Damned Projects! (2025 Update)

Those push-fit hoses are the worst by miles. I had one just let go out of the blue for no apparent reason (the usual failure mode!) This was on the high pressure water intake to the washing machine. Fortunately I was at home at the time in the bathroom next to the utility. I just heard this rushing sound which I quickly realised was escaping water. I was able to shut the supply off pretty much right away, but even so the floor was soaked with water seeping out into the passageway. After that little warning, I replaced all the push-fits in the house with conventional soldered copper pipe connections. Plumbers tell me the damn things are known for this kind of thing and become flaky after about 10 years.

I kind of suspected that was how they worked; nice to have it confirmed.

That will be very interesting when the washing machine enters a spin dry cycle with a moderately unbalanced load and starts shaking violently.

Replacing the hoses periodically is probably a much safer option YMMV.

Japanese washing machines are typically installed with a drip tray on mains drainage plumbed in underneath to accommodate any systematic failures. I have never seen than done anywhere else.

Mine's spinning now, but not unbalanced. Doesn't yours automatically shut off if it shakes too hard?

Yes, they need to be replaced as they were install back in the 1980s.

No bulges, no stainless steel braid, real hoses, probably not made in China, perhaps USA?

I think that's a good idea but usually takes more of a house floorplan change than is all that easy. In a large house it would make senss to have a utility room with the washer and hot water header on a concrete floor with a floor drain...

LOL! Perhaps I should clarify. The hoses between the fixed plumbing and the machine itself are still rubber ones. But they're NOT push-fits. They screw-in.

I would not sleep soundly with *any* push-fits anywhere in the house. That's why I had them all swapped-out for old-style copper. An ex-girlfriend of mine used to manage a care home for the old and feeble. One day, a push-fit failed and spewed water out which ended up cascading down the stairs like a tropical waterfall. All the staff on duty at the time were female, didn't know where the main stopcock was located and had *no* idea what to do other than call an emergency plumber. By the time that leak was remedied, tens of thousands of pounds of damage had been caused. Push-fit? NO THANKS.

Do the five Schmidt triggers in parallel after the oscillator act as a buffer? This guy follows your example:

All things considered, Wanderer's refractive sensor looks like the best bet so far.

And now some comic relief for the artistic, mad man mentality; a Fritzed

Danke,

Here's the physics of a rain sensor:

When you rotate this sensor on its side it ought to work:

If it's high enough, you probably can fabricate (print) it as a single piece and leave the cover off altogether.

Danke,

Here's the physics of a rain sensor:

When you rotate this sensor on its side it ought to work:

If it's high enough, you probably can fabricate (print) it as a single piece and leave the cover off altogether.

On the other hand, a cover does keep the dust out. Accumulated dust appears to be the bane of a refractive water sensor.

Danke,

In this pareticular application, the source impedance of the signal is effectively in series with the resistance of the conductivity cell, so it needs to be as low as possible or it will affect the linearity of the highest conductivity range. This resistance is made 0.5 ohms by the bottom resistor of the voltage divider which drives the cell. (Two

That means that the top resistor of the divider needs to be in the region of 750 ohms to get a reasonable signal. Such a low impedance across the output of a CD40106 could cause current limiting which would give unpredicatable output levels, so several sections in parallel ensure that there is no overloading. All the sections must be driven identically and be in the same chip, so that there is no significant time difference to give rise to a moment when one output switches before another and a huge current spike is drawn from the supply.

Besides, what ekse could you do with all those unused gates?

I would also recommend that the female staff all be taught how to turn the water off. It isn't all that hard.

Joe Gwinn

Use graphite. Two pencil leads.

...

An optic fibre glass will do as well. Shaped in a curve, without the cover. When wet, the light gets out of the fibre. You may have to search for the right fibre, but I have seen this used commercially.

You can probably adapt this technique to the task:

Make your own non-inductive graphite resistors

Is electrolysis mitigation the sole benefit of using AC instead of DC? Is there any other reason to prefer AC?

Danke,

Operating at say a kilohertz or so gets one well above the flicker noise down around zero hertz., greatly improving SNR.

Joe Gwinn

There are two effects caused by electrolysis: it attacks the electrodes and it builds up a non-conductive film of gasses. Even if the electrodes are made of something non-corrodable like carbon or platinum, the sensor will rapidly go high imnpedance because of the gas film.. For both short and long-term stability, it is better to use AC.

Another problem is detecting the change caused by an increase in conductivity. A pair of electrodes will develop an electrode potential of possible more than 1V, the sensing system for DC needs a signal significantly greater than this for reliable operation. High voltages will overcome the gassifying effect but may lead to the formation of reaction products between the electrodes and the electrolyte, which may turn out to be poisonous.

The last thing you want to discover if your kitchen floods is that the sensor has rendered tha puddle electrically live and toxic.

graphite is still eroded.

Not very quickly though so for a sensor where being wet is an immediate fault condition I doubt if it really matters. You could always use gold plated contacts or if money was no object pure platinum electrodes.

Both of those noble metals are almost impervious to corrosion.

Almost? You can bury a gold coin in whatever ground you like and if you lived long enough to dig it up again 1,000 years later, it would be just as you left it. That is a truly remarkable property of noble metals (especially since they're also a store of value and aren't eroded by inflation any more than they are by oxidation/corrosion. In Roman times, an ounce of gold would buy you a decent hand-made suit of the style of the time. Today an ounce of gold will *still* be worth enough to buy a hand- made suit. Remarkable.