How does the flow sensor work for Gen2?

I am new to flow sensors, and have ordered my upgrade to the Gen2 - anything to give the rachio more information about the water that is actually used is worth it to me. How does the flow sensor work - and where would it need to be placed to measure the flow? Right at the ingress into the house? How would it differentiate the flow created from the Rachio and other flows? And if it’s not at the ingress - I have valves all over the place, with multiple tie-in’s - so that wouldn’t work either.

Thanks for the information!


It must sit between the meter and you valves. The software is not out yet so that’s all we know for now

Most sprinkler installations have a single tap into the water line near the water main and branch out from there, typically with a master shutoff (manual) valve and a back flow preventer. The flow sensor would have to go at that location.

If your system is distributed (taps into multiple hose bibs for example), there would be no place to put a flow sensor.

Ok - in a master planned sort of situation that would have worked - my house is an older one and I basically have 3 sets of valves on different sides of the house. I guess no flow sensor for me!

I’m guessing this will be most useful in new systems. Not quite sure yet how to make it work in mine. I do have a single connection into the water main, but will have to do a good bit of trenching to wire it up.

@mathewbeall, great question. We’ll be adding more documentation once we can process the flow meter data, but in short, installing a flow sensor is a 4 step process:

  1. Mount: Follow the instructions provided in the flow sensor’s manual to install the flow sensor at the desired location. (Example from CST) Each flow sensor comes with its own instructions for where the sensor should be installed and aligned. Usually, a formula for the placement of the sensor is used based upon the size of the pipe. An example mount/installation is below:
  2. Wire: The flow sensor wires should be shielded as to reduce the risk of electrical interference. Avoid running the flow sensor wires in the same wire harness as the valve wires (increases the likelihood of signal noise).
  3. Connect: There will be two wire leads that extend from the flow sensor. Insert each wire into the Gen 2’s sensor terminals.
  4. Setup: Within the app (see this support article for details)…additional steps may be added in the future.

I’m looking at a Flow sensor for my farm’s pressurized pond water system… I was planning on using a Hunter… please see attached.

By the way, love our Rachio. Just ordered Generation 2. It has saved us More than 1,000 dollars in the 6 months we’ve had it. I saved you a copy of my water bill if you’d ever like to use it for promotional purposes!



Here is the actual sensor…

@carlos.portu, awesome! You shouldn’t have a problem with the HFS Flow-Sync, but you’ll need a FCT Tee to insert the HFS into. Please see Hunter’s spec sheet for details. We added FCT Tee’s up to 2 inches into the app’s defaults, but we could go up to 4 inches if needed. Just curious, have you already purchased a flow sensor?

That’s amazing! We’d love to review your water bill(s) if you’re willing to share them with us :slight_smile: We’re thrilled to hear we’ve been able to save you both money & water!

Best, Emil

@emil has the spec been clarified for the flow sensor input? I was going to purchase one that can run on up to 24vdc with a Hall effect sensor with a pulse every gallon or every 1/10 gallon (selectable).

Here is our current list of flow sensors we plan to support. Let us know if you have any questions after checking these out. Thanks!


I was looking at an official water meter with a dial…

Hi brkaus,

Our flow sensor input is only designed to work with irrigation flow sensors. The irrigation flow sensors that Franz listed above are specially designed to work properly with the voltages and signals readily available to most irrigation controllers, like ours. I hope this helps.

  • Brad

That’s fine. What are the voltages? They The hunter flow specs say 24vac, but not sure it’s right. Assuming I can match that, it should be easy to add a genetic. 1 gal per pulse no offset??

Given the 24vac input, I’m assuming it’s below 24v. Is it DC or AC?

Hi brkaus,

Irrigation flow sensor requirements sound quite different from what you’re looking at. Our supply outputs 34V DC. This is a convenient DC voltage for irrigation controllers because its simply what you get when you rectify 24VAC. There is another twist, in that the 34V supply line is also used for the data transmission. This means our 34V DC line is relatively high impedance and incapable of supplying much power. Irrigation flow sensors are designed to be very low power. The only connection to these flow sensors is + (for power and signal) and - (for return path). All of the irrigation meters also put out a pulse that requires a K and offset value to convert to velocity/volumetric flow. There’s more information about this in the CST FAQ below:

At this point, I don’t believe there’s software support for a different pulse encoding.

