The water tank is a very important part of a household well fed water system. It provides water storage in order to protect
the well pump from damage due to constant cycling off and on. This allows for the pump to run for longer periods of time and
take breaks while the water is being used. This also provides much more even flow of water. The tank also can help with
water hammer too.
The water tank uses pressurized air to force the water out of the tank. This air also gets compressed as the tank fills
up with water. The pump gets operated by a control which has a "buffer" or differential. This allows the pressure to
fluctuate within a given pressure range.
The first water tanks were large galvanized metal tanks. The method for filling these tanks with air was to drain the water
out of them. A tank that is empty of water is also full with air. Then, when the pump is turned on, the full tank of air will
get compressed into a smaller pocket of air, with both the water and the air having the same pressures. When a faucet is
opened, the air pressure pushes on the water, forcing it out of the tank. There are still some of these types of tanks in
operation today, although most are beyond their life expectancy by now.
The problem with these tanks is that with no barrier between the air and the water, the air tends to slowly "dissolve" into
the water. This leaves the tank with a smaller and smaller air pocket.
The solution was like the tank shown above. It is a smaller tank with a rubber diaphragm in it. It is precharged with air
pressure on the top portion of the tank. This keeps the air and water separated.
The tank is still full of air when there is no water in the system. As the water pressure builds up, it pushes on the
diaphragm. The diaphragm will not move until the water pressure is greater than the air pressure. As the water pressure
builds higher than the air pressure, the air will compress, thus increasing and equalizing the air pressure.
The precharge tank pressure should be set 1-3psi below the cut-in(turn on) point of the pressure switch(the control). This
will leave the air pressure always lower than the water pressure, so that there will always be water in the tank.
Besides the tank itself, there is a standard "set up" kit that goes along with it.
Well Tank Kit
more details below photo
- 1. Pressure Switch
- 2. Check Valve
- 3. Drain Valve
- 4. 1/2" plug(Must be a relief valve!)
- 5. Pressure Gauge
- 6. Tank Cross
The first thing that needs to be said about this photo, is the lack of electrical connectors on
the wires. This is very important and can be dangerous. All building codes require connectors to be used.
This is a very dangerous part of a water system. It normally has a 220volt electrical circuit in it. The pressure switch
is the control for the water pressure. On most jet pumps, the pressure switch is set to turn on at 30psi and off at 50psi(30-50).
On submersible well pumps, the pressure is set for 40psi-60psi.
Setting the pressure can be quite tricky. It's easiest to use a 3/8" nut driver. There are different brands out there, but
we will be dealing with the "Square D pumptrol" brand/model. It will be necessary to run water and to be able to control the
water from the pressure switch area. A garden hose on the drain or opening a faucet and turning a main house valve(usually near the pressure switch) off and on
are the preferred methods.
There are 2 adjustment screws at the top of the switch with springs around them. The central screw raises the cut-on and
cut-off pressures at the same time. This keeps the difference between the two pressures the same. The screw on the left will
raise the cut-off pressure only. Clock-wise to raise, counter clock-wise to lower for both screws.
These pressures are set upon installation and should not ever have to be adjusted. If they need to be, it could be a sign
of a larger problem and should be checked by a professional. From the factory, they come with a 20psi differential already,
so the left screw almost never gets touched.
The basic idea of adjustment is to shut the water off to the open faucet(garden hose of main valve) and let the tank
pump up. Note where it shuts off at(this should never be more than 65psi max). Then open the hose to drop the pressure until
the switch snaps closed. Note where this cut-in pressure is.
If both pressures need to be adjusted, just use the central screw and check the pressures again. If just the cut-off
pressure needs to be adjusted, just use the left screw. If just the cut-in pressure needs to be adjusted, you will have to
use the central screw to adjust lower pressure, and then redo the cut-off pressure,
The check valve acts as a one way street for the water. It can come up the pipe and into the tank, but it is not allowed
to flow back down into the well. The system can generally be run without this check valve, but it required and very helpful
by separating the well drop from the tank setup. The check valve is 1" iron pipe size.
This is normally just a standard garden hose type drain valve. 1/2" iron pipe.
Years ago, this tap on the tank cross was plugged just like in the picture. This tap(1/2" iron pipe) is designed for a relief valve to be
installed. This protects the entire system from being overpressurized, which can cause serious damage and/or injury! For your
own good, please get one installed if you do not have one!
This is a 1/4" threaded iron pipe tap. The gauge generally reads from 0-100psi. They frequently go bad.
This is the main connection fitting for the tank. The cross is what has all of the taps for everything. There are a few
different kinds and sizes.
One common problem with the tank setup is the brass nipple that the pressure switch mounts to. It is 1/4" iron pipe and
because of its small size, and lack of water flow through it, it often becomes plugged up with rust and corrosion. This can
lead to many pressure problems from no water to high pressure to erratic pressure drops and changes.