Filtration system for liquids with suspended particles

Electro-erosion liquid 24 is filtered as it flows from inlet 11 to outlet 12 of filter 10. Periodically valve 6 is adjusted to reverse the flow through the filter, the backwash liquid flowing via conduit 42 to settling tank 9. Then forward flow is restored to rinse the filter, the liquid still flowing from the filter to tank 9. Finally normal filtration is restored, but the first filtered liquid is recycled through conduit 13' to dirty liquid tank 7 before flow is diverted to normal outlet 13. Tank 9 is divided by adjustable wall 40 with lower apertures 41. During backwashing the flow carries solids through the apertures to settle in chamber 92. Chamber 91 collects relatively clean rinsing liquid which is recycled via valve m, to tank 7. Level sensors O1 to O3 in chamber 91 control the various steps in the cycle.