Cheap flow detectors

Flowing water is noisy. So a microphone or accelerometer strapped to a pipe will indicate flow.

You could maybe do something with temperature, too.

John

I thought of that. But, *I* can often hear (conducted) these sounds when no one is running water on the property (i.e., neighbors must be!). I've traced the water lines out to the main and figure there is at least 100 feet of pipe between me and the nearest "outlet" on a neighbor's property.

Of course, the source of the sound could be the tap *off* the main for the neighbor's line. But that's still close to 100 feet or more.

I.e., I wonder how reliable that sort of approach would be? I probably would have to do something to deliberately increase the sound associated with water flowing "locally" to reliably differentiate between them (?) -- which increases the noise associated with "normal living". :<

Hmmm... that might work. Though it would have to be seasonally adjusted (e.g., water in the summer is considerably warmer than in the winter; Neither is particularly "cold" as frost line isn't very deep, here)

A friend of mine was going to make a commercial product that basically was a small turbine with a magnet, and a flux sensor to do flow detection and measurement. I don't think he went beyond the prototype stage, though...

As for other measurements, if 'might' be possible to have a resonant field around the pipe, and maybe detect changes in the eddy currents as the water flows. Would possibly work on plastic pipe...

Charlie

Remember the rotating ball in old-style gasoline pumps. How was that done? I don't remember seeing any vanes. Maybe just a slight offset in the pipe is sufficient?? ...Jim Thompson

Measure the pressure drop across a known impedance. You might imagine that someone already makes such a device. I've seen differential manometers that measure the capacitance change as a disk gets pushed to one side or the other.

George H.

On a sunny day (Thu, 15 Apr 2010 12:02:04 -0700) it happened Charlie E. wrote in :

You can probably use Doppler and ultrasound. Just connect a transmitting transducer on one side, and a similar receiver on opposite side of the pipe, and mix the 2 signals, The difference frequency (in low audio howl) should be proportional to the speed of the flow. You can also measure air speed that way.

On Thu, 15 Apr 2010 11:33:11 -0700, D Yuniskis wibbled:

The usual (invasive but ultra cheap) way a cheap flowswitch can work (like in my electric instaneous water heater) is an element with a small magnetic ball inside. This normally sits at the base of the device. The water flow must be arranged to be "upwards". A certain flow threshold will lift the ball as the water flows past. Obviously the ball is captive inside an 1/2 inch long chamber.

Detect ball with reed switch outside (or hall device).

An expensive totally non invasive method is to strap a couple of ultrasonic transducers on and do something funky - I think you can measure flow accurately with this method rather than just detect it.

If the water is expected to be of a significantly different temperature to the ambient air, then a temp sensor could be a goer. Would definately work for hot water (I'm thinking of using it on my central heating to detect stuck actuator valves without spending much money). Cold water detection depends on whether the incoming water from the rising main is reliably colder than any ambient is likely to be. Probably work in England with water typically coming in at 8C or less and ambient being usually much higher in most domestic buildings. Be a non starter in a farm barn or storage facility.

A variation for augmenting this cheap passive method could include putting a small heating element round the pipe section wrapped in insulation. This is going to suffer from conduction leaking heat away down a copper or iron pipe, but 10 watts or so might turn a cheap unreliable method into a cheap reliable method... All guessing of course :)

One typical approach (wastes some power - so it goes) is to run a thermistor such that it self-heats (or a resistor as heater and thermistor to measure - but just one is cheaper) - when the fluid does not move (much) the temperature (or power input if trying to maintain a constant temperature) is considerably higher (lower) than when the fluid is in motion. Thermistors can be cheap. A pulsed strategy might save power, and help with ignoring seasonal variation as well - ie,

?What's the temperature?

?Dump some power in

?What's the temperature now, what's delta T, how does that compare to training runs with flow and without flow?

With adequate training runs and stored data, you can even get some crude flow measurements from that approach.

Leak sensors are probably simpler, though prone to problems of their own.

Lots of people make turbine and paddle type flowmeters.

Most aircraft fuel sensors are turbine meters with variable reluctance or carrier/inductive (zero speed) pickups.

I've done tachs that interface to these. The Cox units are great. They use fuel-lubricated carbide bearings, all stainless parts, very nice designs.

John

I saw a product at one of those Home Depot type demonstration (not sure if it was really Home Depot, but it might have been). It was a cut-off valve. The one they showed was for a toilet. Then then take a hacksaw to the output pipe going to the toilet and cut it in half. Only a few drops of water come out, then the flow stops.

So, if you're sensing just to initiate an alarm so that someone could effect a stoppage of water, be advised that someone has evidently already eliminated this step. The device shuts off the water automatically. No batteries involved.

I don't think devices are well known-- except perhaps to a professional plumber?

Found them: Watts FloodSafe Auto-Shutoff Connectors Link:

-mpm

Ever looked into a magneto-inductive flow meter? I bet some Chinese manufacturer can make the metering bodies real cheap if you order several thousand units.

On Thu, 15 Apr 2010 19:15:29 +0000, Jan Panteltje wibbled:

^^^^ definately

I've certainly seen commercial detectors available (maybe Farnell?) that do this - caveat, not cheap, but the parts probably are if you can DIY

Not just a temperature reading, set an insulating sleeve around a foot of pipe, heat the center, and look at the temp difference at the ends; if there's flow, the downstream end is warmer. AC excitation of a bridge temperature-difference sensor can get you down to millikelvins, and at 3 gal/minute, it takes about a watt of heat to generate measurable differences.

A propellor in the flow, and a window to look at it, is more commonly used.

Thirty something years ago I was given that task for IBM. The problem was leaks between the Cooling Distribution Unit and CPUs of water-cooled mainframes. Since the plumbing was under the floor, leaks weren't obvious. I went to the hardware store, bought a copper toilet ball assembly (only the best for mainframes), grabbed a microswitch, and built the prototype. My boss got the idea (he was one of the good guys) and the project was canned.

That gives a whole new meaning to a 'Data Dump', though. ;-)

A small magnet in a vertical pipe. at low flow speeds it stays down. At high flow speeds it goes up. Then a reed relay, close to the pipe, can be connected to an alarm.

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.

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*!

E.g., you can't use this to tell you if the valves in your irrigation system are operating (for example, by "detecting water" coming out of the valve(s))