09 Dec

Constant Pressure Pump

We have a constant pressure pump system serving our dairy. I spent the afternoon pulling the deep well pump and correcting a wire problem.

Background: Pump is a 3hp motor connected to a 1.5 hp pump end on a 2 inch drop hose. Constant pressure controller is basically a variable speed controller. The brand of controller we had was AY McDonald Pressure Master (Subdrive 30).

Two weeks ago, after being in service for 18 months, the controller burned up – literally. In a path along the heat sink, there was massive heat damage. Leads blown off their surface mount pads. Resistors blown apart. Surface mount transistors blown apart. That sort of thing.

Cause – unknown.

$1600 later, I had a new Pentek controller as a replacement. It worked great for 4 days, then gave a Low Amps warning and shut ‘er down. Broke out the multimeter and found significant resistance on the yellow wire at the controller, and then at the well head. Not good.

To troubleshoot further, one must pull the pump. The bottom of the pump sits at 300 feet down the well (the true water formation is from 300 feet to the depth of the well at 320. The last 10 feet are screen.

Well capacity is about 150 gallons per minute. Pump capacity is 35 gpm. Static water level is 55 feet. I could have gone much shallower on the pump set, but I’m always trying to project worse case scenario, and set deep if I can afford it (cost is wire and drop hose), which I could at the time.

So, I pulled the pump today, and lo and behold, the yellow wire seems to have done some rubbing. It had a spot rubbed flat on it’s insulation jacket and the wire as of today was non-existent across that gap. Obviously there was a gradual corrosion occurring. This wire seems to be a 12 gage stranded copper. Not my favorite. The drop wire itself is solid copper 10 gage. The black wire splice also has a spot rubbed flat and was on its way to dying the death.

Wire problem
Wire Problem

Lesson: I shortened the wires at that depth so there is no slack and they won’t rub. I am suspecting they were rubbing against the well casing anytime the pump kicked up some torque and possibly had light movement. Just guessing.

I replaced all the splices and found another area on the wires where there were flat spots and put another set of splices there (this is where I did the actual shortening of the wires). Thanks to our exceedingly short days, I ran out of daylight and will drop this pump back in tomorrow and give it a whirl and see if all is well with the new Pentek controller.

In the meantime, being a dairy, we have a backup – our original 14 foot dug well (this well uses a submersible 3/4 hp pump and runs on an old-fashioned pressure switch). Switching from one to another is as simple as turning off one breaker, turning on another, shutting off one valve and opening another.

Lifting the pump
Lifting the pump