Shimming - It is normal to have some movement of the RO membrane elements within their pressure vessel housings. This occurs because the pressure drop across the elements can cause them to compress. Fouling or high flow rates can also result in significant movement, mostly when the reverse osmosis system starts-up. When it shuts down, the elements will then relax.

This movement can cause rubbing against the inter-connector O-Rings, particularly in the lead end elements. Over time, this can cause them to abrade and possibly break. In caseS of severe pressure drops, O-Rings can be completely dislodged and blow out of their slots.

The potential for this movement of the membrane elements should be minimized by ensuring that the elements fit tightly within their pressure vessel. Any unwanted gaps should be eliminated using shims.

Shims are slices of plastic piping that have an inside diameter that just fits over the outside of an end connector; usually the end connector between the lead end element and the vessel end cap. Enough shims should be installed so that replacing the end cap in its vessel meets with some resistance.

Technical support and advice

Reverse Osmosis Chemicals International work closely with a diverse range of global organisations, intelligently combining advanced treatment technologies with practical solutions to resolve complex issues. If you have a project you would like to discuss, or you require technical support and assistance; or if you simply have a question about our reverse osmosis technology solutions please contact one of our specialist advisors using our Technical Support page or call us on +44 (0) 330 223 31 31.