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Washing machines stop filling with water when air pressure in a hose reaches a certain point.

The bottom of the hose is attached to the bottom of the tub. On older machines the top of the hose is attached to a diaphragm that pushes against a switch. As the water in the tub rises so does the water in the hose, which pushes the air in the hose against the diaphragm which in turn pushes against a switch which stops the filling.

But on new washers the top of the hose is attached to a solid state sensor mounted on a circuit board which has no user adjustments.

Is there a way to adjust the air pressure in the hose? The washing machine has several water level settings so the sensor still has to detect different pressure levels. IOW it cannot be set for a fixed pressure. For example how would you lower the pressure by 10% all the time in order for each setting to fill 10% higher?

Is there any reasonably easy way to accomplish this?

Thanks for any suggestions.

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    $\begingroup$ Raise the sensor? $\endgroup$
    – Transistor
    Commented Aug 7, 2022 at 14:45
  • $\begingroup$ the washing machine may have a calibration mode $\endgroup$
    – jsotola
    Commented Aug 8, 2022 at 7:29
  • $\begingroup$ Increase the length of the hose. You will need more water to get the same overpressure. $\endgroup$
    – Phil Sweet
    Commented Sep 6, 2022 at 21:38
  • $\begingroup$ I considered increasing the length of the hose but thought if the water rises 12” in the hose that it pushes up 12” of air no matter the length of the hose. The way I understand it now is since a longer hose has more air in it that it will take more water to compress the air to the same pressure. Is this a linear function? IOW will doubling the hose length reduce the pressure by half? $\endgroup$ Commented Sep 9, 2022 at 11:52

1 Answer 1

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Figure out the sensor's output and place a middleman in the circuit. This way you could read in the value and output a fake sensor value to the machine. If it is an analog voltage, you can put analog circuitry in to change the voltage. If digital, you may need to obtain a sufficiently fast microcontroller and program it.

Some of these sensors sense force (hose hanging off a load cell) rather than pressure. If so, you can replace the hose with a stiff vertical pipe of lesser diameter that you can adapt to the existing part, you may be able to reduce the area of water affecting the sensor, 10% less area in pipe that only expands to the hose diameter near the sensor should get you what you need.

For a pressure sensor, you may be able to glue something to the diaphragm to take control of it, or replace/stiffen it.

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  • $\begingroup$ I thought instead of hacking into an expensive circuit board it would be less risky to manipulate the pressure in the hose, if possible. I'll have to try & find a circuit schematic & see what it takes to hack into it . $\endgroup$ Commented Aug 8, 2022 at 6:13

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