disclosed are spiral - wound membrane cartridge constructions for use in ultrafiltration and reverse - osmosis separation equipment , each of which include a feed layer , a membrane layer and a permeate carrier layer . by using a feed layer in the form of a channel material having a plurality of parallel ribs extending in an axial direction , interconnected by a matrix of smaller filaments which may be generally perpendicular thereto , this construction advantageously reduces resistance to liquid frlow axially through the cartridge , registering only very low pressure drops . such cartridges of 40 to 70 inches in length and 8 inches in diameter may be employed in series , even within a single outer casing or pressure vessel . such constructions are especially useful in separating liquids having high levels of particulate contamination using ultrafiltration membranes where clogging of the cartridge is a common problem and also in concentrating solutions of fairly viscous water - soluble polymers .