The liquid enters the filter and first passes the coarse screen (red) from the outside to the inside.
Now
the liquid flows to inside the fine screen. The fine screen (blue) consists
of a support body with 316 woven stainless steel meshwire. Water flows through
the fine screen from the inside to the outside, leaving behind particulate matter
on the woven meshwire.
Particles trapped by the fine screen begin to form a filter cake. The filter cake gradually causes a pressure differential between the inlet and outlet of the filter. The automatic cleaning cycle starts at a pre-determined pressure differential.
The longer filter models have a piston; at the beginning of the back wash, the piston moves forward. Now the flushing valve opens. Since the drain is at atmospheric pressure, a low pressure path is created through the dirt collector and lower compartment. The debris that is "vacuumed-off" the fine screen travels through the dirt collector and lower compartment to the drain.
During back washing the nozzles move along the complete filter area, thus cleaning the whole fine screen very efficiently. The complete backwash cycle takes 5 - 15 seconds, depending on the kind of filter. Normal filtration continuous during back washing.