Low Flow Shutoff for RO

[Ghs57]

Any recommendations for a reliable low flow shutoff. I had my Procon pump burn out when the RO ran dry one time at the end of last season (since rebuilt).

[DRoseum]

I just wired up the GRL8-02 Level controller to start/stop my RO based up sap levels in the tank. All you need are bare wire sensors to measure the level. That relay controller can be configured in different modes.

https://www.geya.net/monitoring-relay/level-control-relay-grl8-01-02/

[Ghs57]

Now that's a cool device, and I may get one for my head tank. I run the RO from several different tanks though, so is there a way to run that against the outflow of the RO? I think that's the kind of shut off I've heard about.

[DRoseum]

There are low pressure switches that will cut out the pump when flow reduces after the pump. You will need to use a momentary switch to bypass the low pressure switch during startup while the pressure builds in your system.

I also pump out of 2 tanks that aren't near each other and set up the overall logic to allow me to bypass this controller if desired and also made my wire sensors with quick connect wire harnesses so I can have a set up for each tank and just swap the connection.

[Bellehollow]

I actually just ordered one of these low pressure switches from Dywer. All SS wetted components and fully field adjustable to pressure. I have not received it yet, should be here in the next few days. As D. Roseum mentions, you will have to have a momentary switch that will bypass the low pressure circuit on start-up.

https://www.dwyer-inst.com/Product/Pressure/SinglePressure/Switches/SeriesA1F

[Bricklayer]

I actually just ordered one of these low pressure switches from Dywer. All SS wetted components and fully field adjustable to pressure. I have not received it yet, should be here in the next few days. As D. Roseum mentions, you will have to have a momentary switch that will bypass the low pressure circuit on start-up.

https://www.dwyer-inst.com/Product/Pressure/SinglePressure/Switches/SeriesA1F

That’s the same style of low pressure cut of switch that I installed in my RO.
Only problem with just having the switch by itself is that the pump will flutter on and off while it’s running out of sap.
I used a relay that latches when the switch goes from NO to NC and a momentary switch to start the pump.
Hold the momentary switch until it gets up to pressure then it stays on.
Once the pressure drops the pump shuts off completely.

[Clinkis]

If you have a feed pump you can use a regular well pump pressure switch with low pressure shut off so when feed pump runs out of sap it will kick everything off. Very simple and doesn’t require much wiring or additional controls. That’s what I used on my last RO and it worked great.

[Ghs57]

Thanks for the responsesThere are a lot of good ideas and solutions here. Does anyone have "how to" instructions/photos on any of these methods? I am a diy guy, and I can figure out solutions most of the time, but help is always appreciated. I'm also in the middle of expanding my shack and installing new equipment in time for the season, so time is at a premium.

[Ghs57]

If you have a feed pump you can use a regular well pump pressure switch with low pressure shut off so when feed pump runs out of sap it will kick everything off. Very simple and doesn’t require much wiring or additional controls. That’s what I used on my last RO and it worked great.

I like this, but at the moment I don't have a feed pump. I wanted to add a post to my RO for this season, but 2020 didn't cooperate. That would have added a feed pump, flow meters, etc.

[maple marc]

How about a float cutoff switch for the feed tank? I can't find a link at the moment but I think something simple like this could be good for people like me with a simple one-pump RO (just got it and am setting it up for the first time). 110 power cord for the RO pump plugs directly into the float cutoff switch. Anybody using one of these they can recommend?

[wmick]

For the pressure switch setup, you should really want a start stop circuit of some sort.... This will prevent it from starting and stopping as the pressure flutters...
Sorry for the crude diagram..
You need a relay or contactor that is rated for the amperage of your motor, and has 2 or 3 NO (normally open) contacts.
One normally open pushbutton and one normally closed pushbutton.

You will need to hold the start button long enough for the pressure switch to close.
The auxillary NO contact from your relay will be closed.... so you can take your finger off the button...

If the pressure switch or the Stop button break the circuit, the coil will de-energize, all the contacts open... and you will need to press start again.

The 2 contacts and "M" on the second rung are your motor... You can get away with just one of those contacts if you need to...
22044

[wmick]

How about a float cutoff switch for the feed tank? I can't find a link at the moment but I think something simple like this could be good for people like me with a simple one-pump RO (just got it and am setting it up for the first time). 110 power cord for the RO pump plugs directly into the float cutoff switch. Anybody using one of these they can recommend?

This would work good... any of the sump pump type would work... Still might need a relay or contactor, if the float switch is not rated to take the motor amps, itself.

[Ghs57]

That's another good idea. But once again my problem would be when I switch tanks. I'm ROing the truck tank into the main holding tank, then concentrating the holding tank (which is also fed by on-site maples), then going to do a wash with the wash tank. A shutoff on the unit solves the problem.