Objective: Improve the original design by adding a solenoid to the main pipe. The solenoid should stop gravity and siphoning from draining all pipes after the pump shuts off.

General concept:

  1. Modify the tank to include an inline solenoid
  2. The solenoid is normally closed. When the pump is energized the solenoid is also energized open, meaning they can have the same power source/control if it can handle the load

This change worked well.

The pump switches off and the solenoid closes at effectively the same instant, preventing the siphoning effect seen in V1.

Parts:

  1. Vivosun 800PGB Submersible Pump (3000L/H, 24W) ~ $25
  2. Tank (trash can, cost more than the pump!)
  3. 1/2” NPT Brass Electric Solenoid) (12V DC) $33 - seriously over-engineered for the job
  4. Hoses, adapters and drip sprinklers
  5. AC Switch (I repurposed a Phillips Hue switch)
  6. AC to 12V power supply for the solenoid

Tank with submersible pump and solenoid

I selected this solenoid because it was the right diameter (1/2 inch), normally closed, and 12V. It can handle MUCH more pressure than necessary but I figured I could use it in other projects when this is dismantled.

I included a back pressure valve inline with the solenoid. I don’t think this pump is susceptible to damage, but as the solenoid slams shut I was wondering what kind of reflected wave that would create. The valve in theory contains it.

I used rigid tubes within the tank because the solenoid is so heavy. The water pressure is still very low.

The tap shown at the outside of the tank was in case I need to reduce the amount of water flow. This connects to the same flexible pipe as in V1.

Lessons learned:

Pipes: Most of the standard garden irrigation equipment is 3/4 inch. I chose a pump with a 1/2 inch outlet which made it harder to find parts at that diameter. The 3/4 garden solenoids were not cheaper than I could find.
Condensation: I keep the lid on the tank to minimize evaporation and avoid leaves, but condensation forms on the underside of the lid. This drops water on the solenoid which is not waterproof. It hasn’t been a problem yet, but it looks like the solenoid will eventually fail from moisture. It needs a cover.

Other limitations:

  • This pump won’t automatically switch off if there’s no water. When the water is low it keeps running. Now that there isn’t an anti-siphoning hole it can run dry. I don’t think this pump will overheat, but there is no longer any work-around and I don’t have water level monitoring yet.
  • (Continued from previous version) As it’s only using a basic switch and no monitoring, if the switch fails to receive the signal to turn off (which happens with home control systems that depend on the internet and wi-fi) it’ll over-water the plants until the tank is empty. It can’t detect it’s been running for too long.