Demands On The Control System For A Rainwater Pump; Previous Solution - Siemens LOGO! Series Manual

Applications
5.6.1 Demands on the control system for a rainwater
pump
S
The water must be available at all times. Whenever necessary, the con-
troller must switch automatically to drinking water.
S
When the switch to drinking water takes place, no rainwater must get
into the drinking water system.
S
If there is not enough water in the rainwater tank, the pump cannot be
switched on (run-dry protection).

5.6.2 Previous solution

Auxiliary circuit
L1
K3
K2
K1
N
Pump
The pump and a solenoid valve are controlled by a pressure switch and 3
float switches in the rainwater tank. The pump must be switched on when
the pressure goes below the minimum permitted. Once the operating pres-
sure is reached, the pump is switched off again after an after-run time of a
few seconds. The after-run time prevents the water pump from constantly
being switched on and off if the water is drawn for any length of time.
98
S3
S1 p<
S4
K2 K3
After-run Run-dry
protection
time
S2
K3 S3 K4
K4 Y1
Pure water
supply
EWA 4NEB 712 6006-02
LOGO! manual