Applications
IDEC SmartRelay Manual 251
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 in-
gress 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
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.
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
Courtesy of Steven Engineering, Inc. ● 230 Ryan Way, South San Francisco, CA 94080-6370 ● General Inquiries: (800) 670-4183 ● www.stevenengineering.com
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