Emergency Water Leak Shut-off

[AGUS]

A neighbor of mine recently had a drain pipe for a water softener type device plug up and force waste water up to the kitchen sink which overflowed into 2 upstairs rooms and ruined ceiling tile in the basement and also carpeting.

I have quite often thought that an alarm system that would warn of water leak problems in the basement would be a good thing to have. One problem with only an alarm is that it does little good if it is not heard at night or the problem occurs when no one is at home.

So I recently built a emergency pump shut-off circuit that will limit spilled water to what is in the pressure tank (4 gallons or less).




The circuit uses a 30 amp DPDT relay which is normally in the inactivated state, so there is no power drain until a problem occurs.



The sensor part of the circuit uses a low voltage relay powered by a MOSFET transistor. This is powered by 4 AA cells to get ~6 volts. I measured imperceptible drain on these batteries (no reading on micro-ammeter) so batteries should last a long time (> 2 years).



Sensors are simply 2 wires stripped and tinned and set in a plastic block. I have them at every sink and the main utility room in the basement. The MOSFET is a readily available inexpensive one (2N7000) and is required to drive the 6 volt relay. Besides the 2 relays and MOSFET there is a 100K ohm 1/4 watt resistor to bias the FET to keep it in OFF state and a FLYBACK diode to protect the FET from reverse current when the relay turns off. Most any small signal diode would work.



Once the circuit is tripped by a leak, it latches and turns on an alarm signal.



To reset the circuit after being tripped, simply turn off then on the breaker for the pump.

Of course this is only good for well water systems in its present configuration but I don't suppose it would be very difficult to make a shut-off valve for a city water system.



Thanks for looking
Aaron