Pipe flow sensor - non invasive?

[Tim Watts]

Just curious...

There are non invasive sonic based water (fluid) flow sensors that clip onto pipes.

Has anyone ever made or DIYed a simple flow *detector* that can be clipped to an existing 15/22mm pipe? ie does not measure flow (accurately) but detects if there is *some* flow.

Application - leak and tap-left-on monitoring...

Assume mains cold water feed pipe.

I can see a couple of cheap ways of doing it: Some sort of sonic "hiss" detection. Or a thermal detector - eg a heating resistor (metal clad) and a temperature sensor.

Much flow is likely to cool the water assuming the detector is near the rising main and not half way around a hot loft.

[Andy Burns]

Is this to be DIY "for interest"? seems cheap enough to just buy one otherwise ...

[Tim Watts]

Nothing "non invasive" there :(

Invasive is easy - and the cheapest would be to stick a small commodity water meter in - these are very cheap and can be had with a magnetic coupling that can drive a front mounted pickup sensor.

No - I'm looking at a scenario for a mate where the pipe has very little "visibility" before it goes off on all its branches - ie pops up under the sink and then goes everywhere. No room to work to insert anything without destruction of a kitchen unit.

[Andy Burns]

Ah sorry, a quick search for clamp-on liquid flow sensors seems to show plenty ... but they're in the 3 or 4 digit price range ...

[Roger Mills]

Indeed! I'd like a non-invasive clip-on meter - if such a thing existed

- to assist with balancing central heating systems. If you could set the flow rate through each radiator to be proportional to its heat output, you could set a system up very quickly without needing to wait for the temperatures to stabilise.

[Tim Watts]

Yep - those are the doppler effect ones - very "industrial" in their price range...

[Tim Watts]

Getting very DIY now - but I was wondering in your case about 2 temp sensors (Dallas 1-wire jobbies) and a heating resistor at the flow source side.

Without the resistor power up, the sensors should read the same temperature - especially on copper pipe, say 6-12" apart.

Power the resistor up with no flow and the 1st sensor gets hotter with only conduction to move heat to the second sensor.

With water flow, the heat should be removed from the 1st sensor. Or maybe the resistor should be on the 2nd sensor?

This is the sort of thing it would be really fun to do an experiment with - bit of copper pipe on a hose on a tap (hot and cold), couple of temp sensors (multimeter type) and a resistor with a variable PSU.

Simple enough, could probably have a rough and ready stab at a simple physics calc for the system assuming all the heat from the resistor is transferred into the moving water - bit of SHC vs flow calculation should give a rough idea of the possible sensitivity.

[meow2222]

Readings would be very dependant on thermal coupling to the pipe. Casting a blob of silicone packed with al or cu powder could help.

NT

[Harry Bloomfield]

Invasive, but look at car engine MAF sensors - manifold air flow sensors. A +ve, a -ve and an output wire reflecting the flow.

[Richard]

This of any use?

[Tim Watts]

Yes - that does suggest listening to the "hiss" has merit.

With copper plumbing, any noise anywhere will get all around the pipes - but as I am interested *any* flow at the source (mains) so that should not be a problem.

[Tim Watts]

Interesting:

[Dave W]

I would think a slight leak would only involve movement of water in the pipe of less than half a centimetre per second. As the pipe is metal, any cooling would be conducted over a long length of the pipe and so too small to be detected. I don't think there would be any audible hiss either.

See here for descriptions of various ultrasonic flowmeters:

I leave design as an exercise for the reader!

[Scott M]

Since they do invasive ones designed for water, why bother?

[Tim Watts]

I really have to break out my storage box of electronics and start experimenting...