Irrigation problems at Carpenter

PROBLEM: The irrigation station filters were plugging up within a minute or two of being backflushed.  Here is how it works: The system takes in water from irrigation canal, passes it thru a filter to trap debris, and clean water goes out to the orchard floor.
As debris in a filter increases, backflush is initiated. During backflush, the trapped debris which is flushed out.
But here, the filters are clogging within a minute of backflush.

OUR APPROACH: Disassembly of the filter station revealed no obvious problem. The plugging of the filters forced us to irrigate by opening only 2 of the 6 valves for each set instead of the normal 3. This reduced the flow through the filters to 1300 gpm instead of the normal 2100 gpm. 

Of course, the filters could handle the lower flow without a problem. The problem with irrigating this way is that it took 3 days to irrigate instead of only 2. Thus there would be a 50% increase in pumping costs and irrigation labor. 

CALLED IN HELP: We had the representative from the manufacturer (Netafim) out to evaluate the problem. He thought that cleaning the filtering elements (small grooved disks) with strong chlorine would correct the problem. After two tries, It did not. Perhaps, the filter elements had worn down and the resulting "mesh" was too fine for the canal water to pass through. The well water had no problem passing through the filters without causing plugging. 

PURCHASED NEW: Finally last week we purchased new elements and changed them. Went with an 80 mesh set of elements (it had been 120 mesh) which will be plenty small enough to prevent problems in the field and which will last much longer. 

The first irrigation with the new elements has gone very well, I sure hope the problem is corrected.