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post #1 of 8 Old 01-12-2019, 06:42 PM - Thread Starter
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Calling all engineers, water flow switch

Not an area I have any experience with. I'm curious about sensing water flow for the purpose of sending an output signal to an automation controller. Nothing as fancy as a flow sensor to measure actual flow rate, though I guess that could be a fallback. More of a simple yes or no flow state output when a threshold is reached.

Specific application would be on a tub filler, so no need to detect tiny leakage flows. Something like 1L/min threshold perhaps.

From reading/Googling, it sounds like maybe I'm looking for a flow switch instead of a flow sensor. But there seem to be dozens of different variations. Any tips to narrow my search? Guessing output of 5v would be useful, could be as easy as a reed switch connecting external power supply.
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post #2 of 8 Old 01-13-2019, 03:00 PM
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whats the "threshold" that is reached?
a container is filled and that's the threshold? Maybe you really are looking for a level switch and not flow? If level, RVs have sensor systems to determine level.
a boat bilge pump has a level switch.
a condensate A/C tank has a level switch.

Describe your use case to narrow in, not on the device you are looking to find.
EDIT...oh, you are trying to fill a tub...is the tub fiberglass or metal or ceramic / tile?
there are ultrasonic level sensors that would mount to the bottom of the tub that will tell you how much liquid height is above the sensor.
You would need a real control system to have the rule of has it hit your "threshold" or not and then to turn the water flow off.

Are you looking to regulate the temp as well? Or will you manually set the temp balance and put a single solenoid on the blended output (that is simple).

Less precise would be to put the fill valve on a timer and just keep it open long enough to get your tube approx. filled. BUT....if the system fails and there is no overflow protection...this could be a very expensive solution.

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post #3 of 8 Old 01-13-2019, 04:10 PM - Thread Starter
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Not looking for level, just flow. Short version, determine whether water flow for tub filler faucet was on or off. Don't need to know the exact flowrate. Only need to worry about the 99% everyday scenario where there will be modest flow rate. Guessing a threshold of 1L/min would suffice, meaning whenn flow was at that rate or above output is positive or switch closed etc.

Specific use... send signal to automation controller to turn on lights over tub when water turned on. Keep them on until occupancy sensor says no more motion in bathroom.

Just a thought exercise at this point in thinking through ways I might want to leverage a lighting system and automation controller. Trying to figure out what is possible, impossible, or just impractical, and what planning needs to happen to make something work.

For example, in this case the tub filler hardware will mount on a wall that is shared with shower on the other side. Even if I were to find a suitable switch and getting suitable signal to a controller isnt difficult, the switch needs to be serviceable. Meaning not enclosed in the shared tiled wall. Would have to find some upstream access point that could allow for service from an adjacent closet, attic etc, and talk to the plumber about whether that was possible or even allowable by code.
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post #4 of 8 Old 01-14-2019, 11:58 AM
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You can use a "Zigbee" or "Z-Wave" moisture sensor with the sensor probes in the water stream. Once water is flowing, there will be conduction between the probes. That will then signal your automation controller to do "stuff". Once the flow stops, no more conductivity and the automation controller can have a seperate defined event for that.

The sensors are battery and last about 3 years. So, easy installation. We can assist end to end if needed. Send me a message.

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post #5 of 8 Old 01-14-2019, 01:27 PM - Thread Starter
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I would think the pressurized plumbing lines (pex I'm assuming in my case) would stay filled with water indefinitely, and thus keep sending a signal? Thinking I need to detect flow of water, not presence of water.
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post #6 of 8 Old 01-14-2019, 01:30 PM - Thread Starter
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BTW, for clarification I'm talking about something involving the supply line, probably hot side since that will always be used first, some distance upstream from the actual faucet/filler hardware.
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post #7 of 8 Old 01-14-2019, 10:42 PM
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I would put the sensor right on the faucet outflow. That has no water when the valve is shut off.
Certainly if you are going to be on the pressure side, then you will need a flow switch plumbed in. With a contact switch or an "impeller" that measures flow rate. Flow rate will typically be more difficult to integrate as you will likely have to have a custom software driver to understand the data the sensor outputs. And a rule in the controller that is set at "more than zero flow".
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post #8 of 8 Old 01-15-2019, 08:29 AM - Thread Starter
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Yeah, I don't want anything visible if I do this. Would only consider upstream monitoring. Again, not an area I had any working experience with as an engineer, but there seem to be a class of flow switch devices that are binary on/off at preset minimum flow rate threshold and that seems much easier to deal with than pulses from a flow sensor. Just have to do more research I guess to see which specifically might be a suitable choice.
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