The reliable RO membrane is an important component of each RO system. Each membrane element requires a special RO membrane housing. The purpose of the RO membrane housing is to create the proper conditions for the RO membrane to operate efficiently producing clean water under the applied pressure. The RO membrane housing distributes the flow of feed water into concentrate and permeate water. It isolates the “permeate” (clean) water from the feed water and the concentrate. There are two main types of reverse osmosis membrane elements: spiral wound and hollow fiber membrane elements. The spiral wound elements are mostly used to produce drinking water while hollow fiber is used in the treatment of waste water and other special cases. The spiral wound RO membrane elements are made from packets of RO membrane flat sheets, permeate and concentrate spacers. Those packets are rolled around a core tube to form cylindrical shaped membrane element that can fit into a tubular RO membrane housing.
Reverse osmosis membranes vary in diameter and in length. The membrane housing should match the size of the membrane element. In the USA the most popular diameters for the RO membranes and housings are 2.5”, 4” and 8”. Commercial RO systems usually use 2.5” and 4” membrane housings while 8” housings are used in industrial RO systems.
The RO membrane housing for commercial RO systems can accommodate the following membrane lengths: 14”, 21”, and 40”. Sometimes, one housing is used to hold 2, 3 or 4 commercial 4” membrane elements. Industrial 8” reverse osmosis systems are usually designed around multi-membrane housings. The number of membrane elements per housing may be up to eight.
Membrane housings have different pressure ratings. Based on the TDS in the feed water, the operation pressure of reverse osmosis systems vary between 80 and 1000 psi. Each RO membrane housing manufacturer classifies membrane housings differently. However, the most common pressure ratings are: 150 psi, 225 psi, 300, psi, 450 psi, 600 psi, 1000 psi and 1200 psi. Tap water RO systems usually utilize 150, 225 and 300 psi membrane housings. The 450 and 600 psi ro membrane housings are used in brackish water RO systems and 1000 and 1200 psi housings in sea water RO systems.