Backpressure is cause for concern because it can cause delamination of reverse osmosis membranes.
Delamination is a separation of the membrane from the backing material. This type of damage is caused by backpressure from the permeate side of the membrane and results in a loss of rejection.
Backpressure can be caused by restrictions in the line such as valves, resin beds, or elevated piping. It can also be caused by improper relief of product pressure in a product staged (double pass) RO system.
Figure 1 shows an example of severe backpressure damage where the pattern of the feedspacer (vexar) is clearly visible.
The bubbling of the membrane shown in Figure 2 is sometimes subtle and difficult to detect.
Figure 3 shows the membrane envelope, comprised of two sheets of membrane and one sheet of tricot (permeate carrier) between.
The yellow arrow is the tricot, the red arrow is the backing material and the blue arrows are the membrane that was pulled away from the backing material.
Delamination allowed easy separation of the membrane material from the backing material. This separation would not be possible on an undamaged element.
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