This inserted layer, with a thickness that can vary according to needs, has the role of protecting the activated carbon bed against the abrasive action of {HEAD ~ the grains} of {TAIL ~ sand} during filtering or washing 
of
This inserted layer , with a thickness that can vary according to needs , has the role of protecting the activated carbon bed against the abrasive action of { HEAD ~ the grains } of { TAIL ~ sand } during filtering or washing
OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH HEAD HEAD HEAD HEAD HEAD HEAD REL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH