3-20. BACKWASH TIMER. (MECHANICAL)
a. General. The backwash timer automatically starts and ends the different stages of the backwash cycle of
the multimedia filter. The timer provides the capacity to begin the backwash cycle at a preset time of day. This
paragraph describes the disassembly, cleaning, inspection, repair, reassembly, testing, and adjustment of
presetting dial on the backwash timer.
b. Removal. If necessary, remove the backwash timer assembly from the multimedia filter assembly in
accordance with paragraph 256.
c. Timer Mechanism Disassembly. (Figure 318, Sheet 1 of 2)
The backwash timer is a delicate piece of equipment. It can be
damaged if dirt or grease gets into the mechanism. Before
beginning disassembly of timer assembly, make sure work space
is clean and uncluttered. Clean timer assembly before taking it
Identify and tag all wires before disconnecting them for ease of
(1) Open timer case (l), (figure 3-18, sheet 1 of 2), lift latch (2), and remove timer mechanism assembly
(17) from timer case (1).
(2) Identify, tag, and disconnect electrical wires from terminal block (1 5), micro switch (5), four micro
switches (8), timer motor (25), and timer controller assembly.
(3) Remove two screws (7), two washers (6), two insulators (4), and micro switch (5), from switch base
plate assembly (3).
(4) Remove two nuts (10) and two washers (11) from two screws (12) through four micro switches (8)
(5) Remove four switches (8) and five insulators (9) from two screws (12) and switch base plate assembly
(6) Remove spring (35) and two nuts (13) from two screws (14) through switch base plate assembly (3),
timer mechanism assembly (17), and cover (34).
(7) Remove two screws (14), switch base plate assembly (3), timer mechanism (17), and cover (34),