Air Release Valves

Air release valves are used to release the air from pockets that are formed in pipelines. Due to the basic nature of fluid phases, air pockets will form at the high points of a fully pressurized pipeline. Air release valves are necessary for pipeline efficiency and to protect against water hammer. Air in the water lines can cause many problems, the main one speeding up the process of corrosion (Causing high costs in the maintenance of the pipeline). A reduction of flow is also created by air that has been trapped at the bends, tees and other fittings in the system. Flow can even stop due to an “air lock” in the water line. This often happens in chemical feed lines at a water plant. If air release valves are not installed, uncontrolled air releases may occur, causing pressure surges in the system, which can increase the chances of hazards from cavitation. Alternatively, if air is left in a water main, it will eventually cause customers’ meters to read improperly, thus charging the customer for air that is going through the meter, and not water.

The “universal” type of Air release valves are designed to allow the automatic discharge of large amounts of air from the water main while it is being filled, and also to allow air to enter the water main when the water line is being emptied. A 3rd function is to allow the air to escape the water main when it is in operation and under pressure. This is achieved by means of buoyant floats, which activate a seal in large and small orifices in one integral body casting. As the liquid in the pipe system rises into the valve, air escapes through the large orifice to the atmosphere. Liquid entering the valve raises the float system, which causes a seal to close the valve.

If accumulating air rises into the valve while the line is in operation and under pressure, it will displace the liquid at the top of the valve body and the float will drop as the liquid recedes. As this occurs, the pressure valve will open, permitting the escape of the accumulated air, after which the liquid level will rise and the valve will close.

When one considers the difficult functions which have to be achieved by Air valves ie the controlled release and intake of air under vacuum, low pressure and high pressure conditions, many problems arise for designers. These problems are early leaking seals, too small automatic orifices leading to early clogging, low pressures preventing proper seals being formed, fast closure of the air valve causing water hammer, premature closure due to high air flow and many more. ARI, the largest manufacturer of air valves in the world and promoted by Ultra Control Valves, have solved all these problems and is today the only known air valve which comes with 10 year guarantee against seal leakages, and has become known as the zero maintenance air valve. ARI have also developed a “state of the art” air valve sizing software which is freely available from their website or you can get assistance from Ultra through our contacts page.

If you would like to know more about air valves or want to know what kind of air valve would best suit your system, get in touch through our contact page.