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