# Building an inline water meter for a kitchen faucet

#### HazenAL

Joined Sep 1, 2020
13
Hello everyone,
I'm trying to design a water meter for a kitchen tap as a university project. On the top of the faucet, I plan on having a dial (like a watch face) to indicate the amount of water used- up to 120 liters.
The constraints I have set for myself are that whatever mechanism is used to measure will have to be powered by the flow of water- thus, some sort of propeller/impeller. And the device will be compact enough to sit flush with the top surface of the tap.

The diameter of the inner pipe in which water flows will be 15mm, and will have a flowrate of 7L/min. I have done the calculations and have found that with a 90% efficiency turbine I can generate 0.023W of power. Therefore, after 120 liters are discharged and 1 revolution is made on the dial, a total of 23.79W is generated. For the dial to indicate 1 liter has been used, it has to rotate 3 degrees using a max of 0.195W (23.79/120).

This device can be broken down into 2 parts: 1 that sits inline with the water flow and propeller and 2 is the dial turning mechanism. Im converting mechanical energy to electrical back to mechanical.

If I use 2 motors in each, one to generate a voltage, and one to turn the dial, that will be over engineered and inefficient- or so I think.
I'm trying to find stepper motors used in watches, but I cant find any online.

#### WBahn

Joined Mar 31, 2012
26,304
You are confusing power and energy.

You will only have 7L/min when the faucet is wide open (or at least that's what I'm assuming that flow rate is for -- if it's the rating of the service then it will likely be considerably less). So what if someone opens up the faucet just a little so that only 0.7 l/min is flowing?

#### HazenAL

Joined Sep 1, 2020
13
You are confusing power and energy.

You will only have 7L/min when the faucet is wide open (or at least that's what I'm assuming that flow rate is for -- if it's the rating of the service then it will likely be considerably less). So what if someone opens up the faucet just a little so that only 0.7 l/min is flowing?
Thank you. The 7L/min is for the max flow. If the tap is open at a smaller flow rate, then the RPM will be a lot lower, and less charge is generated.

#### Sensacell

Joined Jun 19, 2012
2,632
The energy of the moving water is very small, so small that you will have nothing left after you try to convert back and forth between electrical and mechanical forms.
Stick with direct mechanical- just like all the existing in-line flow meters that are used to meter water consumption.

A positive-displacement type of impeller will work much better- avoid the low-flow dead zone you with otherwise suffer.

#### Alec_t

Joined Sep 17, 2013
11,748
The diameter of the inner pipe in which water flows will be 15mm
If you're actually going to build this project, rather than just design it, it would be simplest to stick to standard pipe sizes. In the UK (at least) a nominal '15mm pipe' has an outer diameter of 15mm.