Well Pump & Pressure System Glossary

• A
• B
• C
• D
• E
• F
• G
• H
• I
• J
• L
• M
• O
• P
• R
• S
• T
• U
• V
• W

A

Air-over-water tank

An older style of pressure tank with no membrane between the air and the water. The air slowly dissolves into the water, so the tank needs its air replenished or it becomes waterlogged. See types of well tanks.

Amp draw (running current)

The current a pump motor draws while it runs, measured with a clamp meter and compared with the manufacturer's table. Too high points to a binding pump or an electrical fault; Franklin Electric notes that low amps may be caused by a worn pump.^[1] A professional measurement.

B

Backspin

A pump turning backward as water falls back down the pipe after the pump stops — the result of a missing or failed check valve. Franklin warns that starting a motor while it is backspinning can break shafts and damage impellers.^[1]

Bladder tank

A pressure tank in which the water is held inside a flexible bag, with the air charge around it. Works on the same principle as a diaphragm tank.

Bound pump (sand-locked pump)

A pump that is powered but cannot turn, usually because sand has jammed it. Franklin says amp readings will be 3 to 6 times higher than normal until the overload trips.^[1] See breaker keeps tripping.

Breaker (double-pole)

The switch in your electrical panel that protects the pump circuit's wiring. A 240-volt pump circuit uses a double-pole breaker: two handles tied together. It is separate from the motor's overload protector.

C

Capacitor (start and run)

An electrical part that helps a single-phase motor start (start capacitor) or run more efficiently (run capacitor). On a three-wire pump they live in the control box. Capacitors can hold a charge after the power is off.

Casing

The steel or plastic pipe that lines the well and keeps the hole open. Its inside diameter decides which pumps fit; standard residential submersibles are 4-inch units.^[1]

Check valve

A one-way valve that stops water from flowing back down the well when the pump stops. Franklin calls for one within 25 feet of a submersible pump if the pump has none built in, and says swing-type check valves should never be used with submersibles.^[1] See check valve symptoms.

Constant-pressure system

A pump controlled by a variable-speed drive that speeds up and slows down to hold one pressure, instead of cycling between cut-in and cut-out. See constant-pressure systems.

Control box

The above-ground box that holds the starting parts for a three-wire submersible motor: a start capacitor and relay, and on some sizes overload protectors and run capacitors.^[1] Two-wire pumps don't have one. See well pump control boxes.

Cut-in pressure

The pressure at which the pressure switch turns the pump on — the first number in "30/50" or "40/60".

Cut-out pressure

The pressure at which the switch turns the pump off — the second number. Pentair says it should be at least 5 psi below the pump's maximum (dead-head) pressure.^[2]

Cycle

One complete pump run: from cut-in, through filling the tank, to cut-out. Counting and timing cycles is the simplest health check on a well system — see the monthly cycle check.

D

Dead head (shut-off pressure)

The highest pressure a pump can produce, reached when it runs with no water flowing. A switch set above it means a pump that never shuts off. Pentair warns against running a pump against a closed discharge to test it.^[2]

Diaphragm tank

A pre-pressurized tank in which a fixed rubber diaphragm separates a sealed air charge from the water. A common residential design.

Differential

The gap between cut-in and cut-out — 20 psi on a standard switch. A narrower differential means less water per cycle and more pump starts.

Differential nut

The small adjusting nut on a two-nut pressure switch. It changes the cut-out only.^[3] Compare range nut.

Drawdown (of a tank)

The water a pressure tank delivers between cut-out and cut-in — far less than its total volume. A 40-gallon tank on a 40/60 switch delivers about 10 gallons by the calculation method published in The Driller.^[4] See drawdown by tank size.

Drawdown (of a well)

How far the water level in the well falls while the pump runs: the difference between the static level and the pumping level. The same word, a different meaning.

Drop pipe

The pipe inside the well that carries water from a submersible pump up to the surface, and from which the pump hangs.

Dry running

A pump operating without water. Pentair warns that running a jet pump dry can overheat it and damage the seal.^[5]

E

Ejector (jet, injector)

The nozzle-and-venturi assembly that gives a jet pump its name. On a shallow-well jet it is part of the pump; on a deep-well jet it sits down in the well.

F

Flow rate

How much water a pump delivers, in gallons per minute (GPM). A pump's flow is only true at a given head: the more it has to lift and pressurize, the less it delivers.

Flow sleeve (flow inducer sleeve)

A tube fitted around a submersible pump and motor so that incoming water has to flow past the motor and cool it. Franklin requires one where the well would not otherwise provide enough flow past the motor.^[1]

Foot valve

A check valve with a strainer at the bottom of a jet pump's suction pipe. It keeps the pipe full of water so the pump stays primed. See jet pump loses prime.

Friction loss

Pressure used up pushing water through pipe, fittings and filters. It is part of the pump's total head.

G

GPM

Gallons per minute, the unit of flow.

H

Head (total dynamic head)

Everything the pump works against, expressed in feet: the lift from the pumping level to the surface, friction in the pipes, and the pressure delivered. Pressure converts at 1 psi = 2.31 feet of head.^[6] See total head, simply.

Horsepower (HP)

The motor's rated output. One horsepower is 746 watts at the shaft; the motor draws more than that from the wall — Franklin lists its 1 HP submersible motor at 1,210 watts at full load.^[1] See electricity use.

I

Impeller

The spinning wheel inside a pump that throws water outward to create pressure. Submersible pumps stack several. Sand wears them.

