About reverse osmosis back pressure generation and avoidance

What is Back Pressure       
In reverse osmosis water treatment, back pressure refers to a situation where the pressure on the product water side is greater than the pressure on the feed water side. A rolled membrane element resembles a long envelope-shaped membrane pocket with the open side bonded to a product water center tube containing an opening. A plurality of membrane pockets are wound onto the same product center so that a flow of feed water passes over the outside of the membrane, and under feed water pressure, fresh water is allowed to flow through the membrane into the membrane pockets and then converge into the product water center tube.        

In order to facilitate the flow of product water inside the membrane pockets, a fabric support layer for product water conduction is sandwiched inside the envelope-shaped membrane pockets; in order to enable the feed water to flow uniformly over the surface of the membrane pockets and to give the water flow disturbance, a spacer layer is sandwiched between the membrane pockets and the membrane pockets in the feed water channel. 

   The three sides of the membrane pocket are bonded together with a binder, if the pressure on the product water side is greater than the pressure on the feed water side, then these bonding lines will rupture and result in the loss of the desalination rate of the membrane element or a significant reduction in the membrane element, so from the point of view of safety considerations, reverse osmosis system can not exist back pressure.        As the reverse osmosis membrane filtration is driven by pressure, there is no back pressure in normal operation, but if the system is normal or fault shutdown, the valve is improperly set or opened and closed, then there may be back pressure, so must be properly handled to solve the problem of back pressure.

How is back pressure generated? How to avoid back pressure?

     General reverse osmosis membrane related technical manuals are back pressure limit parameters, assuming that the maximum back pressure that the reverse osmosis membrane can withstand is 0.1MPa, that is, about 1bar pressure, which is equivalent to the pressure generated by 10 meters of water column. Reverse osmosis in the shutdown, the existence of water in the water production pipe will inevitably produce a certain pressure on the reverse osmosis membrane water production side, and the higher the water production pipe to climb, the greater the pressure, and if the water production pipe to climb more than 10 meters, then the water production side of the water production of the back pressure will be enough to cause damage to the membrane. Therefore, the reverse osmosis design process should be provided for 8 meters for the production of water pipe the highest climbing height, and in the production of water pipe on the installation of check valves to prevent the production of water in the water pipe to produce pressure. There may be times when the check valve is not strict or the water production pipe climbing height must be made high, in this case, can be taken in the water production pipe check valve after the installation of the method of evacuation pipe to prevent the back pressure.