Pressure Switch for Small RO

[Msboucha]

Pressure switch works okay, but I've found its not perfect because many times if you spring a leak, the pressure doesn't actually drop enough to shut the system down. If it's a shut off when your tank is empty that you are after, a bilge pump float mounted in the bottom of the feed tank works better - it takes a long time for the pressure in the membranes to drop so the pump is running dry for a while until the low pressure switch triggers - a float shuts off immediately. I have two switches wired in series on mine - Low pressure or empty tank will shut the system down. Build in a bypass switch so you can override the system when you start up and the pressure is under the low pressure switch or when you want to empty the lines when the tank is empty.

[TonyL]

I also had problems with residual pressure on the membranes being too high to allow the low pressure switch to open. I thought about going the float switch route, but wanted to drain the sap tank as low as possible, and a float just wouldn't allow a complete drain down. this season I'm going a different route...I've installed a normally open vacuum switch on the intake side of the RO pump. Upon testing, it looks like exactly what I needed. It closes at 1.5" of vacuum, and will open as soon as the intake pipe in the sap tank gets a gulp of air. It leaves less than a half gallon of liquid in the tank. I do have a bypass switch in the circuit, which I hold closed until vacuum closes the switch. Paid less than $20 dollars for it If I recall.

[bryankloos]

Can you post a link to the vacuum switch you used?

[TonyL]

I used this:
https://www.powerwash.com/mtm-hydro-...r-control.html

I made sure to mount it higher than the level of sap in the tank, so sap will never contact the membrane in the switch.