I guess I’d like to understand why you want to use a flow meter other than the supported irrigation flow sensors? If this is a common use case, we may be able to support it in the future.

  • Brad

I guess for roughly the same price, I’m not sure why I wouldn’t use a standard water meter? I like the fact that it has a manual dial for double checking. I also have a 1" irrigation pipe and my zones vary from 1.5gpm (dripper) to ~26gpm. None of the flow meters show that wide of a range skimming through the specs.

I do realize that a meter may have more pressure drop, but my street pressure is 110psi+ and I go into a pressure regulator down to 60psi for the irrigation system. Probably I’m lucky in that regard.

Reading the spec (thank you), a K factor could easily be created (1 if I understand correctly) with a 0 offset. So software wise, that should be easy if I ask nicely :smile:

That leaves the electrical concern. One option with the meter I was looking at was a 24vdc hall effect sensor. Other was a 24vdc/vac reed switch. I think all the other sensors have a hall effect sensor. But should be very low power like standard irrigation sensors.

Thanks for the reminder on the rectified 24vac… Should have remembered from my EE days… but now I’m a 1/0 person.

Anyway… I guess my reason for a regular meter is “why not”… I was considering this meter - FTB8010B-PR

Hi brkaus,

It looks like the CST 1" flow sensor goes from 0.86 GPM to 52 GPM, so you would be ok with that one (called out on pg 2 of CST’s FAQ). I can see where you’re coming from with the dial… I don’t know any irrigation flow sensors with a dial.

I’m digging deep here on flow meters, but here’s my understanding. What you’re looking at is a volumetric flow meter that pulses every gallon (or tenth of a gallon) of water, where the typical irrigation meters measure velocity. I guess you could say what’s the difference because you can convert velocity to volume by multiplying by a constant;) I think where it’s different is this: The velocity sensors that we typically use are sending many pulses per second while a volumetric (say the 1 pulse per 1/10th gallon) meter running at 1 GPM is only pulsing once every 6 seconds. The way our software works (Franz, correct me if I’m wrong here) is we take a sample of the pulses to measure frequency over a short span of time, say a second. With a volumetric meter we may not see any pulses or we may see one. The math should work with a K of 6 and offset of 0, but I don’t think our software would support this off the shelf even with the correct K and offset… Sorry to be a downer here, but I would hate to send you down a path that I don’t think would work with our controller.

  • Brad
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Much appreciated discussion. That’s why I’m asking! I was looking at the other brands, yes, the CST does have a wider measurement range. That’s good to know.

The FSI-T10 shows a output frequency range 0.3 Hz to 200 Hz, so I assume the 0.3hz would be at .86gpm. So yes, that range would be quite a bit different than a meter even if at 1/10 gallon. But the K of a 4" CST flow meter does go to 4.5, so not that far out of range.

Most home automation systems I have looked at do simple pulse counts rather than frequency measurements. I have a power monitor that has a 1-wire bus that can also do pulse counting. That’s actually how I ended up down the path of the particular meter I was considering. I was about to put one of these in before the future rachio flow feature was announced. It is also why I presumed the rachio would be doing pulse counts.

I do still like the dial idea. And the CST meter actually costs about the same as the volumetric meter. I’m betting the reed switch rated at 24vdc would work fine under such low current. Of course reed switches do wear out…

Going to have to sleep on this one…

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@brkaus sorry, I’m coming in late to this discussion. Please keep us posted on what you decide to do. Flow sensor make/model aside, what are the top 3 things you hope to accomplish with a flow sensor? i.e. reports, shut down the system if an overflow is detected, etc.

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The fact that you can pick up used/surplus water meters with a pulse output for around $30 is a great reason to add support for volumetric. Plus it’s easier to implement in software.