My family vacations at a summer-season cabin and we use a Southern S-250 shallow-well pump to draw water from a lake about 40 feet away. This type of water system, which includes a pressure tank, can have two major problems. First, a small leak on the inlet side of the pump will let air flow into the water stream and soon air will displace water in the pressure tank. If this happens, we find the leak and patch it or tighten fittings.
The second problem occurs because water in the pressure tank will absorb the air and lead to a water-logged tank. Turn on a tap and the pressure drops rapidly due to a smaller reservoir of air. The pump seems to run almost continuously. To solve this problem, we turn off the water to the cabin and drain the tank. When we turn on the pump again, the incoming water from the pump pressurizes a tank that starts out full of air.
(Remember: air will dissolve in water and over time, as the pump brings in more water, more air dissolves away. This water-log condition can take from weeks to months to occur, depending on pump use and ambient temperatures.)
Our system includes a clever, simple, mechanical control that helps eliminate the latter problem. A fitting in the center of the tank includes a port for a pressure gauge as well as a float valve, as shown in the simple drawing nearby.
When water in the tank reaches about mid level, it moves the float upward. In turn, the float arm actuates a small external valve that opens slightly as the water level rises above a preset level. The open valve lets a small amount of air into the inlet water stream. Thus, if the tank contains too much water and not enough air, the float-valve operates and admits more air. This simple control helps maintain the proper water-to-air in the pressure tank.
Newer pressure tanks overcome this problem by using a sealed air chamber and a flexible partition between the air and the water. But even after 46 summers, the Southern S-250 pump still works well and we’ve experienced few problems other than those described above. The air controller isn’t sophisticated, but it illustrates that some problems have simple yet elegant solutions. –Jon Titus