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Operation & maintenance manual, Drum filter HDF 12/16/20/24 -series
6.2.2 Operating mode HAND – continuous rotation/washing
Operation with continuous drum rotation and backwash. In this mode, the water level inside the
drum is kept virtually constant. The level sensor and the automatic control system are disabled
when the HAND operating mode is selected.
6.2.3 Operating mode AUTO – automatic level control
With level control enabled, drum rotation and the backwash pump are activated when the water
level inside the drum reaches the level sensor. If an external wash water supply is used, the level
sensor can control a solenoid valve instead of a pump. The water level inside the drum will vary
when AUTO mode has been selected. The water level is at its lowest immediately after a back-
wash cycle and then rises until it reaches the level sensor. If a constant water level is required
inside the drum, the filter should be run continuously (HAND mode).
6.2.4 Adjusting the level sensor
Place the level sensor 50–100 mm below the overflow wall. The optimal placement depends on
the turbulence of the water surface (see Figure 6.4).
NB.
Prior to service, read section 2.7 (Safety instruc-
tions).
6.2.5 Adjusting delay time
A time relay/logic module is used to delay the back-
wash stop after the water level has dropped below
the level sensor. The time relay/logic module is pre-
set so that the drum is backwashed for one revo-
lution after the water level has dropped below the
level sensor. In certain applications it can be necessary to increase the time that the filter is back-
washed after the water level has dropped below the level sensor to prevent future clogging.
NB.
Prior to service, read section 2.7 (Safety instructions).
6.2.6 Setting the level relay
The sensitivity of the level sensor can be set from MIN to MAX at the level relay’s upper adjust-
ment screw (see F in Figure 6.2). The lower adjustment screw must always point to the side mar-
ked EMPTY. On this side there are three different sensitivity ranges, H, S and L. If appropriate
sensitivity cannot be set using the selected sensitivity range, another sensitivity range can be
chosen:
⊲ For water with high conductivity (low resistance), choose setting L.
⊲ For water with low conductivity (high resistance), choose setting H.
Figure 6.4 Adjusting the level sensor
