Pumps, Pumping Systems, and Water Storage
What the exam tests
Pump and storage questions test sizing, installation, and control logic: total dynamic head, pump curve, pressure tank, and the electrical and mechanical details that keep a residential system from short-cycling.
Core concepts
- Total dynamic head (TDH) = vertical lift from pumping water level to discharge + drawdown + required pressure head + friction loss. Convert psi to feet by multiplying by 2.31.
- A submersible pump is set above the screen or open interval, not below it, and above the anticipated drawdown with a safety margin. A jet pump is limited by suction lift and is used for shallow settings.
- The pressure tank provides drawdown volume so the pump does not cycle on every tap. Precharge is set about 2 psi below cut-in; a bladder tank does not need an air-volume control.
- Check valves hold prime and protect the pump from backspin; more than one check valve in a deep setting can cause water hammer.
- A constant-pressure system varies pump speed with a VFD and needs a pressure sensor and minimum-flow protection.
Worked example
Static water level 60 feet, drawdown 20 feet, 40 psi required at the house (92 feet), friction loss 10 feet. TDH = 60 + 20 + 92 + 10 = 182 feet. At 10 gpm, select a pump whose curve delivers about 10 gpm at 182 feet, not a pump that delivers 10 gpm at shutoff. Check that the motor horsepower is adequate at the actual operating point and that the pump is set at least 10 feet above the screen.
Traps
Sizing by house size or tank gallons instead of TDH and demand. Setting a pump below a fractured interval and pumping sand. Forgetting that a 30/50 switch requires a different tank precharge than a 40/60 switch. Ignoring friction in a long lateral - it can add more head than the vertical lift.