water flow detection in a pipe

I have a pipe diameter(lets say 6 inch size). Water pressure flow rate 0 to 20 GPM. Pressure max. of 31 bar.

Always there will be water available in the pipe. When there is flow of minimum 4 gpm, I want to get a signal that the flow is present. (signal could be relay actuating or any other form)

I knew that there are commercially available products like paddle type flow switch.

Want a very cheap and innovative solution for this.

Please share your thoughts.

Hi,

Want a very cheap and innovative solution for this.

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Yes, for sure. Everybody wants this.

Then it's time to invent it. Do you have an idea?

Let's say I have an idea, then I need a partner for marketing and selling, because I'm a developer only. Several thousands.
Or are you interested in a one piece solution? ... or a ready to buy solution?

Klaus

I agree with Klaus, at least tell us if this is a 'one off' to build at home or a mass produced item, it makes a big difference to the solution.

In general, you could consider acoustic devices, make a noise at one point of the pipe and listen for it 'downstream'. Sound waves will travel more in the direction of flow than against it and the levels will depend on flow rate and presence of water. I have no idea how to convert the results back to gpm or any other unit, you would have to work that out for yourself as each situation would give different results.

Brian.

Hi,

good idea, Brian.

Speed of sound in water is about 1500m/s.
if there is water flow, then in one direction the speed of water flow adds to the speed of sound, in the other direction the speed of water flow subtracts from the speed of sound.
Now if you place two sensors in equal distance from the source of sound ( One sensor up the pipe, one sensor down the pipe).. you get two (delay) timing signals.

I recommend to use 2 sensors, because it automatically cancels drift by temperature, drift by pressure, drift by purity of water..

I did some calculations: If my math is correct then in a 6" pipe a water flow rate of 4Gpm is just a water speed of 0.016m/s. (I really hope this is not correct).
This is not much compared to the 1500m/s of speed of sound. only 1/100,000. Hard to detect...

Klaus

Try a microphone in contact with the pipe. When flow rate becomes fast enough water makes a noise in pipes, say 1/2 to 1 inch diameter. It's most easily heard in a quiet house, a sort of pink noise coming from nowhere in particular. Of course acoustic detection works best in a quiet environment.

You might try temperature sensing to detect when hot water starts flowing in a cold pipe. To measure flow rate, notice the speed of temp change as the hot water first arrives. Quick increase in temp suggests faster flow rate.

I have a pipe diameter(lets say 6 inch size). Water pressure flow rate 0 to 20 GPM. Pressure max. of 31 bar.

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It helps if you follow all the units in the same system; 6 in dia pipe; o pressure diff corresponds to zero flow but max pressure diff 32 bars corresponds to a flow of 20 GPM. These numbers do not appear to be consistent.

Please spell out the requirements in detail.

Consider flow and pressure as independent parameters. Pressure is important for "invasive" sensors.

0,015 m/s seems correct and is quite low. An arbitrarily selected 6" industry standard paddle flow switch has a threshold of 50 to 70 GPM. (See kobold.com)

There are several measurement methods that work in the low flow range, but they aren't simple or cheap. The OP didn't explain why he wants to design in this low range.