Because they're not externally adjustable, they don't need to be located close to the control panel. Depending on your application, you might want your salvaged pressure switch to operate at pressures that are different to its standard range. That's not hard to do if you have a washing machine pressure switch, as they are quite easy to modify.In standard form, turning the adjustment control typically allows the trip pressure to be set to detect water depths anywhere from 9cm to 20cm. But if you remove the adjustment.
The on-off cycle in the master timer should go on only for the set time (here it is 18 minutes). Once the master timer goes off, the cycle should stop. To achieve this, the outputs of both the timers are connected to NAND gate N1 (IC3), which gives a low output only when both the timers are giving high outputs.The output pin 3 of N1 is connected to relay RL1 via pnp transistor T1, so the relay energises only when the output from NAND gate N1 is low. As the mains 220V line is taken through relay RL1,the monitor turns off during the 3-second off period after the set time of 10 seconds is over.