Water Flow meter for 3 inch pipe?


All of the off the shelf parts out there are for much smaller piping and I need a way to measure the flow through a 3 inch PVC pipe. Any ideas on what I could do? I intend to measure the flow rate at the output of the main pump or possibly the input which I theorize would be the same as it is a closed system.

Here is the problem I am looking to solve and why I think a flow meter is the right answer but I am open to alternatives. Without being too specific…I need to measure the Gallons Per Minute actually moving through a complex system of pipes and pumps. Understanding the true rate of flow for a particular system is important as it serves as the basis for a number of calculations that most people are fudging the inputs on.


@LukeUSMC, flowrate measurement through a 3 inch pipe can be done a lot of ways. Take a look here:



I’ve been looking pretty heavily at the ultrasonic transit time approach (which I believe the FLUID guys are using). Simple to attach and no need to cut into existing plumbing. Next sensor to “pick” is a pressure sensor, the transducers out there aren’t BOM friendly at 100.00/each so looking to go indirect there too. I’ve seen sensors that use air but are coupled to the water outlet but don’t know how specifically they are doing that. If I can use a “collar adapter” at the normal gauge mount for a filter then the traditional visual and air bleed remains in place and new capability is near invisible.


Although as you found pressure sensors aren’t cheap either, you could measure DP across an orifice and calculate flow based on that. you could use a microwave, then with some complex calculations you can measure water + air going through the system… but thats not cheap either.

ultrasonic seems to be the norm and easy to retrofit to existing plumbing. i think there was a kickstarter using this approach. not sure if it was open source or not…


Use Bernoulli’s law:

Once you know the speed of the fluid, you can calculate the flowrate using the diameter of the tube,