the filtering room 5 so that the tubular central axle 7 of the room keeps the valve open, stressed against the compression spring between the closing organ 15 and the cover 16. The filling flow can thus travel along the channel 11 to the lower end of the fil- tering room, through which it gradually fills the filtering room as a slow and con- trolled flow and pushes air present in the same room ahead into the air vent formed by the axle 7 and leading downwards from the upper end of the room. In the upper end of the filtering room 5, the annular float 17 is arranged around the axle 7, the float being raised by the liquid during the filling of the room so that the float achieves the closing of the air vent. The filtering room 5 is now substantially emp- tied from air, and the filtering stage may be initiated by rotating the spindle 3 so that its inlet and outlet assemblies 4,8 are connected to the respective assemblies in the room and allow the flow to be filtered to travel between the room and the filtering elements 6 in it. The rotation of the spindle 3 simultaneously interrupts the filtering stage in the second filtering unit 2 in the apparatus.

For changing the filtering elements 6 in the filtering units 2 seen in Fig. 1, the cover 16 of the unit is opened so that the compression spring 14 of the valve 13 can raise the closing organ 15 and axle 7 so that the valve closes the prefilling channel 11 for

liquid. The axle 7 with the filtering elements 6 it supports may now be freely lifted from the filtering room 5 and returned back after the elements have been regener- ated or replaced with new ones. The change of filtering elements or other servicing measures are preferably made as the filtering is directed to the reserve unit in the said apparatus.

The filtering apparatus in Fig. 2 differs from the one in Fig. 1 in that that during the prefilling of the filtering room, air remaining in the room after the flushing is not pushed through the air vent 7 out of the apparatus, but the air container 18 is ar- ranged in the centre of the filtering elements 5 in the room, into which air in the room is compressed through the axial channel 19. In the figure, the right filtering unit 2 is shown in the starting stage of prefilling with liquid, similarly to Fig. 1, so that the liquid level in the filtering room 5 is rising. In this embodiment, the appara- tus does not comprise floats 17 according to Fig. 1, but after reaching the upper end of the room, the filling liquid flows forward into the axial connecting channel 19 and fills also the lower end of the air container 18 so that the situation is what it seen in the leftmost filtering unit in Fig. 2. With the help of the liquid, air is thus compressed into the air container 18 to the pressure corresponding to the normal operating pressure of the apparatus.

The left filtering unit 2 in Fig. 2 is shown in the filtering stage, which is performed as is explained above in connection of Fig. 1. Air compressed into the air container 18 is kept in the container during the filtering without being mixed with the liquid to be filtered.

As the filtering stage ends, the spindle 3 is rotated so that the flow assemblies 4,8 into the left filtering unit are closed. For flushing, connection is opened from the fil- tering room 5 into the reject channel so that air compressed in the air container 18 is able to push the liquid out of the filtering room with its pressure. The backflushing of the filtering elements 6 is performed with pressurised air directed from the opened flushing air channel 9.

In the embodiment according to Fig. 2, the cylindrical air container 18 has been constructed as a support for the filtering elements 6 surrounding it in a similar way as the tubular axle 7 in Figure 1. Thus, the air container 18 is part of the axial ele- ment, the lower end of which leans against the closing element 15 pressing the spring 14 of the valve 13 and which, upon opening the cover 16 of the filtering unit, bounces upwards due to the effect of the spring 14 and may thus be lifted out of the filtering room 5 for changing the filtering elements or for some other similar servic-

ing measures. The spring 14 and the closing element 15 close the prefilling channel 11 for the liquid similarly as in the embodiment according to Fig. 1.

It is obvious for one skilled in the art that the various forms of embodiment of the invention are not limited to the examples shown above, but they may vary within the enclosed claims.