Smarter well pump control

By admin, July 30, 2014

Programmable well-pump control prototype keeps water flowing

A friend was having major problems getting adequate water for a rural rental house. Despite having three wells, flow rates in a geologic boundary zone of shale/sandstone were too low to reliably supply water for four people in the house. He was debating having the wells fracked or another well drilled.

I suggested we implement an “intelligent” control system to pump small amounts of water from each well in turn, 24 hours a day, storing it for use as needed. I acquired all necessary components at very modest cost, wrote a suitable PLC program, and built a quick prototype as my friend installed plumbing. I used an AutomationDirect.com PLC that I have used several times and like for its reasonable cost and state machine programming. [I do think it’s silly they continue to sell the development software for this line of PLCs, which is well past “mature” technology. Why not give away the software as they do with newer PLCs?]

After a bit of tweaking the first few weeks, the system has been working really well. The tenants went from having weekly water outages to having none at all over many months.

A low-cost Koyo text-based display panel (available through AutomationDirect.com) gives statistics on the system and allows changes to programmable parameters:

• time between pump cycles (can be different for each well)
• time of each pump cycle
• time to wait for flow detection

Unlike commercially available systems which implement their pump-control logic in hard-wired timing relays, ours is fully configurable in software and easily expands to support more pumps.

Flow detection makes sure that each well is actually producing and shuts off the submersible pump if:

• the pump doesn’t generate flow within a programmable period
• flow stops before the programmable pumping time ends

Flow detection is done with a very rugged and reliable SquareD differential pressure switch.

If needed, I can interface a system flowmeter to the PLC to add adaptive control to vary pumping parameters based on water usage. So far we have not needed that change, and the system has kept up with water demands quite well.

Water pumped from the multiple wells in stored in recycled food-grade polyethylene “tote” containers. A Grundfos constant-pressure pump maintains water pressure into the house.

Food-grade float switches mounted to the top of one tank control the PLC, and also disable the household pressure pump if water gets too low.