Seros, Steppers or Solenoid Valves

I am building a hydroponics controller and have been beating my head against a wall for over a year trying to research what will be the best form of "liquid interrupt" (valve) to use. There are a few rules that I need to adhere to and they are as follows;

1) The body must be made of plastic or stainless steel - as this is for hydroponics, water will be mixed with salt based nutrients to feed plants. This composition is highly corrosive to all metals and I would much prefer any type of plastic over the stainless steel, especially when considering the price difference.

2) The price needs to be in the $10-$20 range - I am beginning with a 2 site system, and this will require a minimum of 13 valves. However, I do plan to scale up at a later time and will have the need of adding in more valves.

3) The valve needs to allow fluid flow in either direction - About half of the valve in my drawing will need to permit flow in one way or the other.

The red lines in the picture indicate valve placement. The pumps that move the liquids are 400 GPH and are rated at 3.2 PSI. I've been looking at the plastic Adafruit solenoid valves, and many others like it that all require a minimum of 3 PSI, but what I don't quite understand is how several of these valves in series will behave in a 3.2 PSI system? I am also considering possibly using Servos or Steppers to actuate plastic ball valves, but those little valves do take a considerable amount of hand torque to turn them and I fear cheaper motors won't be able to generate enough torque to do the job.

This system will have several routine plotted out in code that include;

1)moving fresh water from the master reservoir (blue circle) and mixing in nutrients with peristaltic pumps to one or the other sites (yellow box).

2)feeding plants 3-4 times daily (grey circle) to (green circle)

3)testing nutrients for EC, PH, and Temperature (grey circle) to testing rail and returned to (yellow box) a minimum of twice daily and corrections made as needed.

4) pumping out spent nutrients to the waste line once every 7-10 days.

The blue arcs fed into the left central rail is nutrients in, and the rail to the right of that is the testing rail that will house Atlas Scientific probes that connect to their respective circuits. they have very nice isolated circuits that work well with Arduino and they will be the backbone of everything once I iron out the plumbing.

Any ideas or feedback is desired. My 3 main requirements are plastic - 2 way flow - & price. TYIA

Thanks for your report - hopefully I've fixed the tags for you.

You might consider using servos to block the flow by squeezing a soft plastic tube. No contact with the liquid. If you organize the mechanics properly there need be no force on the servo's motor when flow is cut off and power to the servo could be disconnected.

...R

Robin2: You might consider using servos to block the flow by squeezing a soft plastic tube. No contact with the liquid. If you organize the mechanics properly there need be no force on the servo's motor when flow is cut off and power to the servo could be disconnected.

...R

Thanks Robin! I never even gave that a thought, and it's not like there'll ever be a lot of pressure in any part of the system.