Bollfilter, Type-6.48: Functional description of the automatic filter

The automatic filter is used to filter particles from media in order to protect the downstream parts of the plant such as bearings, journals and shafts in the motor from damaging impurities in the oil.
The automatic filter is suitable for filtering liquid media (oils) with an operating pressure of at least 3 bar.
It works with permanent medium backflushing. The backflushed liquid is fed back into the circulation tank or oil tank.

Filtration stage
Figure: Filtration Stage

1 Filter candle inlet- N1
2 Connecting pipe outlet- N2
3 Protective sieve
4 Turbine
The medium being filtered passes through the inlet flange and turbine to the bottom end of the filter candles. A partial current is fed via the connecting pipe to the top end of the filter candles.
This means that the medium flows through the filter candles at both ends, from the inside to the outside, and in the process larger particles of dirt are held back on the inside of the filter candles.
The filtered medium then proceeds to the filter outlet through the protective sieve.

Backflushing stage
Figure: Backflushing Stage

1 Rotary indicator
7 Bottom sieve plate
2 Inspection glass
8 Cog wheel
3 Top flushing arm
9 Worm gear pair
4 Top sieve plate
10 Turbine
5 Coupling pipe
11 Bottom flushing arm N1 Filter inlet
6 Filter candle N2 Filter outlet
N3 Flushing oil outlet

The flow energy drives the turbine which is integrated in the inlet flange. The worm gear pair and cog wheel reduce high speed turbine speed to low speed to rotate the flushing arm.
The individual filter candles are connected alternately to the atmosphere and the flushing bush and nozzle (optional) by the continuously rotating flushing arms.
By this a pressure gradient, which has a particularly efficient cleaning effect on the filter candles, is produced. This connection is established alternately by the bottom and top flushing arm. In each case, the opposite side of the filter candles is closed at the same time. This also changes the direction of flow of the medium through the filter candle which in turn increases the cleaning effect.
The turbulent flow created in the longitudinal direction of the filter candle (cross flow backflushing) and the counterflow backflushing through the filter material lead to a particularly enduring backflushing effect.
The combination of cross-flow backflushing and counterflow backflushing causes the pressure loss in the filter to remain constant.
Overflow valves
Figure: Overflow Valves

1 Filter candle N1 Filter inlet
2 Overflow valve N2 Filter outlet
3 Differential pressure monitoring
N3 Flushing oil outlet
4 Protective sieve

If, for any reasons, the filter candles are no longer sufficiently cleaned (i.e. dirty), the overflow valves open automatically from a defined differential pressure level and the medium is partly filtered through the protective sieve only (emergency mode).
However, before this status occurs, a differential pressure signal (first contact) is issued by the optional differential pressure monitoring systems. The cause must then be localized and remedied.
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