Pressure Tank Maintenance

[Cary Austin]

Since this question gets ask so often.  I thought I would start a thread on how to check the air in a pressure tank.

If your pump kicks "on and off rapidly", water pressure in the house is not good, lights in the house "flicker" when water is being used, breaker trips occasionally, or you just want to check the "air pressure in the tank" read the following.

All pressure tanks must have the correct amount of air to water ratio.  The air acts like a spring to push water out of the tank when a tap is opened.  The pressure will decrease as the water is pushed out of the tank, until the pressure drops low enough for the pressure switch to start the pump.  There is usually a 20 pound bandwidth between pump start and pump stop, such as on at 40 PSI and off at 60 PSI.

Once the pump starts at 40 PSI, the tank is refilled and the air in the tank is again compressed until the pressure reaches 60 PSI and the pump shuts off.  The amount of water that the tank will express as the pressure lowers from 60 to 40 PSI, is called "draw down".  Most of the volume of a pressure tank is filled with air.  An 80 gallon size tank only holds 23 gallons of water, and a 20 gallon size tank only holds 5.35 gallons of water.  

There are basically two types of pressure tanks, which are "Hydro Pneumatic" and "Bladder or Captive Air tanks."

[Cary Austin]

Hydro Pneumatic means air over water.  These type tanks usually have two pipes, a pipe on one side comes from the well,  and a pipe on the other side of the tank goes to the house.  These are plain tanks with nothing separating the air from the water.  Since air is touching water inside the tank, the air will mix with the water and be taken out with the flow of water.  These type tanks require some kind of air make up system to continually replace the air.  The most common air make up system is the bleeder orifice style.  A bleeder orifice is a fitting that goes down in the well about 5' below the surface.  This fitting has a small hole that is covered with a flap or a ball from the inside of the pipe when pressure is applied.  This keeps the bleeder orifice closed when the pump is running and there is pressure in the pipe.

There must always be a one way check valve on a submersible pump.  The bleeder orifice works in conjunction with an additional check valve that is installed above ground before the pressure tank.  On the inlet side of this check valve there should be a "schrader valve".  A "schrader valve" looks like the valve stem on a car tire.  When the pump shuts off, the above ground check valve closes and keeps the pressure in the pressure tank from going back down the well.  As soon as this above ground check valve closes, the pressure in the pipe down hole will be at low or no pressure, and the ball or flap in the bleeder orifice will open.  As water drains out of the bleeder orifice into the well, the schrader valve will allow air to be sucked into the pipe.  The water in the pipe will then drain down to the level of the bleeder orifice in the well, so all the pipe from the bleeder orifice to the schrader valve will be filled with air. .

When someone uses water from the other side of the tank, the pressure will drop from 60 to 40 PSI as the amount of water available from the draw down in the tank is being used.  When the pump starts at 40 PSI, the pressure in the pipe closes the bleeder orifice and the air that was in this top section of pipe is forced through the above ground check valve and into the pressure tank.  Each time the pump cycles on, more air is injected into the pressure tank.  If too much air is injected into the tank, soon air will start to come out the faucets and will blow a glass out of you hand or blast air at you in the shower.  Therefore another device called an "Air Volume Control" or AVC is used to bleed any excess air out of the tank.  The AVC is usually installed about half way up the side of the tank through a 1 ½ inch fitting.  Sometimes the pressure gauge or even the pressure switch will be attached to the AVC as well.  Although sometimes the pressure switch and gauge are attached to the pipe going into the tank, and the AVC will only have a small brass fitting sticking out of it.

Inside the tank on the AVC there is a float on a 12" rod that drops when the water level is low.  When this float is in the low position, the AVC allows excess air out of the tank through the little brass fitting outside the tank.  When the float on the AVC is up, this little brass fitting is closed so as not to allow water out of the AVC.  All four of these items, the bleeder orifice, the above ground check valve, the schrader valve, and the AVC must be working properly for the air make up system to function.  If the AVC is not working, you will get air in the faucets in the house.  If either the bleeder orifice, above ground check valve, or the schrader valve are not working, the tank will become "waterlogged" and the pump will cycle on and off very rapidly.

There are also other types of air make up systems that use a air injector or "micronizer", or a small air compressor to add air instead of a bleeder orifice system.  These are not as common and so we won't discuss them here.

