Well Pump Installer common mistakes
Well Pump Installer · Understand the traps and how to avoid them.
When selecting a diaphragm pressure tank, compares only the tank's total nominal volume (for example, a 20-gallon tank) and assumes that entire volume is usable, instead of calculating drawdown from precharge and cut-in/cut-out pressures.
Tank catalogs list total volume prominently; the acceptance volume and drawdown are smaller and depend on the pressure settings, so candidates default to the big number.
What to do instead
Compute usable drawdown from the tank's acceptance factor for the actual precharge and pressure switch settings, and size the tank so drawdown covers the pump cycling limit; state the formula and assumptions on the exam.
Installs a second check valve at the pressure tank or service entrance 'for safety' while also keeping the pump check valve.
The candidate believes more check valves prevent backflow and does not recognize that trapped water between two checks can cause water hammer, airlocking, or false pressure readings.
What to do instead
Use one check valve directly above the pump or as specified by the pump manufacturer; do not add a downstream check valve unless a specific code or design requires it.
Chooses a replacement pump by matching the old pump's horsepower and advertised GPM without computing total dynamic head at the actual design flow rate.
Horsepower is familiar and easy to read from the nameplate, while TDH requires adding static lift, drawdown, pressure head, and friction; candidates skip the calculation under time pressure.
What to do instead
Calculate TDH as vertical lift plus drawdown plus pressure head (cut-out psi times 2.31) plus friction loss at design flow, then select the pump whose curve delivers design GPM at that head.
Sizes drop pipe friction loss using only the vertical pipe length, ignoring long horizontal runs, fittings, and the pressure head at the tank.
Friction tables are often applied to the vertical drop only, and equivalent length for elbows, tees, valves, and horizontal offsets is forgotten.
What to do instead
Add equivalent lengths for fittings, include horizontal offsets and elevation changes, and use the design flow rather than pump shutoff flow to look up friction loss.
Sizes submersible pump cable from the breaker ampacity or a generic ampacity table without applying the voltage-drop limit for the actual run length and motor current.
Cable sizing is confused with branch-circuit conductor sizing; the long run in a well creates voltage drop that can prevent motor starting.
What to do instead
Use the pump manufacturer's cable sizing chart or calculate voltage drop from motor full-load current and one-way length; keep the drop within manufacturer and NEC recommendations, often 5 percent or less while running.
Connects a three-wire submersible pump to an arbitrary control box or capacitor, or energizes a three-phase pump without checking rotation.
Control boxes look similar and the nameplate voltage and horsepower may match; rotation is invisible, so candidates assume any phasing works.
What to do instead
Match the control box, capacitor, and overload to the pump nameplate; for three-phase, bump-start and verify rotation by observing flow and pressure or by using a phase-sequence meter.
Sets the pressure tank air precharge equal to the pressure switch cut-in setting, or leaves the factory precharge without checking it.
The precharge is confused with the system operating pressure, and the factory charge may not match the design cut-in.
What to do instead
With the tank isolated and water pressure drained, set precharge to 2 psi below cut-in, such as 28 psi for a 30/50 switch, then verify drawdown and cycling.
Starts up a new installation with the discharge valve closed or without venting and priming, then judges pump performance from the first pressure reading.
Dead-heading a pump is used to get a quick pressure reading, and priming is skipped because the pump is submersible; trapped air and a closed valve distort readings and can damage the pump.
What to do instead
Open the discharge valve, vent air, run to a stable flow, and record pressure and flow at the design operating point; never leave a pump dead-headed.
On a no-water call, pulls or replaces the pump before checking the breaker, pressure switch contacts, control box, capacitor, and static water level.
The pump is the most visible suspect, and the diagnostic sequence is skipped under customer pressure.
What to do instead
Follow a checklist: verify voltage at the pressure switch and control box, check for a tripped breaker or GFCI, test the capacitor and overload, and confirm water level with a sounded well before pulling the pump.
Completes the wellhead without a sanitary seal or vent screen, or omits bonding and grounding of the pump motor and metal casing.
These details are treated as finish work; candidates focus on getting water flowing and do not connect them to code compliance and contamination risk.
What to do instead
Install a code-compliant sanitary seal and vent, bond metal casing and equipment, and verify the equipment grounding conductor is continuous before energizing.