Short-Cycling Pump and a Leaking Pitless Adapter
A 4-inch steel-cased well is 180 feet deep with static water at 40 feet and a pumping level of 95 feet at 12 gpm. A 1.5-hp submersible pump is set at 160 feet. The pitless adapter is about 5 feet below grade, and the buried line runs 70 feet to a pressure tank with a 20/40 psi switch. The homeowner reports the pump starts and stops every 30 seconds, the pressure gauge jumps, and water pulses at the tap. There is a wet spot at the casing after rain and a slight sulfur smell. The installer replaced the pressure switch and checked the tank air charge, but the cycling continues. The wellhead is a plain slip-on cap with a rope hole, and the casing is 6 inches above grade. Frost depth is 48 inches.
1. What is the most likely cause of the 30-second cycling, and how would you isolate the pitless adapter, check valve, and pressure tank before replacing the pump?
Read the worked answer
The cycling is too fast to blame on the pump motor alone. The first test is to isolate the pitless adapter with a test plug at the casing and observe pressure decay. If pressure holds, the pitless and buried line are not the source; if it drops, the pitless seal, O-ring, or discharge line is leaking. Next, check the pressure tank for a waterlogged bladder or incorrect air charge, because a small tank with a 20/40 switch can cycle rapidly even when the pump is healthy. Then check the check valve and drop pipe for backflow: a leaking check valve lets water drain back into the well and causes the pump to restart immediately. The wet spot after rain and sulfur smell point strongly to a pitless adapter seal that is admitting surface water, which can also affect water quality. The sequence matters because replacing the pump before isolating these components may leave the real defect in place.
2. Which wellhead and pitless details violate completion requirements, and what corrections are needed before restart?
Read the worked answer
The plain slip-on cap with a rope hole is not a sanitary well cap; it allows insects, surface water, and debris to enter the casing. It should be replaced with a watertight, vented well cap that seals the casing and includes a screened vent. The casing is only 6 inches above grade, which is too low in most Iowa settings and makes flooding and surface-water entry more likely; it should be raised to the required height, commonly at least 12 inches above grade, with the ground sloped away. The pitless adapter is 5 feet below grade, which is below the 48-inch frost depth, so depth is not the defect; the seal and O-rings are. The pitless must be rated for the casing, correctly seated, and watertight. The wet spot and sulfur smell should be investigated as a seal failure, not masked with more soil. The electrical conduit and vent must be screened and arranged so water cannot run into the casing.
3. What pump damage risks arise from the cycling and the 160-ft setting, and what operating changes would you recommend?
Read the worked answer
Frequent cycling overheats the motor, stresses the start capacitor and relay, and can shorten the pump life. The 160-foot setting gives about 65 feet of submergence above the 95-foot pumping level, which is adequate at 12 gpm only if the pumping level is accurate; if the well yields less and the level drops toward the pump, the motor loses cooling and may cavitate. Before changing the setting, verify the pump curve, actual drawdown, and amp draw. A larger pressure tank or a cycle-stop device can reduce starts, and the pressure switch differential can be widened if the system allows. Check the check valve and drop pipe for leaks, because a leaking check valve causes both rapid cycling and backspin. Add low-water protection if the well yield is uncertain, and do not set the pump so close to the bottom that sand or sediment is pulled in. The pump should be restarted only after the pitless leak and wellhead deficiencies are corrected.