How Much Air to Add to a Water Pressure Tank

  • WATER TANK AIR HOW MUCH TO ADD - CONTENTS: How to add the correct amount of air back to a water pressure tank to stop short cycling and get good water pressure and flow. How to diagnose & correct short cycling "on-off" of the building water pump. Well pump & water tank diagnosis & repair procedures
  • POST a QUESTION or READ FAQs on how much air you should add to a water pressure tank - how to figure out the right amount of air to add and how to tell when enough air has been added to the water tank

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When charging a water pressure tank, how much air should be added?

This article describes how to determine how much air should be added to a building water tank in a building water supply system where a private well is the water source and the well tank is not a bladder type or "captive air" tank.

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HOW MUCH AIR TO ADD - How Much Air is needed in the water pressure tank?

These comments only apply to methods 1 and 2 for adding air to a water pressure tank.

1 (using an air volume control) and

2 (using an air valve) for adding air to a water tank, discussed above.

Method 3 for restoring the air charge to a water pressure tank (draining water out of the tank) is so simple you just don't care about this question.

Here we are discussing adding air into a water tank, up to some starting pressure (the pump is turned off during this procedure) so that the water pump itself doesn't have to work too hard. Don't confuse the air pressures we discuss here with the water pressures we discuss

Some basic concepts about water tank air pressure: if the air pressure in the water tank is higher than the pump pressure control cut-in pressure, in a captive-air water tank the pump can't turn on.

In a "glass lined" bladderless water tank this problem will self-correct - when a nearby faucet is opened excess air will simply gush out of the faucet at the end of the drawdown cycle. If the air pressure in the water tank (when the tank is empty) is much below the pump pressure switch cut-in pressure, the volume of water that can be drawn out of the water tank will be reduced and the system will not perform properly.

Photograph of a moldy water pressure tank

Water tank condensation marks: If you look at an older pressure tank you can usually see a darker or even rusted color at the bottom portion of the tank.

[Click to enlarge any image]

The top edge of this colored area marks the normal air-water boundary in the tank. (Condensation on the water-filled part of the tank causes this corrosion or darkening.) In this photograph the black mold and debris stains on the lower portion of the water tank probably show the usual levels at which water has been maintained in the tank.

So if you've pumped air into the tank and later you see that the top of the area of tank covered by condensation is about where this line is, you're in business. If you see condensation occurring 2 or 3 inches from the top of the tank you need to add more air.

We used to put in enough air to give a minimum of 30 seconds of water running before the pump came on but this number varies widely depending on pump power and on how fast an individual fixture runs. So ignore air quantity advice based on time except to watch out for real short-cycling as described earlier.

Readers of this document should also
see WATER TANK BLADDER PRESSURE ADJUSTMENT where we describe adjusting air pressure in a bladder type water tank to factory specs.

Readers of this document should also
see WATER PUMP REPAIR GUIDE for a 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.


Continue reading at WATER TANK AIR HOW OFTEN TO ADD or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see AIR VOLUME CONTROLS, WATER TANK used on bladderless water pressure tanks


Or see WATER TANK BLADDER PRESSURE ADJUSTMENT if your water tank uses an internal bladd


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