The purpose of the pitless adapter in a water well is to keep pumped water below the freezing point or frost line and to provide service access to the well pump and equipment without a well pit. The pitless adapter is a special fitting that seals the passage cut into the well casing and connects the horizontal pipe, which carries water from the well, with the well pipe. When removing a well pump, the point of disconnection is the adapter.
Placement of the pitless adapter depends on the depth of the frostline, which varies by climatic region from 7- to 8-foot depths in colder and 2- to 3-foot depths in milder climates.
Spool-type pitless adapters include two to four rubber "O" rings, which are a bit larger than the inside diameter of the well casing. Roadside rest areas and other public facilities with well casings 6 inches or larger use spool-type adapters. Another type of pitless adapter has a pipe union as the connect/disconnect point with an attached mechanism for separating the two parts of the connection. Some states mandate the use of "clear case" or "fail safe" pitless adapters, which keep the well casing free of obstruction when the adapter is not connected.
Most pitless adaptors are brass and do not require replacement. Steel adaptors may require replacement.