After looking at pictures and checking the pump curves, this is what I think. It would be very helpful to know the pumping level of each well. With such high static water levels and such good recovery rates for each well, I doubt that the water level is drawing down very much even when pumping full flow. No matter how deep the pumps are set, they only lift from the actual water level. So if the water level in the well doesn’t pull down very much, both of those pumps are way oversized. This makes the pumps run in an up-thrust condition, which could be part of the problem.
I would test the pumping level in the well that still has a good pump, then consider the other well to have about the same pumping level. If the pumping level doesn’t pull down more than I think it will, you can probably reduce the size of those pumps by 50%. The smaller pumps would be less expensive to replace when needed, save a lot of energy, and still pump the same amount of water.
Also the check valves on each wellhead need to be removed. The pumps must have check valves on them at the bottom of the well, and those are the only check valves you need in the system. The check valves at the top of each well can cause water hammer, which could also be big part of your problem, as this water hammer can go down and shatter the down thrust bearings in the motors. The best place to install a CSV is where the check valves are, so remove the checks and install CSV’s in these locations.
Without changing the size of pumps, the high static levels and deep set pumps mean you will respectively have 251 PSI and 264 PSI back pressure before the CSV’s. You will need to use a CSV2W1.25T 50/120 Cycle Stop Valves on each well. The CSV’s will need to be fitted with what we call a “red seat” to be able to handle the high differential pressures. I would run the 5HP as pump #2, set the CSV to 65 PSI with a 50/70 pressure switch. Then I would run the 3HP as pump #1, and set the CSV at 70 PSI with a 55/75 pressure switch.
These CSV2W valves will have a minimum flow of 5 GPM each. So it would be best to always use more than 5 GPM when irrigating. But with a large tank or two, flow rates of less than 5 GPM will still not cycle the pump very fast and will work fine. If you could change the 3HP pump to a 2HP, we could do a minimum flow of 1 GPM, so neither pump will cycle as long as you use more than 1 GPM.
If you test the pumping levels and change out the pumps accordingly, we could use different CSV’s, have less differential pressure, and work at lower flow rates without cycling the pumps. If you stay with the same pumps, the special made CSV2W’s are the best for that application. These CSV’s will eliminate the pumps being destroyed by cycling. The additional backpressure from the CSV’s will keep the pumps form being destroyed by up-thrust. Removing the above ground check valves that are not needed will eliminate the water hammer, which could be destroying the down-thrust bearings.
Adding the CSV’s will give your pumps a good long life. Checking the pumping levels and sizing the pumps accordingly could greatly reduce your electric bill.
