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Cheap flow detectors

The training runs / calibration curve will be different than with metallic pipes (and copper will be different than iron, for that matter

- and clean iron or copper will be different than iron or copper with a heavy coating of scale/sludge built up inside.) The thermal time constant will be different. But it should work just fine. Plastic pipes are far from perfect insulators.

The temperature differences don't need to be large. Effectively the approach is trying to measure how good of a heat sink the pipe is, and a pipe with flowing water is a much better heat sink than a pipe with water sitting still - even if it's a plastic pipe.

Easy, but "invasive". Valve, pressure sensor. Quite commonly done in the non-electronic regime (shut off the main valve and look at a gauge while "no water is being used.")

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Reply to
Ecnerwal
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The source temperature shouldn't matter (much) if you use a bridge with two thermistors (one self-heat mode).

Reply to
krw

Sorry, I had viewed a different video than the one you must have linked to.

Yes, I referenced this elsewhere in this thread as: "The devices like that which I have seen are built *into* the flex line. I.e., from the toilet's stop to the bottom of the tank. They aren't general purpose and all seem to be used only in lines with rather low flow rates. E.g., icemaker, toilet and perhaps dishwasher. You might be able to adapt one for use with an RO unit, etc."

But, as I also mentioned: "And, they don't *tell* you anything -- they just shut off the water -- which can be a good thing! :> But, if the property is unattended for a while and, for example, your irrigation system is now effectively disabled, you'll have an expensive homecoming when you discover everything in the yard is *dead*!

I.e., it handles the case where: if (!should_be_flow && flow_sensed) turn_off_flow /* gee, I thought it already *was* off?? */ signal(shut_off_valve_is_not_working)

But, do nothing for the case: if (should_be_flow && !flow_sensed) signal(turn_on_valve_is_not_working)

They aren't very expensive. (the Watts device you mentioned) But, they are part of the flex line. So, they are in a more vulnerable positition than, e.g., a "regular" valve installed in the feed line.

We looked at one of these (72 inch) for the refrigerator and opted just to buy a "non-protected" flex line as the inline valve didn't seem like a long term reliability issue (hard water, etc.)

Reply to
D Yuniskis

Aargh. Another one of those vague questions with no numbers.

RTFM: "

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"

There are, in fact, ultrasonic devices one can clamp to a pipe for flow measurement. What you want is this:

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Clamp it onto a pipe, plug in the Ethernet cable, and read out flow.

You probably can't afford that. You can probably afford one of these:

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but you'll have to cut and thread the pipe to install it.

John Nagle

Reply to
John Nagle

Original question: "to *detect* (not measure!) ... at some threshold"

All of these "solutions" a flow *meters* -- hence more complex than they need to be to satisfy the original criteria.

Reply to
D Yuniskis

Yep. The ball just rotates in the swirling flow. The entry/exit points of the flow in the viewing chamber are offset.

IIRC, these were indicators only to reassure the customer that the pump was in fact pumping something. The older generation pumps had a glass container on top into which you'd pump the gas. Then you put the nozzle into your tank, pulled the trigger and you could watch the gas flow out of the container. Once they eliminated these, there were probably a few customers that didn't trust a pump where they couldn't see something move.

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Paul Hovnanian P.E.

^^^^^^^

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Paul Hovnanian P.E. 

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But...

If the original criterion was that flow would be considered to have
been established at a certain level of flow, then flow would have to
be _measured_ in order to determine whether or not that threshold had
been achieved.
Reply to
John Fields

No, the point is to define some minimum flow rate "of interest". Then, come up with a sensor / scheme that gives you *one* bit: flow exceeds specified threshold amount or flow does NOT exceed. How much it actually is (in bogounits or whatever) is not important.

Reply to
D Yuniskis

Similar effects can be observed "floating" a "ball" in a jet of air. Any flat spots on the ball will "gravitate" (funny choice of word! :> ) to the top!

Reply to
D Yuniskis

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