Private wells and well pump systems are beyond the scope of many home inspectors, but we all should understand the basic science behind well pressure tanks and know how to recognize a short-cycle problem.
Under normal conditions, a private well system utilizes a submersible centrifugal pump immersed in the water near the bottom of the well casing. The pump pushes water through a pipe in the well casing into a storage tank in the basement.
The storage tank or pressure tank limits the cycling of the pump by maintaining a cushion of air over water or air over a rubber bladder containing water.
Water use triggers the system
When someone in the household draws water, air expands in the tank, pushing more water out into the system. This reduces air pressure in the tank. As pressure in the tank approaches 40 psi, the pump switches on, refilling water in the tank and restoring the air pressure. When the air is compressed to about 60 psi, the pump turns off. This operation allows the home’s water flow to remain almost constant, as the 20 psi pressure change is rarely noticeable.
The pump is controlled by a pressure switch located on the piping near the pressure tank. Systems typically run between 40 and 60 psi, but can be set to a higher or lower pressure. Often, pressure is set with a simple spring and screw adjustment inside the pressure switch housing.
Loss of air cushion causes problems
Problems occur when the system loses its air cushion. In systems with no bladder, air is simply lost through contact with the water, with the air cushion disappearing over a period of several months. (Some systems have a floating disk that slows the loss of air.) Air loss can also occur with rubber bladder systems when the bladder fails.
Because there’s less air in the tank, the system kicks in repeatedly whenever someone draws as little as a quart of water. The pressure switch clicks on-off on-off. The pump may also turn on and off. With the pressure fluctuating so quickly, noticeable changes occur in flow and pressure.
This “short-cycling” will damage the pump. If you run water during a home inspection and notice any of these noises or quick variations in pressure, you should note this as a potential issue to be evaluated by a specialist. In this case, you are not doing a private well inspection but simply pointing out obvious issues that need further evaluation.
Some shallow well systems have a “jet” pump that sits on top of the well casing, and some older systems have a deep well jet pump. These systems also rely on a pressure tank to even the water pressure and flow. In recent years, sophisticated systems have become available, providing a variable-speed pump to vary the flow of water; these eliminate the pressure tank or use a very small pressure tank.
Tom Feiza has been a professional home inspector since 1992 and has a degree in engineering. Through HowToOperateYourHome.com, he provides high-quality marketing materials that help professional home inspectors boost their business. Copyright © 2015 by Tom Feiza, Mr. Fix-It, Inc. Reproduced with permission.