How about these:

https://www.aliexpress.com/i/32695736512.html?spm=2114.12057483.0.0.20da4f38tEQdM3

https://www.aliexpress.com/i/32799629684.html?spm=2114.12057483.0.0.20da4f38fHMazM

Interesting ... maybe I could take one of those apart and see what's inside. Thanks!

 

Another way:

----> https://www.ebay.com/i/263829242251...MI_s-E5bOA5AIViYrICh2_IA8oEAkYDyABEgLUD_D_BwE

Or make yours; A barely sinking 'float' will make it very sensitive. An optointerrupter from outside will confirm/detect its rise from flowing water.

 

I could take one of those apart and see what's inside.

It is stamped on its cover : a paddle wheel

Like :

 

How about just detecting the sound of the water flowing through the pipe !

 

How about just detecting the sound of the water flowing through the pipe !

That's a lot harder than it seems. Imagine all of the other sounds present in a domestic pipe. Besides, what does smooth running water sound like inside a pipe? The only technology similar to what you're proposing is ultrasonic sensing, which is out of the question in this application.

 

In the OLD days , we checked for water flow with just a large screwdriver to the ear ! .

 

In the OLD days , we checked for water flow with just a large screwdriver to the ear ! .

I sincerely hope another worker never hammered on the pipes while you were listening!

 

You sound a very arrogant person

 

Another possibility: hang a thin flexible plastic 'curtain' across the inside of the pipe and attach a tiny magnet to the base of the curtain. The slightest (or largest) flow should deflect curtain plus magnet in the flow direction and the magnet shift could be detected externally with a Hall effect sensor.

 

You want to only detect flow, not measure it?

https://www.amazon.com/StreamLabs-S...flow+detector&qid=1565796211&s=gateway&sr=8-6

 

You sound a very arrogant person

What the? ... NO! ... I was just kidding ... I sincerely appreciate your trying to help me here.

EDIT: besides, didn't you notice I hit the like button on your comment?

 

Another possibility: hang a thin flexible plastic 'curtain' across the inside of the pipe and attach a tiny magnet to the base of the curtain. The slightest (or largest) flow should deflect curtain plus magnet in the flow direction and the magnet shift could be detected externally with a Hall effect sensor.

That's a possiblity... but maybe it would be affected by the pipe's position (vertical or horizontal), which I'd like to be anything the installer chooses.

 

You want to only detect flow, not measure it?

https://www.amazon.com/StreamLabs-S...flow+detector&qid=1565796211&s=gateway&sr=8-6

$200 usd is a little over the top for what I want. But thanks for the suggestion.

 

If the pipe interior is at domestic mains pressure then a small pressure drop should be tolerable. You could have an interior flap valve normally held closed by light spring force. Opening a tap to demand flow would create a differential pressure enough for the flap to move against the spring force, opening the valve. Mount the magnet on the flap.

 

Your paying for WiFi on that one. Doesn't really give any info on the detect method. The cheap flow measurement method is the venturi tube. Then there are differential pressure across an orifice plate, Coriolis effect, and even nuclear gamma-ray devices. Coriolis and nuclear are bot "Non-Intrusive" devices and measure from outside the pipe. Somewhere there should be a flapper valve type indicator device that when the fluid in the pipe flows the flap swings opens and pushes out an external indicator and also serves as a check valve but I'm not finding one.

 

If the pipe interior is at domestic mains pressure then a small pressure drop should be tolerable. You could have an interior flap valve normally held closed by light spring force. Opening a tap to demand flow would create a differential pressure enough for the flap to move against the spring force, opening the valve. Mount the magnet on the flap.

That sounds very interesting ... but how do I guarantee that the flap would wiggle on throughout both flow extremes? Its wiggling frequency is not important, only that it does.

 

There's no wiggling with the post #34 suggestion. Why must it wiggle? Hall sensors can respond to static and moving magnetic fields. Can you give the reasons for your constraints?

 

There's no wiggling with the post #34 suggestion. Why must it wiggle? Hall sensors can respond to static and moving magnetic fields. Can you give the reasons for your constraints?

I've noticed that some hall sensors stop detecting when they're exposed to magnetic fields continuously for too long... that's why I'd like it to wiggle, but I'm going to make sure and test it.

And on the plus side, wiggling frequency could give me some very rough estimate on flow. Although I know I've already said that flow measurement is not really necessary... just trying to leave an open door here.

 

You sound a very arrogant person

He is not. He is a regular contributor with an excellent reputation. Note: 6K messages, over 7K likes.

The majority of the responses so far, including yours, have ignored a critical requirement in post #1:

A reasonable lower limit for flow detection would be 0.1 lt/min. That would yield a flow linear speed of approximately 1 mm/sec.

That is one inch every 25 seconds, or one foot every 5 minutes; a *very* slow linear velocity. I don't think any amount of digital signal processing could extract enough of a change in acoustic spectrum to make a *reliable* determination.

More details are in post #5:

I need to either rotate or shake a small magnet so a hall effect sensor will pick its presence. That's a design constraint and it can't be changed.

ak

 

Hack into this:

https://www.amazon.com/Orbit-Water-Flow-Meter/dp/B00XKQWNTC