Figure 1-12. Filter element (disassembled).
(c) Maintenance. There wiII come a time when the fiIter elements
become clogged by the constant build up of diatomite particles."
1 To clean or clear them, backwashing is necessary. The
equipment needs to be taken out of service for this process. Backwashing occurs when
compressed air, held by water pressure, is released as the air valve is opened. This
causes air pressure under the dome to suddenly be released. Air in the fiIter element
air traps expands rapidly which causes a "blast" that knocks diatomite and foreign
particles off the fiIter elements. The fiIter cakes are broken up too as the compressed
air, which was held by water pressure, is released from the cups. The released
compressed air causes water to reverse its flow, thereby breaking up the fiIter cakes.
2 Once the fiIter is backwashed and drained, it should be
washed/flushed. The fiItering unit is ready to be put back into operation after precoating
has been initiated and completed. The thickness of the precoat is about 1/16 inch.