A typical well pump system will have an 80 gallon pressure tank with a motor control box and pressure switch at the surface. When the pressure in the tank gets down to a certain point, the pressure switch closes, sends voltage to the control box, and the control box starts the well pump motor. The motor runs until the pressure reaches a certain high point, called the cut out, and the pump shuts off. This process repeats as necessary while you’re using water.
The pressure tank has an diaphragm with well water on one side, and air on the other. The air will compress between well pump cycles and is used to store the pressurized energy the well pump creates. When you open a faucet, the compressed air pushes the water out of the tank to the plumbing system. When the pressure gets low, the pump turns back on and rebuilds it.
Pressure tanks keep the pump from cycling on-off constantly, and allow the pump to properly cool when it does turn on. A well pump should run for a minimum of 1-1/2 to 2 minutes every time it starts, and this is accomplished with a pressure tank. A pressure tank also allows for shock absorption in the system – when valves close, pumps turn on/off, etc there’s hammering effects in the water, since it’s a non-compressible fluid, and the pressure tank will absorb this.
Newer pump systems use variable speed controllers, known as Variable Frequency Drives, or VFD’s for short. VFD’s allow the pump to run as an On Demand type system – the pressure starts to drop, the pump will start to run up to meet the demand. In the last 20 years they have become much more common, have a lot of more advanced features and reliable space saving appliances. VFD’s typically will allow for the use of much smaller pressure tanks than a typical system – 5-10 gallons is common. We still recommend larger tanks on higher flow VFD’s for pump impeller protection purposes.
Pressure tank failure is often the cause of pump failure – as the tank fills with water in the air chamber, the pump cycles shorten, the pump gets hot, and then the motor dies. It takes awhile for this all to happen and can be caught with periodic well checks or maintenance. If you notice sputtering water, air in the lines, the well pump rapid cycling, or any other major changes in the water system, you should call us immediately.