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• The purpose of water storage or water pressure tanks on private well systems
• How to diagnose & correct short cycling "on-off" of the building water pump
• How to adjust the water pump pressure control switch
• Well pump & water tank diagnosis & repair procedures

This article describes the purpose of water storage and water pressure tanks, how they work, what goes wrong, how to fix it. Readers of this document should also see Water pump and pressure tank repair diagnosis & cost an specific case which offers an example of diagnosis of loss of water pressure, loss of water, and analyzes the actual repair cost. The illustration at page top is courtesy of Carson Dunlop, Inc. in Toronto.

PURPOSE OF WATER TANKS - What is the purpose of the water tank on building water supply systems

Private well and pump systems include a well (the water source), piping from the well to the building, a water pump, and a water tank to which building water supply plumbing is connected. Building plumbing fixtures (sinks, toilets, showers, tubs) are supplied with water from the building water supply piping, and drain into the building drain-waste-vent (DWV) system. When water is turned on at a fixture in the building, compressed air in the water tank pushes water out into the building water supply piping and thus to its plumbing fixtures. As water leaves the water tank, pressure in the tank drops. A pressure control switch, usually mounted on or near the water tank, senses the pressure drop, and at a pre-set "pump cut-in pressure" (typically 20 or 30 psi) the pressure switch turns on the water pump. The pump, located at the tank or perhaps in the well, pumps water to the building from the well, simultaneously re-pressurizing the water tank and providing water to the building. When water pressure in the pressure tank reaches the "pump cut-out pressure" (typically 40 or 50 psi) the pressure switch turns off the well pump.

If many fixtures are being run at once in the building, or if the water flow rate produced by the pump and piping and controls is a modest one, the pump may run continuously all while the fixture is being operated. More typically, if only one fixture is running and if the pump and well can deliver a high water flow rate, the pump may come on and off several times while the fixture is being run.

Why Air is Needed in a Water Tank

Air in the water tank acts like a spring or cushion which serves to smooth the delivery of water into the building as the pump cycles on and off. That's why I call this the water pressure tank rather than a water storage tank - though for most people these are the same device. This air cushion effect prevents the water from surging (much) at the plumbing fixture as the pump turns on and off as water is running during use of the fixture (such as a sink or shower). More important, this cushion effect prevents short-cycling of the pump on and off, which in turn prevents pump burnout or water pressure control switch damage which could occur if the system switches on and off too rapidly.

Why is a pressure tank with a buffer or spring or cushion of air needed? Water itself is not very compressible. Since a pump can usually pump faster than the flow of water out of a single faucet, as soon as the pump switched on, water pressure would build way up and the pump would immediately switch off. Water would not flow nicely from the tap. Instead it would come in a series of squirts. Worse, you'd burn up the water pump or pump control switch by this rapid cycling.

The air cushion in the tank acts like a big spring which is compressed by water pushed into the tank by the pump at the same time that water is also flowing out of the pump, tank, and piping system into the building to whatever faucet has been opened. So while water is running in a building served by a private well, part of the time the water flow is being maintained only by air pressure in the water tank, and part of the time the water flow is being boosted by the pump during its "on" cycle. And during the pump's "on" cycle, it is both pushing water into the house and re-pressurizing (by compressing) air in the water tank.

Use links just below or at the left of each of the pages at our website to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

If Your Water Tank is Not Working Properly See These Diagnostic Guides

WATER TANK REPAIRS
  CONTROLS & SWITCHES on WATER TANKS
  INTERMITTENT CYCLING WATER PUMPS
  SHORT CYCLING WATER PUMPS
  SHORT CYCLING DETECTION
  SHORT CYCLING CAUSES
  WATER TANK AIR LOSS SIGNS
WATER TANK AIR, HOW TO ADD
  WATER TANK AIR VOLUME CONTROLS
  WATER TANK AIR ADD AT AIR VALVE
  WATER TANK AIR IN BY DRAINING
  AIR HOW MUCH TO ADD
  AIR HOW OFTEN TO ADD

If You Need Help Diagnosing a Loss in Water Pressure or Other Pump & Well Problems See These Guides

WATER PRESSURE LOSS DIAGNOSIS GUIDE
  Water Pressure Intermittent
  No Water Pressure
  Water Pressure Tank Problems
  Water Pressure Tank Diagnosis
  Bad water pressure regulator
  Water pipe clog diagnosis
  Water pipe clog repair guide
  Making the "right" repair
  Typical Water Tank & Pump Prices

Water Tank Maintenance & Repair Chapter Index

Use links just below or at the left of each of the pages at our website to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

PLUMBING TOPICS
OIL TANKS
SEPTIC SYSTEMS
WATER PRESSURE REPAIR GUIDE & COSTS
WATER PRESSURE LOSS DIAGNOSIS GUIDE
  WATER PUMP PRESSURE CONTROL ADJUSTMENT
  WATER PUMP PRESSURE CONTROL REPAIR
WATER PUMPS & TANKS & WELLS
WATER PUMP CONTROLS & SWITCHES
PUMP TYPES & LIFE EXPECTANCY
WATER PUMP & TANK SAFETY
WATER SUPPLY & DRAIN PIPING
WATER TANK TYPES: WATER, OIL, EXPANSION, ALL
  CAPTIVE AIR WATER TANKS
  STEEL WATER TANKS
  BIG WATER STORAGE TANKS
  OPEN WATER TANKS
WATER TANK LIFE EXPECTANCY
WATER TANK REPAIRS
WATER TANK AIR, HOW TO ADD
WATER TANK PRESSURE CALCULATIONS
WATER TANK SIZE & VOLUME
WATER TANKS HOW THEY WORK
WATER TESTING
WELLS CISTERNS & SPRINGS
WELL LIFE EXPECTANCY

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