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How Does a Hydropneumatic Water Tank Work?

Alex Burke

Tanks that use water and air under pressure are referred to as a hydropneumatic tanks, or pressure tanks. Compressed air is used in these tanks as a buffer or cushion that allows a surge-free delivery process. There are three functions for hydropneumatic tanks. The first is as part of a water delivery system set to deliver water in a preset pressure range. The second uses the pressure setting to monitor a pump from turning on too often. The third is to buffer or lower pressure surges, much like a power surge protector.

Functions Of Hydropneumatic Tanks

Components Of Hydropneumatic Tanks

Tanks vary in size and get very large. They're usually horizontal in design, with a capacity from about 2,000 gallons to 30,000 gallons or more. The system's needs determine the size of the tank. Sensors monitor the level of the water and pressure in the tank. These sensors are the automatic controls that operate the compressor. There are openings at either end of the tank; one is a tank access opening (where the water enters the tank), and at the other end is the pressure gauge and pressure switch (which controls the well pump). At the bottom of the tank is a drain opening and valves that are opened and closed to allow the regulated release of the water into the system. At the top is the air compressor and water level sensors, along with a pressure relief valve.

Adding More Air

There are two ways air can be added to a pressure tank: air volume control systems or air charging systems. Air is added when the water pump cycles. More modern pumps use the air volume control system, which contains an air compressor, pressure switch and a liquid level switch. A sensor connected to the liquid level switch drops down into the tank and monitors the water level. The pressure switch monitors the air pressure via a sensor. When air dissolves into the water, it causes the water level to rise and the air pressure to fall. The compressor triggers and pumps air into the tank when the water falls below the water level sensor and the air pressure falls below the setting on the pressure switch. A time delay prevents rapid cycling of the compressor.

Hydropneumatic Water Tanks

Common uses for hydropneumatic tanks are in well water processes. They can also be found in irrigation pumps and sprinkler pumps. Drawdown is the term used to describe the amount of water a particular system uses during a water cycle. This amount of water or drawdown must be known before a hydropneumatic water tank size can be chosen. Tanks can also have linings or bladders that separate the water from the inside of the metal tank.