How To Look At A House
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Why does my well pump turn on and off every time I use water?
Monday, October 1, 2018
When a well pump turns on every time a water-using fixture’s valve is opened, or if it turns on and off rapidly while the fixture is in use, that’s short cycling. It is typically caused by a water pressure tank that has lost it built-in cushion of pressurized air. The volume of air acts something like a spring: as the pump pushes water into the tank the volume of air is compressed, storing pressure energy so that the tank can supply water to a minor fixture like a bathroom faucet later on, as the air pressure alone forces water from the tank, for one to two minutes before the pump has to kick back on. Without an air cushion, the well pump would activate each time any faucet is turned or toilet flushed.
Well pump life is rated in on-off cycles—not hours of use—so short cycling significantly reduces the life of a pump and we check for it during an inspection. There is usually a faucet next to the well cap, and we open the faucet to see if the pump turns on immediately or too quickly. If there is background noise in the area it can be difficult to hear when a submersible pump (one that is suspended deep in a well) turns on, but you can easily feel the vibration in the casing when it starts up by placing your hand lightly on the well cap.
Two Types Of Pressure Tanks
There are two types of pressure tanks, and the fix for short cycling depends on which kind is installed. Older pressure tanks hold both the air and water together in the tank with no separating membrane. Air is absorbed into the water over time and the air pressure has to be periodically replenished. Adding compressed air at a schrader-type valve (like on a car or bicycle tire) located at the top of the tank fixes the problem in most cases.
Newer type tanks have a flexible bladder inside the tank separating the water from the air, so they do not gradually lose air. They also have an air fill valve; and most have the water in the bladder and the air in the surrounding space in the tank, but some manufacturers have the two reversed. When the bladder eventually deteriorates and ruptures it can cause a number of problems, one of which is short cycling. In some cases the bladder can be replaced, but it usually recommended to replace the entire tank—especially with an older tank that has corrosion.
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