IDEC FL1E SmartRelay - Manual (Page 308)

Applications
294 IDEC SmartRelay Manual 
8.7.1 Requirements for a control system of a service
water pump
• Service water must be available at all times. In case of
emergency, the control system must automatically switch
over to drinking water supply.
• When switching over to the drinking water supply, the
ingress of rainwater into the drinking water system must
be prevented.
• The service water pump may not be switched on if the
reservoir has run low of rainwater (dry-run protection).
8.7.2 Previous solution
K1 K2
K3
S1
K3
S4 K3
L1
N
K4
S3 K4 p< K2
S3 S2
Y1
Auxiliary circuit
Pump Tracking
time Dry-run 
protection
Drinking water
supply line
The pump and a solenoid valve are controlled by means of a
pressure switch and 3 float switches, which are installed in
the rainwater reservoir. The pump must be switched on
when the pressure level in the boiler drops below minimum.
After the operating pressure is reached, the pump is
switched off again after a tracking time of a few seconds has
expired. The tracking time prevents oscillation of the water
pump if water is drawn off over a longer period of time.