Shallow-well jet losing prime at elevation
A homeowner at about 5,200 ft elevation has a 1/2 HP shallow-well jet pump mounted on a pad beside a 2-inch driven point well roughly 30 ft deep. When the system was installed, static water level was 18 ft below the pump and the unit delivered about 8 gpm with no trouble. Two dry summers later, static level is 23 ft and the level pulls down to near 24 ft while the lawn is running. The pump now loses prime, the gauge drops to zero, and the motor keeps running. The suction line is 1 1/4-inch with a foot valve, and the owner has already replaced the foot valve once. He wants you to install a larger jet pump, or a bigger suction line, to get his pressure back.
1. Explain why a bigger pump or larger suction line will not solve this, using the elevation.
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A shallow-well jet pump lifts water by creating a partial vacuum, so atmospheric pressure sets the ceiling. At 5,200 ft, atmospheric pressure is roughly 12.1 psi, which supports only about 28 ft of water column at perfect vacuum. Subtract the net positive suction head the pump needs at the impeller eye, plus friction loss in the suction line and foot valve, plus a margin for a worn nozzle or venturi, and the practical lift limit is closer to 20 ft at this elevation rather than the 25 ft people quote at sea level.
At a 23 ft static level with the water near 24 ft while irrigating, the pump is already past that limit. It cavitates, the jet stops entraining water, and prime is lost while the motor keeps running. A larger pump increases flow demand and makes cavitation worse; a larger suction line only reduces friction, which is not the controlling term. The limitation is physics, so the fix has to reduce the lift.
2. List the practical fixes and explain which you would recommend and why.
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The first option is a two-pipe deep-well jet with the ejector set below the pumping level, which moves the lift from the surface pump to a submerged jet and lets the surface unit push instead of pull. That requires a well that can accept the ejector and adequate submergence, so check the casing size and the point condition. The second option is drilling a new 4- or 6-inch well and setting a submersible below the drawdown, which is the most durable answer and also gets the pump out of the weather. A 2-inch submersible is possible in theory, but with a 30 ft deep well and a 24 ft pumping level you would have almost no submergence, so I would not trust it. A third option is a storage tank filled slowly, with a booster to serve peak demand.
I would price the new well with a submersible as the primary recommendation and the deep-well jet as the lower-cost alternative, and explain the 28 ft physical ceiling behind both numbers.
3. Your phone quote was for a like-for-like jet pump swap. The correct repair costs several times more. How do you handle the customer and the paperwork?
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Be direct early: the phone quote was based on replacing the pump, and the site data shows the pump is not the root cause. Show the customer the numbers, including the static level, the pumping level under load, the elevation, and the roughly 28 ft atmospheric ceiling, so the recommendation is evidence-based rather than a sales pitch. Then present the options side by side with installed prices and the expected life of each.
Put the revised scope in a written change order and get a signature before starting. Do not install another shallow-well jet just to honor the original quote; it will fail in the same way, and you will own the callback and the warranty claim. If the customer chooses the low-cost option, note on the invoice that the lift limitation was explained and that performance during dry periods is not guaranteed. Also raise the permit question for a new well before any drilling is scheduled.