How it Works
Standard residential well water systems operate within a 20 PSI differential. Controlled by a pump, pressure switch, and pressure tank all working in conjunction, the systems pump will turn on at the low end of the pressure range and off at the high end. Typical settings are 20/40, 30/50, or 40/60. It is critically important to install a properly sized pressure tank. Without the use of the proper size tank your well pump will cycle more frequently than recommended leading to frequent surges of excess heat. An undersized tank does not allow the pump to run for the time recommended by the pump manufacturer leading to shortened equipment life.
Pressure tanks operate off a principle called Boyle’s Law. Simply put, Boyle’s Law states that a gas (air) is compressible while a liquid (water) is not.
The job of a pressure tank is to provide a volume of air for the water to compress, building pressure in the system until a setpoint is reached that turns off the pump. Another function of the tank is storing water under pressure so that the pump does not need to run every time there is a demand for water.
Prior to the existence of pre-pressurized diaphragm or bladder tanks, galvanized, open-air tanks using some type of air volume control system to replace air in the tank were used. These tanks, having no means of pre-charge, require the system pressure start at atmosphere, approximately 14.7 PSI. This means that a larger tank is required to build pressure to the high end of the system settings to turn the pump off. The invention of a pre-pressurized expansion tank allows for a higher starting point, decreasing the size of the tank while delivering the same amount of water with less pressure fluctuation.