Irrigation Chemical Injector Pump

[pipeman]

My irrigation well has probably the highest iron concentration ever seen. About 18 months ago, my latest effort to solve was a "Rust Service Company".

They installed a chemical tank and a small injection pump, wired in parallel to the well pump. Whenever the pressure drops, the pressure switch closes, turning both pumps on, adding a small concentration of chemical.

This chemical is supposed to (I think), entrap the iron molecule, preventing oxygen in the air from combining and forming "rust". Works okay for all the large spray heads, but that larger molecule seems to clog my rotors (over time.

I also have five drip zones with 500 or so drip emitters, all of which are now clogged tight. I am replacing now, but this is a job! Also I have several hundred feet of drip pipe with built-in emitters.

I need a better fix. I am trying to come up with a way to disconnect the injector pump whenever a drip zone is turned on. The iron, although it discolors the emitter and a small area nearby, never discolors sidewalks, walls, etc.

My controller is a Hunter and I have considered some sort of relay cut-out, but acquiring that signal has me stumped. I need a 5-way "OR" gate that accepts and passes 24v AC.

 

[JimS]

Take a diode from each zone that you want to disable the pump into a capacitor. This will give you DC voltage for any of those zones. Feed this into a DC coil relay. You may want to use a regulator although something like the common 7805 has a slightly lower than needed max input voltage rating. Then hook the NC contacts in series with power to the injector pump (or use it to switch 24VAC to another relay).

Or you could do the reverse - use diodes from all zones you want to use with the injector running and wire the injector pump to the NO contacts. This would avoid the pump getting a small pulse of current when the zones without the injector first turn on but that may not be an issue.

I did something similar to combine the master valve signals from two control panels. I can take a look at my notes later and give you more detail if you want.

 

[pipeman]

You're thinking of a diode, cap, regulator and relay for each zone?

I should also say that I have been thinking about a sprinkler override system from my ELK in the future.
My thinking is to let the Hunter controller do all the day to day work. The Elk could step in and cancel any or all zones for weather (and maintenance)reasons. The Elk could also send commands direct to each valve to add watering for new plantings etc.

 

[JimS]

You're thinking of a diode, cap, regulator and relay for each zone?

No. Just a diode to each zone. Cap and other stuff is common - just one. When I thought about this a bit more I remembered that I didn't use a regulator. I just fed the cap voltage into a solid state relay and switched 24 VAC with the output. No need for a regulator that way.

I think using the Elk to turn on and disable individual zones in cordination with the Hunter controller is going to be messy - difficult to get it all working together smoothly. Will be interesting to hear about it if you put something together though...

 

[pipeman]

This is what I plan on doing...I think.

I already wired the diodes, capacitor and relay. It works, but I used a 1000 microfarad cap and I think the current drain on the Hunter transformer was too high. It was much hotter to the touch. I wil be going to the far end of the cap design today, with a 10 microfarad in series with a 220 ohm resistor.

Comments on the Elk integration?

 

[JimS]

On the heating... What is the coil voltage for the injector relay? With the diodes it will get about 35VDC. Average voltage will be less with smaller capacitor and RMS current in the transformer will go down and help the heating. If it is a 24VDC relay you may need some sort of dropping resistor as you suggest. It should be a DC coil relay. The resistance can be adjusted to give the proper voltage. If the hunter transformer is still overloaded you could drive a smaller relay or transistor that switches the larger relay and use another transformer to drive the big relay.

Looks like you have a pretty good arrangement so the ELK can take over or disable when desired but otherwise the Hunter does the job.