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
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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.
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
at WATER PUMP PRESSURE CONTROL ADJUSTMENT
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.
Just prevent short water pump cycling: You want enough air in
the tank that the pump stops short-cycling. Don't worry, you can't put in too
much air - as long as there is a pressure relief valve on the tank bottom you cannot damage the tank
by trying to put in excessive air pressure.
See SHORT CYCLING WATER PUMP.
Don't put too much air into a captive-air bladder-type water tank: we have had a number of reports of ruptured bladders in water tanks. If you put too much air into one of these tanks (the air is in the tank but outside of the bladder) the water pump wont' be able to push much water into the bladder and you'll get a short draw-down cycle. Conversely if you set the pump pressure too high on one of these systems, you might cause the water bladder to rupture inside the tank.
In general, bladder type water tank manufacturers recommend that the tank be empty of water when you set the air pressure in the tank to the specified psi. If you set the air pressure to the specified psi while there is water in the tank, the air volume will be incorrect (too small) and the water tank will not perform properly.
Don't blow up the water tank: If the tank does not have a pressure relief valve intended for water tanks installed on the tank bottom
or nearby to protect the tank from over pressure you should have one installed. Especially with systems using
a submersible pump capable of pumping to high pressure, this is an important safety device.
18 or 28 psi should be ok: If you are uncertain about whether or not the tank is protected from overpressure, you are
safe pumping the starting air pressure inside your water tank up to 18 psi if your water pump is operating in the 20-40 psi pressure range.
You can try starting at 28 psi before re-starting the pump if your water pump is set to operate in the 30-50 psi range. Some plumbers and well tank manufacturers instruct installers add air pressure to the water tank until air pressure in an empty tank is set to 2 psi below the preset water pump cut-in pressure. We discuss how to set the water pump cut in and cut out pressures
at WATER PUMP PRESSURE CONTROL ADJUSTMENT.
At least 30 seconds of water draw-down time is a reasonable minimum target: that is, with other water system pump and tank components operating normally, we want to be able to run at least 30 seconds of water at a nearby kitchen tap before the pump has to turn on. Longer draw-down cycles are better, up to the point of an excessive air charge.
Even without emptying water from a non-bladder type water tank we can often get things working satisfactorily by simply adding air until the tank drawdown cycle is sufficient.
Excess air will just be discharged: Provided that your water tank is one that does not use an internal bladder to keep water separate from air, if you have put more air into the
pressure tank than necessary, the excess air will simply squirt out of various
faucets the next time you run water and then the problem will go away.
See AIR DISCHARGE at FAUCETS, FIXTURES.
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
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Water Fact Sheet #3, Using Low-Yielding Wells [ copy on file as /water/Low_Yield_Wells_Penn_State.pdf ] - , Penn State College of Agricultural Sciences, Cooperative Extension, School of Forest Resources, web search 07/24/2010, original source: http://pubs.cas.psu.edu/FreePubs/pdfs/XH0002.pdf
Water pressure tanks - how to diagnose the need for air, how to add air, stop water pump short cycling to avoid damage - water storage water pressure tank safety.
WATER PUMP REPAIR GUIDE an specific case offers an example of diagnosis of loss of water pressure, loss of water, and analyzes the actual repair cost
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