The purpose of the pump is to draw water from the well and push it through the distribution piping with sufficient force that the water overcomes the frictional resistance of the pipes and provides an adequate flow at fixtures.
There are three basic types of well pumps used for residential structures: submersible, jet, and piston. All three can be used for shallow or deep wells. The submersible pump, however, is most frequently used for deep wells. In shallow wells, the jet or piston pumping mechanism is not located in the water. It is located on top of the well. The water is drawn up to the pump by a suction action, not unlike drinking through a straw. A suction will result in a pipe immersed in a body of water when the pressure inside the pipe is reduced below atmospheric pressure (vacuum). Under ideal conditions, the maximum suction lift is 34 feet. However, because of pump inefficiencies and frictional resistance of the pipe walls, the practical limit of suction lift is 25 feet, which is used in defining a shallow well. A deep well, therefore, is one in which water is pumped from a depth that exceeds 25 feet.
Well pumps and their accessory equipment are usually very reliable. Nevertheless, all well-pumping systems require occasional repair or replacement. The projected life expectancy of a pump is seven to ten years, although many pumps run without trouble for twenty to thirty years.
These pumps are no longer in general use, although they might be found in older homes. Basically, they are motorized versions of the old hand pump. A motor drives the piston that alternately sucks water into the cylinder and then discharges it on every other stroke. In a shallow well, the pump (motor-piston assembly) is above the ground. In a deep well, the motor is above the ground, and the piston assembly is located in the well. Usually the motor is connected to the piston assembly by a belt and pulley. Inspect the belt for partially torn and frayed sections and adequate tension. Look for signs of leakage around casing joints and the piston rod. There should be none. An overall evaluation of any pumping system must include an inspection of the accessory equipment, which is discussed later in this chapter.
The jet pump consists of a jet assembly and a centrifugal pump. The centrifugal pump can be thought of as a small paddle wheel driven by a motor. As the wheel turns, it imparts energy to the water, increasing its velocity and pressure. A portion of the water discharging from the centrifugal pump is diverted to the jet assembly, which has no moving parts. However, it uses this recirculated water to perform two functions. It creates a suction that draws well water into the assembly and pushes this water back up to the centrifugal pump. After passing through the pump, some of the water is again rediverted to the jet assembly and the remainder directed to the plumbing system for distribution.
You can tell whether the pump is a shallow-well or deep-well jet pump by the number of pipes extending into the well. The basic difference between the two pumps is the location of the jet assembly. In a shallow-well jet pump, the jet assembly is built into the centrifugal pump casing and has only one pipe extending into the well. In a deep-well jet pump, the jet assembly must be located within the well (so that the suction lift does not exceed 25 feet). In this case, there are two pipes extending into the well. (See FIG. 13-11.) In areas where the temperature drops below freezing, proper weather protection of jet pumps is important. According to Gould Pumps, Inc., frozen pumps represent one of the most common reasons for pump replacement.
A submersible pump consists of an electrically driven centrifugal pump designed so that both the electric motor and the pump can operate under water. This pump is intended for placement directly in the well and is used primarily for deep wells. However, it can also be used for shallow wells. Water is drawn into the unit through screened openings located between the motor and the pump. A single discharge pipe is connected to the top of the pump and runs to the storage tank, which is usually found in the lower level of the house. When inspecting the pumping system, you will not see the pump, only the accessory equipment. (See FIG. 13-12.)
Because the electric motor is located in the well, in those areas where electrical storms are frequent, it is advisable to have a lightning arrester at the motor power supply. This will conduct high-voltage surges from the line to the ground before they enter and damage the motor. Submersible pumps have the advantage of quiet, dependable operation. They are relatively maintenance-free and are more efficient than jet or piston pumps. However, if a problem develops with the pump or motor, the entire unit must be withdrawn from the well.
For a private well-pumping system to provide water service comparable to that offered by a utility company, accessory equipment is needed.