Dec 28, 2000

Changing Reverse Osmosis Membranes

Changing membranes in pressure vessels is easy with the proper tools. Here is how we do it.

To open a PVC pressure vessel, first remove any pins holding one end plug in place. (Note: many fiberglass pressure vessels use a snap ring to hold the plug in place. Properly -sized snap ring pliers should be used to safely remove the snap ring.) Next, remove the fittings from the plug.

Thread a nipple and tee into the feed or concentrate port long enough to extend past the end of the pressure vessel. Apply a coating of glycerin to the inside and rim of the pressure vessel from the plug to the end so the plug will slide out more easily. Pry off the plug using a pry bar. We either use a ball joint separator, also called a "pickle fork," which is an automotive tool, or a slide hammer. Remove the fittings used to remove the plug.

Next, remove the membrane from the pressure vessel, noting which side the brine seal is on. Insert the new membrane with the brine seal on the feed side of the pressure vessel. Replace any damaged O-rings. Lubricate the plug with glycerin. Tap the plug securely into place using a piece of wood and a rubber mallet. Replace any pins to hold the plug in place. Reattach the fittings to the pin.

With a new membrane, flush all permeate and concentrate to drain for 30 minutes at low pressure to flush out the preservative.

About the author

Dorothy Korszen, P.E., J.D., is the executive vice president of Environmental Products USA, Inc., a manufacturer of membrane systems and pressure vessels.