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The membranes need to be cleaned only when feed pressure begins to rise due to fouling or
the product quality degrades. The primary causes of fouling are biological growth and scal-
ing. Biological growth occurs when the system is left unused without flushing or pickling.
Fouling from mineral scaling will form when the feed water is high "hard" or high in car-
bonates. Very small "colloidal metal" and metal oxide particles can also plug the pores in
the membrane. Monitor the product salinity and feed pressure for higher than normal read-
ings for the existing conditions. Other conditions can cause high pressure such as cold feed
water or clogged filters. Low product flow is usually due to low voltage, damaged feed
pump or hydraulic intensifier. Look for all other causes before cleaning the membrane.
Membrane life can be shortened by excessive cleaning.
There are two types of cleaners: acid and alkaline. The acid cleaner (Storage-3) will remove
mineral scaling. The alkaline cleaner (Storage-2) is used to remove biological by-products,
oil, and dirt particles that get past the prefilters. If membrane performance is reduced and it
has not been "pickled" recently, cleaning with both chemicals is recommended. The acid
cleaner should be used first. Colloidal Metals and Metal Oxides are very difficult to re-
move. If the membrane fails to respond to both cleanings, this is an indication of another
problem with the system, or that it is time to replace the membrane. Contact W.S. Darley &
Company before removing a membrane.
Membrane Cleaning
For normal cleaning, the Storage-3 Acid Cleaning Compound is used first, then the Storage-2
Alkaline Cleaning Compound. If known bio-fouling is present, the Storage-2 may be used first.
Using hot water if possible, up to 120° (45C) is recommended as it greatly enhances the ability
of the cleaners to do their jobs.
If the history of the system is unknown or it has been left "unpickled" for an extended length of
time and biological growth is present, it is recommended that the system is cleaned with Stor-
age-2, using an alternate source of unchlorinated fresh water before the system is run under
pressure. A simple test can be performed to see if biological growth has occurred. Before run-
ning the system, remove the prefilter and examine its condition. If the housing is full of smelly
discolored water, the system was not properly stored. Install a clean prefilter if it was bad. Next
check the membrane. Attach the feed and brine service hoses and lead them to a bucket of clean
de-chlorinated water. Open the pressure relief valve one turn, and manually run the system for
30 seconds. Examine the brine water: if it's discolored and smells bad, perform an Storage-2
cleaning with an alternate source of unchlorinated water before running the system pressurized.
If the brine is fairly clean, the system can be purged, run normally, and checked for perfor-
mance. Clean the membranes only if performance is reduced.
Heating the water is preferable. One way to do this is to find a camp stove and use a large stain-
less steel pot to heat the solution in. The cleaning solution throughout the system will heat as it
circulates in and out of the pot. An alternative is to heat the one or two gallons of initial water to
120° on the main stove before mixing in the cleaner and circulating it into the system. Periodi-
cally stop and reheat the solution.
The Membranes
17
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