I’ve never been comfortable powering RO machines with 120v in the SFR water tank.
Additionally, the 100 gal SFR tanks I use are only about 36” high so there’s not enough swing room for the float to open/close the circuit.
And, when the tank is filling the waves/sloshing frequently causes the float switch to open/close several times before it finally shuts off the RO machine. That’s not good for the longevity of the pump and membranes.
My solution is to use 2
Madison Float Switches wired to a 24v DPDT “ice cube” relay. The relay is wired to function as a latching relay. And 120v is nowhere near the tank.
The upper float switch is positioned at the FULL level of the tank. The lower float switch is positioned about 6” below the upper float switch.
When SFR water is consumed the upper float drops and nothing happens. As more water is consumed, the lower float drops and the RO machine turns on. As the tank fills, the lower float rises, and the machine remains running. When the water causes the upper float to rise, the switch closes, and the RO machine shuts off immediately…unaffected by the waves/sloshing.
So, it’s like a machine’s magnetic safety switch…a momentary push button switch to turn the machine on and another momentary push button switch to turn the machine off.
This set-up allows the RO tank to drain about 25-30 gallons before the RO machine turns back on. That means a 2,400 GPD RO machine will run for 25-30 minutes every time the tank needs to refill…again, that’s good for pump/motor/membrane longevity.
For Low Water Cut Off, a third Madison float switch is positioned about 3” above the tank’s outlet. That switch is connected to the Repressurization pump circuit to prevent the pump from running dry.
My installations use the car wash’s high-pressure pumps for SFR delivery to the bays…featuring a high-pressure solenoid valve and 2nd pressure regulator set to 400psi. My LWCO switch opens the 24v neutral to all the 3-way ball valves and the high-pressure by-pass solenoid valves. IF the SFR tank runs dry, the SFR selection in the bays will deliver fresh rinse water at full pressure. The customer won’t get SFR water, and the operator/attendant will realize there’s a problem with the RO system and go look at the empty SFR tank...and I get a service call.