Insulation resistance (megger test)

A test made from the surface, with the power disconnected, that shows whether the motor windings or cable have lost their insulation. Franklin's guide for a motor in the well: 2.0 megohms or more reads like a new motor, 0.5 to 2.0 is a motor in good condition, and below 0.5 means insulation damage.^[1] Professional work.

J

Jet pump

A pump that sits above ground and draws water up by suction. Shallow-well jets are limited to water within about 25 feet; Pentair says a deep-well jet package may be needed beyond that.^[5] See submersible vs. jet pumps.

L

Locked-rotor amps

The current a motor draws at the instant it starts, or when it cannot turn. Franklin lists its 1 HP, 230-volt three-wire motor at 41.8 amps locked-rotor against 8.2 amps running.^[1] It is why generators for well pumps are sized so generously.

Low-pressure cutoff

A feature on some pressure switches that shuts the pump off if pressure collapses, so it cannot run dry. It has a small lever used to restart the pump. See the low-pressure cutoff lever.

M

Megohmmeter (megger)

The instrument used for an insulation resistance test. Franklin's readings are based on a meter with a 500-volt DC output.^[1]

O

Overload protector

A heat-sensitive device, inside the motor or in the control box, that shuts the motor off when it overheats. Unlike a breaker, on many motors it resets by itself once it cools — which is why a pump can stop and restart with nobody touching it.

P

Pitless adapter

A fitting in the side of the well casing, below the frost line, that connects the drop pipe to the buried line running to the house. It lets the pump be pulled from above without digging.

Precharge

The air pressure in a pressure tank when it is empty of water. Amtrol specifies 2 psig below the pump's cut-in — 38 psig on a 40/60 switch.^[7] See pressure tank precharge.

Pressure gauge

The dial at the tank that shows system pressure in psi. It is the single most useful diagnostic tool a well owner has.

Pressure switch

The switch at the tank that senses water pressure and turns the pump on at cut-in and off at cut-out. See pressure switches and controls.

Pressure tank

The tank that stores water against a cushion of compressed air so the pump doesn't have to start every time a faucet opens. See well pressure tanks.

Prime

The water that must fill a jet pump and its suction pipe before it can pump. A pump that has "lost its prime" is spinning in air. Submersible pumps sit under water and don't need priming.

psi

Pounds per square inch, the unit of pressure. Gauge pressure (psig) is what the dial shows; absolute pressure adds the atmosphere's 14.7 psi at sea level and is what tank calculations use.

Pump curve

The manufacturer's chart showing how much water a pump delivers at each head. It is how a pump is matched to a well.

Pumping level

The water level in the well while the pump is running. It is lower than the static level, and it is the level the pump actually lifts from.

R

Range nut

The large adjusting nut on a pressure switch. Turning it clockwise raises cut-in and cut-out together.^[3] See adjusting a pressure switch.

Recovery (well yield)

How quickly water flows back into the well as it is pumped out. A pump that delivers more than the well yields will draw the water down to its intake.

Relay (starting relay)

The part in a control box that connects the motor's start winding for the first moment of each start, then drops it out once the motor is up to speed.

Relief valve

A safety valve at the tank that opens if pressure climbs too high — for example, if the switch fails to stop the pump. Amtrol requires one on its tanks, set to open at 125 psig or more.^[7] Never cap or plug it.

S

Sensing nipple

The short ¼-inch pipe that connects the pressure switch to the system. When it clogs with sediment, the switch can no longer read the pressure. See clogged sensing port.

Service factor

A multiplier showing how far above its rated horsepower a motor may be loaded. Franklin lists 1.6 for its ½ HP and 1.4 for its 1 HP 4-inch motors.^[1] "Maximum load" watts and amps are measured at the service factor.

Short cycling

A pump starting and stopping too often. Franklin asks for at least one minute of running per start.^[1] See short cycling.

Static water level

The water level in the well at rest, with the pump off.

Submersible pump

A pump and motor in one long cylinder that hangs in the well below the water and pushes water up. The usual choice for drilled wells.

Surge arrestor

A device that diverts voltage spikes from lightning or the power line away from the motor. Franklin's installation checklist calls for a dedicated one on submersible motors.^[1]

T

Tank tee

The multi-port fitting at the base of the pressure tank that carries the pressure switch, the gauge, the relief valve and a drain valve.

Three-wire motor

A submersible motor whose starting parts are in an above-ground control box. It has three power conductors plus a ground. See 2-wire vs. 3-wire.

Two-wire motor

A submersible motor with its starting parts built in. Two power conductors plus a ground, and no control box.

U

Upthrust

An upward force on a pump's impellers and shaft when it starts with no pressure above it — the result of a missing or leaking check valve. Franklin says repeated upthrust can cause premature failure of both pump and motor.^[1]

V

Variable-frequency drive (VFD)

An electronic controller that changes a motor's speed. It is the heart of a constant-pressure system.

Voltage drop

Voltage lost along a wire. Long runs of undersized cable can leave a pump motor short of voltage when it starts; Franklin requires the supply to stay within 10% of the motor's rating.^[1]

W

Water hammer

A bang in the pipes when moving water is stopped suddenly. On a well system Franklin traces it to a check valve set more than 30 feet above the standing water level, or a lower check valve that leaks, and says the system should be shut down and the installer contacted.^[1]

Waterlogged

Said of a pressure tank that has lost its air cushion and filled with water, so it can no longer deliver water between pump starts. The usual cause of short cycling. See what waterlogged means.

Well cap (sanitary seal)

The cover on top of the well casing. The EPA lists a broken or missing well cap among the things to inspect for.^[8]

Missing a term? Tell us and we'll add it. Every guide on the site is listed in all guides.