Pressure Switch for Small RO

[bryankloos]

Hey all,

Just curious what is the purpose of a pressure switch an a small (4x150) RO systems for sap?
I see they on the occasional build, but not really sure how they would help with this type of system?
Low pressure turn off? Over-pressure shut-down?
Any help is appreciated.
Thanks,
Bryan

[DRoseum]

Exactly both reasons. Can shut off on low pressure and on over pressure. This can prevent unnecessay pumping (low pressure when there is no sap left) or damage to membranes or system (on high pressure - membranes need to be flushed, etc)

[OGDENS SUGAR BUSH]

Hey all,

Just curious what is the purpose of a pressure switch an a small (4x150) RO systems for sap?
I see they on the occasional build, but not really sure how they would help with this type of system?
Low pressure turn off? Over-pressure shut-down?
Any help is appreciated.
Thanks,
Bryan
low pressure shut off is nice when you want to leave the R/O unattended to do other things and it will shut down when it runs out of sap

[bryankloos]

How does one implement a low pressure cut of for a small hobby RO?
I about to suits up the system and was thinking a cutoff would be perfect for an overnight RO run the evening prior to boiling. The goal would be to turn it on at night and let it run until sap is depleted.
Any advice?

[OGDENS SUGAR BUSH]

How does one implement a low pressure cut of for a small hobby RO?
I about to suits up the system and was thinking a cutoff would be perfect for an overnight RO run the evening prior to boiling. The goal would be to turn it on at night and let it run until sap is depleted.
Any advice?https://www.ebay.com/itm/Hubbell-Industrial-Controls-69WC7-PressureSwitch-3-20-CutOff/223309859315

[UB29]

The RO Bucket guys (see ad above) sell a low pressure cut-off that they sell for about $30.; installed on the concentrate line. Wire in series with your Pump, and it shuts it off when concentrate outlet pressure drops below 5 +/- psi.
Thanks, Bill

[DRoseum]

Exactly. You can buy on Amazon for even cheaper:
Tank Shutoff (TSO) Switch for Aquatec Booster Pumps https://www.amazon.com/dp/B007XVJYZQ/ref=cm_sw_r_cp_apa_i_N2pNDb4ZHDMDW

This is adjustable with a very small allen wrench to increase the top end pressure shut off. I have mine set around 110 psi.

Video here shows where to install: on concentrate line in front of needle valve.
https://youtu.be/s106bSrcfno

[bryankloos]

Do you use a low pressure cutoff to turn off the pump when one runs out of sap?
Is the high pressure cutoff to ensure the pump Donets over pressure in the event of a clog or fault?

I would like to add a switch to turn off my pump when the feed tank runs out of sap.
Which switch would work for this application?

Thanks

[carls47807]

Generally a high pressure condition isn’t a concern. Most booster pumps have an adjustable bypass built into the pump head. In addition, they can’t really get over 150psi anyways (when the bypass is Max’d out).

To set your maximum pressure on an aquatic or similar adjustable booster pump, get it running with a pressure gauge and needle valve. Slowly close the needle valve and set the bypass pressure (usually with an Allen wrench). Once it is set correctly you should be able to close the needle valve entirely and it should hold your target pressure (~120psi).

The low pressure switch is nice to have when running the system over night, or when you aren’t around. Even though the pumps can run dry, there is piece of mind knowing it is going to shut off if a hose blows (instead of dumping 250 gallons of sap) or you run out of sap. The shut offs need to be very sensitive and trip around 15psi. The amazon ones won’t trip until 2 or 3 psi, and it takes forever for the system pressure to bleed down that low (sometimes over an hour).

Carl




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[canaanmaple]

How does one implement a low pressure cut of for a small hobby RO?
I about to suits up the system and was thinking a cutoff would be perfect for an overnight RO run the evening prior to boiling. The goal would be to turn it on at night and let it run until sap is depleted.
Any advice?

here is a video that should show you everything you need to know :)


https://www.youtube.com/watch?v=Q4inzXni44k

[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-1-5-hg-vacuum-switch-with-burner-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.