To manually add air to a "hydro pneumatic" type system you should first shut off power to the pump.  Opening a faucet will not completely drain the tank as it is like holding your finger over a straw full of water.  You must remove a fitting half way up the tank or higher to allow air in.  The air will gurgle as the tank slowly drains of water.  You can also use a compressor to add air at the schrader valve while a faucet is open.  This will force air in, and water out of the tank without needing to remove any fittings.  Once all the water has been blown out of the tank, or has been drained out of the tank, replace any fittings that were removed, close the faucets and restart the pump.  Having to do this means your air make up system is not working and should be repaired, or this maintenance procedure that should be done very regularly.

Hydro pneumatic tanks are one of the oldest style pressure tanks.  These type tanks are now only used in certain areas where water quality requires them.  Mixing air with water in these type tanks is used to reduce "rotten egg" smell from sulphur or other things in the water.  If your system does not require mixing air with water for water quality purposes, then a bladder type pressure tank can eliminate several moving and wearable parts, which can make the system more reliable and require less maintenance.

[Cary Austin]

One of the most common types, these tanks use a bladder or a bag to separate the water from the air.  These are called "bladder tanks", "bag tanks",  "captive air tanks", or "pre-charged tanks".  These tanks will only have one opening in the bottom, as the water goes in and out the same pipe. These type tanks will feel light or empty when shook back and forth, as there is only a small percentage of water at the very bottom, and the rest of the tank is filled with air.  Bladder tanks do not require an air make up system or an above ground check valve, which eliminates four wearable parts from the old style Hydro Pneumatic style systems, and makes bladder tanks more reliable and have less maintenance.  

The air "pre-charged" is separated from the water by the bladder.   This air cannot mix with the water, and therefore should not be able to get out of the tank.  Air is made of very small molecules and can escape through the rubber bladder or even through the steel shell of the tank. Air can also escape through the schrader valve on top of the tank, if the valve stem core is leaking or the cap is not tight.   Although it should take may years for the air to escape from a good bladder tank.  I have seen bladder tanks that are 25 years old or older, that are still within a couple of pounds of the original pre-charge pressure.

A disadvantage of bladder type tanks is that cycling on and off causes the bladder to go up and down continuously.  The bladder flexing back and forth will cause the rubber bladder to break, similar to bending a wire back and forth until it breaks.  Once this bladder is busted, the tank must be replaced.  Rapid cycling on and off is usually the first sign of a broken bladder.  

To check the air pressure in a bladder tank the power to the pump must be turned off.  Then a faucet should be opened until water stops coming out of the tap.  While the pump is off and the faucet is still open, you can check the air pressure at the schrader valve on top of the tank.  You will need to use a car tire pressure gauge on the schrader valve.  The air pressure in the tank should be 2 to 10 PSI below the "start" pressure of the pump.  IE; with a 40/60 pressure switch, the air pre-charge in the tank should be no higher than 38 PSI and no lower than 30 PSI.  Use an air compressor to pre-charge the tank to the correct pressure.  If the air is coming back out of the open faucet, then the bladder is busted.  If while holding the valve core down on the schrader valve, water comes out, the bladder is busted.  If the schrader valve will not accept air from the compressor, the bladder is most likely busted.

Sometimes you can add air to a tank with a busted bladder and it will work temporarily.  Usually the busted bladder will eventually settle over the water opening in the tank and no water will come out.  Even if the tank continues to work without causing a rapid pump cycle, the water on top of the busted bladder can become stale and/or rust a hole in the un-coated air side of the tank.  A tank with a busted bladder should be replaced as soon as possible.

When replacing a tank with a busted bladder, many times the bladder pieces have sealed over the water inlet connection.  In this case, even after removing the inlet piping from the tank, the water cannot get out and the tank will be extremely heavy.  The only way to empty the water from the tank, is to punch or drill a hole in the side of the tank to let the water out.  This can make a big mess in your well house but, an 80 gallon tank that is full of water because of a busted bladder can weigh over 700 pounds.  This can make it impossible to haul the tank out of the room, if you do not punch a hole in it and let the water out first.

Yearly or periodic inspections of your air pre-charge in the tank can help you maintain the correct air pressure.  This will greatly extend the life of the tank by eliminating over flexing of the bladder.  The best way to increase the life of a bladder tank, is to reduce the amount of pump cycling.  A larger pressure tank will reduce the number of cycles per day, or a constant pressure valve such as a Cycle Stop Valve can drastically reduce the number of cycles per day.  This will greatly increase the life of a bladder in a tank, as well as increase the life of the pump itself.