This water pressure switch connects to the output of a water tank pump, and switches the pump motor on until a certain pressure is reached in the diaphragm chamber. The pressure is held in the diaphragm chamber and downstream by a one way valve on the inlet.
The pressure is measured by a diaphragm with a spring pushing against it. When the pressure reaches the desired level the diaphragm will begin to be pushed outwards by the water pressure. When the diaphragm moves outwards, a rod connected to it will also move outwards. This rod is solid plastic as far as I can tell and is not magnetic. This rod slides in a blind hole cut into the inside of a cylinder protruding out of the diaphragm chamber.
The circuit board has a hole in it and sits around this protruding cylinder in the diaphragm chamber (refer to the images if this description is not clear, and i'm sure it isn't, even i'm having trouble reading it
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).
The part I am having trouble with is that I do not know how the circuit board is sensing the position of the rod within the cylinder in the diaphragm chamber.
The input power is switched to pass directly to the motor controller by a 24v dc coil input relay, I'm assuming this 24v dc is generated by a diode bridge and voltage divider because the only chip on the board is a quad schmitt trigger which i assume is used for hysteresis on the pressure sensing.
I tried replacing the relay as it had burn marks on the contacts but that didn't work. I have a whole replacement unit now so I'm only trying to understand the sensing mechanism now.
The only suspects I can see are the two raised components (marked RD? on the circuit board, I couldn't find any info on that marking) sitting on what looks to be custom plastic mounts, in the same light blue as the other custom plastic. I'm having trouble identifying what these components are (temp sensors?), they appear to be coated in a clear material. But I don't see how temp sensors could sense the rod position.
The only wild theory I can think of is that one of these components is acting as a transmitter and the other as a receiver and the position of the rod changes the transmission efficiency in a detectable way.
I'm sure it is something simpler that I just don't know about and cannot easily search for. I'm also sure someone who does know would know what's going on straight away so thanks in advance for any help.