Telescoping of a membrane is caused by excessive differentials between the feed pressure and the concentrate pressure.
The maximum pressure differential for a single 40” long membrane is 10 psi. When this pressure is exceed, damage to the membrane and its materials of construction can occur.
Consequences of Telescoping:
- Damage to the fiberglass outer wrapping allows water to flow on the outside of the element. This will reduce crossflow across the membrane surface and increase the fouling potential.
- If the feed spacer (vexar) moves within the membrane area, it can scratch the membrane surface and cause permanent damage.
- Glue lines can be stressed and fail.
- Flow patterns will be disrupted, resulting in channeling over the membrane surface and uneven fouling.
- The membrane crease will be stressed. Failure can occur at these points near the permeate tube.
Prevention:
- Monitor pressure differentials across the entire system as well as across each array.
- If the fiberglass is damaged, repair with vinyl tape or place the brine seals on the opposite end if the fiberglass and ATD are not damaged on that end.
- Clean the system before pressures exceed 10 psi per membrane element and correct any excessive fouling problems.
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