FULLY AUTOMATIC TANK FILLING SYSTEM

FULLY AUTOMATIC TANK FILLING SYSTEM

Here a simple circuit which can be used for controlling the water level in both the single tank or the combined overhead / sump tank systems automatically .It switches on the motor pump when the water level in the overhead tank falls to a pre-set minimum level (P1) and switches off the pump when the water level reaches the maximum pre-set level (p2) in the overhead tank .It automatically switches off the motor when the sump runs dry or the motor fails or the pump is unable to pump water from the sump .This unit gives one visible indication for motor running and another indication for pump failure (or dried up sump) for attending to its failure.

This unit can be powered from the domestic AC mains and consumes very little power .A 4-core cable (three for probes and one for earth wire),is to be drawn from the unit to the overhead tank .Two CMOS CD4011 ICs (quad 2-input NAND gates) are used.

In fig-1when the water level in the overhead tank goes below probes P1, P2 becomes ‘high’ making the out put of flip flop high .This sequence enables the transistor to conduct and operate the relay .The relay operation extends supply to the motor and water starts filling in the tank .As soon as the water touches probe P2, P2 becomes ‘low’ .This reset the flip flop which de-energizes the relay and stops the motor .It remains in the same state till the water level goes below P1.

For those who want to stop the motor if there is no water in the sump is not able to pump the water up, and want to get an indication or alarm to attend to the failure, the circuit will be used as shown in fig-2. The out put of gate N1b, in addition to driving the motor also triggers the monostable. The period of the monostable is set according to the motor is ‘on’ .After this period, the out put of the monostable becomes high .Even at the instant , if the water does not come out of the pump because there is no water in the sump or the motor fails, probe-P3, which is just beneath the mouth of the filling pump at the overhead tank, remains high, turning the out put of the gate N2b low and, turns the diode NAND gate low thus turning off the relay and supply to the motor .The out put of gate N2d drives the LED, indicating this failure .This LED remains lit and the supply to the motor remains cut as long as the circuit is not reset manually after attending to the failure.

Parts List

Semiconductors

IC1, IC2 -CD4011

T1, T2 -SL 100

D1, D2 -1N 4007

D3, D4 -LED

Resistors

R1-R4 -1 M

R5, R6 -10 K

R7-R9 -1 K

Capacitors

C1 -0.1 mF

C2 -10 mF

RELAY -12 V, 100 E